Formats of apriori files for VTD.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

I.  Preliminaries
#################

1.1) Date format:

     Internally dates are kept in VTD in a pair of variables:
     MJD of INTEGER*4 type and TAI of REAL*8 type. TAI keeps
     time alapsed from the midnight. External dates can be
     presetned in two fromats: Solve format compatible with
     ISO 8601 and VEX format.

1.1.1) Solve format presents the date in the form
  
       YYYY.MM.DDThh:mm:ss.ssssssssss
       where YYYY stands for year
               MM stands for the month number
               DD stands for the day of month
               hh stands for the hour
               mm stands for the minute
               ss stands for the second. Decimal point
                  and the fractional part are optional

       Example: 2010.06.20T10:45:51.120391
       This format is compatible with ISO 8601.

       VTD also accepts date with chanracter "_" instead of "T"
       in the 11-th position for better readability.
       Example: 2010.06.20_10:46:36
       This format is incompatible with ISO 8601.

1.1.2) VEX format presnts the date in the form

       YYYYyDDDdHHhNNmSS.SSSSSSs

       where YYYY stands for year
              DDD stands for the day of year
               HH stands for the hour
               NN stands for the minute
               SS stands for the second. Decimal point
                  and the fractional part are optional

       Examples:

       2010y171d10h49m19.129803s
       2010y171d10h50m49s

1.2) Angles

     Angles are presented in the form
     DDD_MM_SS.SSSSS or HH_MM_SS.SSSSS
     where DDD is degree
            MM is arcminue
            SS is arcsecond. Decimal point
               and the fractional part are optional

     or    HH  is hour
           MM  is minute
           SS  is second of time. Decimal point
               and the fractional part are optional

     Delimeters "_" or ":" are acceptable

     Examples: 

     -64_21_58.19083
     +64:21:58
      10:52:02.282921
      10_54_57

II.  Data formats
#################

 1) LEAP_SECOND:
 ===============
    Label:   # LEAP_SECOND file  Version of 2004.01.29
    Purpose: Data file im LEAP_SECOND format contains the dates of
             of the difference TAI-UTC as a function of UTC time tag.
             TAI stands for international atmoic time 
             (Temps Atomique International), and UTC is a non-differential
             step-wise function of time.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/leapsec.dat

    Comment  character: #
    Data record format:

    Field   1:6   A6    Delimiter: Date: 
    Field   7:27  A21   Date as UTC time tag in Solve format.  
    Field  28:38  A11   Delimtere:   TAI-UTC: 
    Field  39:43  F5.1  The difference TAI minus UTC


 2) DE_EPHEMERIDES: 
 ==================
    Label:   ?
    Purpose: Table of Chebyshev coefficients for expansion of positions
             of the Sun, Moon and 9 major planets.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/DE403_JPL.dat

    Comment  character:  n/a
    Data record format:  I completely forgot, sorry. It is rather complicated

 3) STATION_DESCRIPTION:
 =======================
    Label:   # STATION DESCRIPTION   Format version of 2004.01.26
    Purpose: Defines name of the tectinoic plate, type of the 
             mounting, and the value of axis offset for stations.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/station.desc
    
    Comment  character:  #
    Data record format:

    Field   1:8   A8    IVS Site name
    Field  12:15  A4    Antenna mounting code: AZEL, EQUA, X-YN, X-YE, RICH
    Field  18:25  F8.5  Antenna offset (m)
    Field  28:31  A4    Tectonic plate according to NUVEL 
    Field  35:80  A46   Comments

 4) SOURCE_COORDINATES:
 ======================
    Three formats are supported

 4.1) SOU-MODFILE

    Label:   $$  SOU-MODFILE Format pre-2000
    Purpose: Defines IVS source name, source right ascension,
             source declination, and the semi-major axis of the
             error ellipse.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/glo.src

    Comment  character:  $
    Data record format:

    2357-326  00 00 20.399945     -32 21 01.23327     0.60  ! J0000-3221
 
    Field   1:4   A4    Delimeter. Must be blank     
    Field   5:12  A8    IVS name of the source. For 98% sources IVS name 
                        coincides with B1950 name. For remaining sources 
                        a common name is used.

    Field  15:16  I2    Hours of right ascension
    Field  18:19  I2    Minutes of right ascension
    Field  21:28  F9.6  Seconds of right ascension
    Field  35:37  I3    Degrees of declination
    Field  39:40  I3    Minutes of declination
    Field  42:49  F8.5  Arcseconds of declination
    Field  53:58  F6.2  Semi-major axis of the error ellipse. 
                        Units: milli-arcseconds.
                        Value 999.99 indicates that no estimate of the error
                        ellipse is availble. NB: in that case there may be no 
                        compact source at that position.
    Field  61:128 A58   Comments

 4.2) CAT-FORMAT

    Label:   $$  SOU-MODFILE Format pre-2000
    Purpose: Defines IVS source name, IAU J2000 name, source right ascension,
             source declination, information about errors, and correlated
             flux densities.
    Type:    Ascii
    Example: http://astrogeo.org/rfc

    Comment  character:  #
    Data record format:

    Field    1:1    A1    Category: C (calibrator), N (non-calibrator), U (unreliable coordinates)
    Field    4:11   A8    IVS name (B1950)
    Field   13:22   A10   IAU name (J2000.0)
    Field   25:26   I2    Right ascension: hours 
    Field   28:29   I2    Right ascension: minutes
    Field   31:39   F9.6  Right ascension: seconds
    Field   41:43   I3    Declination: degrees
    Field   45:46   I3    Declination: minutes
    Field   48:57   F8.5  Declination: seconds
    Field   58:63   F6.2  Inflated error in right ascension in mas
    Field   65:70   F6.2  Inflated error in declination in mas
    Field   73:78   F6.3  Correlation between right ascension and declination
    Field   80:85   I6    Number of observations used
    Field   88:88   A1    Blank or < or - for X-band total flux density integrated over entire map
    Field   89:92   F4.2  X-band total flux density integrated over entire map,  Jy
    Field   94:94   A1    Blank or < or - for X-band unresolved flux density at VLBA baselines, Jy
    Field   95:98   F4.2  X-band unresolved flux density at long VLBA baselines, Jy
    Field  101:101  A1    Blank or < or - for S-band total flux density integrated over entire map
    Field  102:105  F4.2  S-band total flux density integrated over entire map,  Jy
    Field  107:107  A1    Blank or < or - for S-band unresolved flux density at VLBA baselines
    Field  108:111  F4.2  S-band unresolved flux density at long VLBA baselines, Jy
    Field  114:116  A3    Used Band: X, S or X/S
    Field  119:130  A12   Catalogue name
    
           Missing value: -1.0 
           minus in columns 88, 94, 101 or 107 means that no data in the following column present
           <     in columns 88, 94, 101 or 107 means that the upper limit of the flux density is presented in the following column.

 4.3) GETPAR SOU-FORMAT

    Label:   # GETPAR_SOU format version 1.0  of 2001.05.25
    Purpose: Contains estimates of right ascension and declination of
             sources, as well as their formal uncertainties and 
             correlations between right ascension and declination 
             of the same source.
    Type:    Ascii
    Example: http://astrogeo.org/rfc

    Comment  character:  #
    Data record format:

            Field  Format  Units  Meaning 
    Field  1:8     A8     --      record type identifier: SOU_GCO:
    Field  11:18   A8     --      IVS source name.
    Field  25:26   I2     hours   right ascension. hours part
    Field  27:27   A1     --      separator "_"
    Field  28:29   I2     min.    right ascension. minutes part
    Field  30:30   A1     --      separator "_"
    Field  31:41   F11.8  sec.    right ascension. seconds part
    Field  46:55   F10.4  mas     formal error of right ascension
    Field  62:64   I3     deg.    declination. degrees part.
    Field  65:65   A1     --      separator "_"
    Field  66:67   I2     arcmin  declination. arcminutes part.
    Field  68:68   A1     --      separator "_"
    Field  69:78   F10.7  arcsec  declination. arcseconds part.
    Field  83:92   F10.4  mas     formal uncertainty of declination
    Field  99:104  F6.4   d/l     correlation between the estimates of 
                                  right ascension and declination.
    Field  116:122 I7     --      the number of observations of this source 
                                  used in solution.
    Field  133:139 I7     --      total number of observations of this source.
    Field  151:155 I5     --      the number of sessions of this source used in
                                  solution.
    Field  166:170 I5     --      total number of sessions with this source.
    Field  182:191 A10 	  --      the date of the first session with this source 
                                  used in solution. format: yyyy.mm.dd 
                                  (as integer numbers).
    Field  203:212 A10 	  --      the date of the last session with this source 
                                  used in solution. format: 
                                  yyyy.mm.dd (as integer numbers).
 
 5) STATION_COORDINATES:
 =======================
    Label:   $$  SIT-MODFILE Format 2001.09.26
    Purpose: Defines position of stations at the specified epoch.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/glo.sit
    
    Comment  character:  #
    Epoch of the station catalogue in date Solve formatis defined 
    in the 3rd row at fields 11:21. 

    Data record format:

    Field   1:4    A4     Delimeter. Must be blank
    Field   5:12   A8     IVS station name
    Field  13:15   A3     Delimeter. Must be blank
    Field  16:27   F12.3  Station X-coordinate in meters
    Field  28:31   A4     Delimeter. Must be blank
    Field  32:43   F12.3  Station Y-coordinate in meters
    Field  45:47   A4     Delimeter. Must be blank
    Field  48:59   F12.3  Station Z-coordinate in meters
    Field  60:128  A49    Comments


 6) STATION_VELOCITIES:
 ======================
    Label:   $$  VEL-MODFILE Format 2001.09.26
    Purpose: Defines secular velocities of stations
    Type:    Ascii
    Example: $(VTD_ROOT)/share/glo.vel
    
    Comment  character:  #
    Data record format:

    Field   1:4    A4     Delimeter. Must be blank
    Field   5:12   A8     IVS station name
    Field  13:20   A8     Delimeter. Must be blank
    Field  21:28   F8.2   Station velocity along X-axis in mm/year
    Field  29:36   A8     Delimeter. Must be blank
    Field  37:44   F8.2   Station velocity along Y-axis in mm/year
    Field  45:52   A8     Delimeter. Must be blank
    Field  53:60   F8.2   Station velocity along Z-axis in mm/year
    Field  62:128  A47    Comments


 7) STATION_ECCENTRICITIES:
 ==========================
    Label:   # ECC-FORMAT V 1.0   ECCENTRICITY FILE
    Purpose: Defines a monument number for each VLBI station and an
             eccentricity vector from the monument to the antenna's 
             reference point (axis intersection)
    Type:    Ascii
    Example: $(VTD_ROOT)/share/ECCDAT.ecc
    
    Comment  character:  #
    Data record format:

    Field   3:10  IVS station name
    Field  12:15  Monument number
    Field  18:33  Starting date of validity of the eccentricity vector
    Field  18:21  Year  of starting date of validity
    Field  23:24  Month of starting date of validity
    Field  26:27  Day of month of starting date of validity
    Field  29:30  Hour (UTC) of starting date of validity
    Field  32:33  Minute (UTC) of starting date of validity
    Field  36:51  Ending date of validity of validity of the eccentricity vector
    Field  36:39  Year  of ending date of validity
    Field  41:42  Month of ending date of validity
    Field  44:45  Day of month of ending date of validity
    Field  47:48  Hour (UTC) of ending date of validity
    Field  50:51  Minute (UTC) of ending date of validity
    Field  54:63  First coordinate of eccentricity (in meters)   	 
    Field  65:74  Second coordinate of eccentricity (in meters)   	 
    Field  76:85  Third coordinate of eccentricity (in meters)   	 
    Field  88:90  Type of eccentricity data. Set meaning of eccentricity 
                  coordinates.
                  Two types are supported:
                  NEU  -- 1-st coordinate is a north projection;
                          2-nd coordinate is an east projection;
                          3-rd coordinate is a vertical projection directed up
                         (more precisely speaking it is directed along
                          a normal to the ellipsoid)
                  XYZ  -- 1-st coordinate is a X-coordinate in crust 
                               fixed system;
                          2-nd coordinate is a Y-coordinate in crust 
                               fixed system;
                          3-rd coordinate is a Z-coordinate in crust 
                               fixed system.

 8) AEM_FILE:
 ============

 9) ERM_FILE:
 ============

10) HARMONIC_EOP_FILE:
======================
    Lable:   HEO  Format version of 2007.08.23
    Purpose: Describes small harmonic variations in the Earth
             orientation. "Small" means that the squares of the 
             rotation angles can be neglected.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/heo_20091201.heo

       A file in HEO format consists of records of variable length in
    ASCII coding. The records are separated by a character with decimal
    code 13. The records of the following types are supported:
   
    1) Header record;
    2) N-record: Model name record;
    3) E-record: Time epoch record;
    4) H-record: Harmonic definition records;
    5) A-record: Amplitude definition records;
    6) V-record: Velocities definition records;
    7) S-record: Amplitude errors definition records;
    8) R-record: Velocities errors definition records;
    9) Trailer record.
   
       Records which start from # character are considered as comments.
   
       The first record of a valid file in HEO format is the header record.
    It is followed by the model name record, time epoch record and then by one
    or more harmonic definition records and one or more harmonic definition
    records. The last record is a trailer record. All harmonic definition records
    should precede amplitude and velocity definition records. Names of a harmonic
    in the amplitude or velocity records should be defined in the harmonic
    definition record. The number of velocity records can be less than the number
    of amplitude records, and the number of amplitude records can be less than
    the number of harmonic records. If a harmonic is not defined in an amplitude
    records, its amplitude is considered to be zero. If a harmonic is not defined
    in a velocity records, the rate of change of the amplitude of that harmonic
    is considered to be zero.
   
       Records format:
   
    1) A header record contains the string
       "HEO  Format version of 2007.08.23 "
   
       The header record allows to distinguish the valid file in the
       HEO format from files in other formats and tells to a parsing software
       that is the version of the format.
   
   
    2) A name record defines the name of the model of the harmonic Earth
       orientation variations.
   
    Format of an N-record:
    ----------------------
   
    Field  1:1   A1     -- Records ID: letter N (decimal code 78).
    field  2:3   a2     -- delimiters: blanks.
    Field  4:80  A77    -- 77-letter long model name. May contain any
                           characters in the decimal range [32, 255].
   
    3) An epoch record defines the epoch of the expansion.
       An expansion may have mixed terms (t-t0)*sin(at+p), (t-t0)*cos(at+p),
       where t is time. The E-record defines the epoch t0 in mixed terms.
       If an expansion does not have mixed terms, then the epoch defined in
       this record is not used. Time scale TDT is used for defining the
       reference epoch.
   
    Format of a E-record:
    ---------------------
   
    Field  1:1   A1     -- Records ID: letter E (decimal code 69).
    field  2:2   a2     -- delimiters: blanks.
    Field  4:7   I4     -- Year
    field  8:8   a1     -- delimiter: letter . (decimal code 46).
    Field  9:10  I2     -- The index of the month in the year in the range [1,12]
    field 11:11  a1     -- delimiter: letter . (decimal code 46).
    Field 12:13  I2     -- The index of the day in the month in the range [1,31]
    field 14:14  a1     -- delimiter: letter - (decimal code 45).
    Field 15:16  I2     -- Hour in the range [0,23]
    field 17:17  a1     -- delimiter: letter : (decimal code 58).
    Field 18:19  I2     -- Minute in the range [0,23]
    field 20:20  a1     -- delimiter: letter : (decimal code 58).
    Field 21:24  F4.1   -- Seconds in the range [0.0, 59.9]
   
   
    4) A harmonic definition record defines the argument of the harmonic in
       the form {phase + freq*(t-tr) + 1/2*accel*(t-tr)**2}  where t is
       time in TDT time scale and tr is the reference epoch J2000.0,
       01 January 2000, 12 hours TDT. The file cannot contain more than one
       definition of the same harmonic.
   
   
    Format of an H-record:
    ----------------------
   
    Field  1:1   A1     -- Records ID: letter H (decimal code 72).
    field  2:3   a2     -- delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. May contain any
                           characters with decimal codes 32-255, but blanks
                           are allowed only at the end of the harmonic name.
                           This field should not necessarily have a special
                           meaning. Parsing software should not try to
                           interpret this name.
    field 12:13  a2     -- delimiters: blanks.
    Field 14:25  F11.9  -- Phase of the harmonic in float format.
                           Units: rad.
    field 26:27  a2     -- delimiters: blanks.
    Field 28:46  D19.12 -- Frequency of the harmonic in float format.
                           Units: rad/sec.
    field 47:48  a2     -- delimiters: blanks.
    Field 49:59  D11.4  -- Acceleration of the harmonic in float format.
                           Units: rad/sec**2.
    field 60:60  a1     -- delimiters: blanks.
    field 61:80  A20    -- Comment. Parser ignores contents of this field.
   
   
    5) An amplitude record specifies the harmonic and 4 amplitudes of
       the variation of the Earth orientation: the in_phase polar motion
       (PM_amp_cos), the out_of_phase polar motion (PM_amp_sin), the in_phase
       rotation around E3 axis (E3_amp_cos), adn the out_of_phase rotation
       around E3 axis (E3_amp_sin). A file cannot contain more than one amplitude
       record for the same harmonic. The harmonic referred in an amplitude record
       must be defined in the preceding harmonic definition record.
   
       These amplitudes allows to define instantaneous small Euler angles of
       the perturbations in the Earth rotation with respect to an apriori model
       in this way:
   
       E1 = [ PM_amp_cos + PM_vel_cos*(t-t0) ] *
            cos { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
          + [ PM_amp_sin + PM_vel_sin*(t-t0) ] *
            sin { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
   
       E2 = [ PM_amp_cos + PM_vel_cos*(t-t0) ] *
            sin { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
          - [ PM_amp_sin + PM_vel_sin*(t-t0) ] *
            cos { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
   
       E3 = [ E3_amp_cos + E3_vel_cos*(t-t0) ] *
            cos { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
          + [ E3_amp_sin + E3_vel_sin*(t-t0) ] *
            sin { (ut1-tdt)*2*pi/86400 + phase + freq*(t-tr) + 1/2*accel*(t-tr)**2 }
   
       Where
   
       E1 -- rotation around axis 1 (+Y angle of the polar motion)
       E2 -- rotation around axis 2 (+X angle of the polar motion)
       E3 -- rotation around axis 3 (-1.0027*Ut1 angle of the Earth's rotation)
   
       t-tr  -- The interval of time in scale TAU elapsed since
                01 January 2000, 12 hours TAI, in seconds
       t-t0  -- The interval of time in scale TAI elapsed since the reference
                epoch for the expansion defined in the E-record, in seconds.
   
   
    Format of a A-record
    ---------------------
   
    Field  1:1   A1     -- Record ID: letter A (decimal code 65).
    field  2:3   a2     -- Delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. The harmonic name
                           must be defined in a preceding H-record.
    field 12:13  a2     -- Delimiters: blanks.
    Field 14:25  F12.0  -- PM_amp_cos -- cosine amplitude of the small angle
                           of polar motion. Units: prad.
    field 26:26  a1     -- delimiter: blank.
    Field 27:38  F12.0  -- PM_amp_sin -- sine amplitude of the small angle
                           of polar motion. Units: prad.
    field 39:39  a2     -- Delimiters: blanks.
    Field 41:52  F12.0  -- E3_amp_cos -- cosine amplitude of the small angle
                           of the Earth rotation around axis 3. Units: prad.
    field 53:53  a1     -- Delimiter: blank.
    Field 54:65  F12.0  -- E3_amp_sin -- sine amplitude of the small angle
                           of the Earth rotation around axis 3. Units: prad.
   
   
    6) A velocity record specifies rates of changes of the amplitudes of
       the harmonic of the variation of the Earth orientation: in phase polar
       motion (PM_vel_cos), out_of_phase polar motion (PM_vel_sin), in_phase
       rotation around E3 axis (E3_vel_cos), out_of_phase rotation around
       E3 axis (E3_vel_sin). A file cannot contain more than one velocity
       record for the same harmonic. The harmonic referred in an velocity record
       must be defined in the preceding harmonic definition record.
   
   
    Format of a V-record
    ---------------------
   
    Field  1:1   A1     -- Record ID: letter A (decimal code 65).
    field  2:3   a2     -- Delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. The harmonic name
                           must be defined in a preceding H-record.
    field 12:13  a2     -- Delimiters: blanks.
    Field 14:25  F12.0  -- PM_vel_cos -- rate of change of the cosine amplitude
                           of the small angle of polar motion.
                           Units: 10^{-21} rad/sec.
    field 26:26  a1     -- delimiter: blank.
    Field 27:38  F12.0  -- PM_amp_sin -- rate of change of the sine amplitude
                           of the small angle of polar motion.
                           Units: 10^{-21} rad/sec.
    field 39:40  a2     -- Delimiters: blanks.
    Field 41:52  F12.0  -- E3_amp_cos -- rate of change of the cosine amplitude
                           of the small angle of the Earth rotation around axis 3.
                           Units: 10^{-21} rad/sec.
    field 53:53  a1     -- Delimiter: blank.
    Field 54:65  F12.0  -- E3_amp_sin -- rate of change of the sine amplitude
                           of the small angle of the Earth rotation around
                           axis 3. Units: 10^{-21} rad/sec.
   
    7) An amplitude error record specifies the harmonic and 4 formal uncertainties
       of amplitudes of the variation of the Earth orientation: the error of the
       in_phase polar motion (PM_amp_cos_err), the error of the out_of_phase
       polar motion (PM_amp_sin_err), the error of the in_phase rotation around
       E3 axis (E3_amp_cos_err), and the error of the out_of_phase rotation around
       E3 axis (E3_amp_sin). A file cannot contain more than one amplitude error
       record for the same harmonic. If information about errors of the amplitude
       of the harmonic is unavilalbe, the record can be omitted. The harmonic
       referred in an amplitude error record must be defined in the preceding
       harmonic definition record.
   
   
    Format of a S-record
    ---------------------
   
    Field  1:1   A1     -- Record ID: letter A (decimal code 83).
    field  2:3   a2     -- Delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. The harmonic name
                           must be defined in a preceding H-record.
    field 12:13  a2     -- Delimiters: blanks.
    Field 15:26  F12.1  -- PM_amp_cos_err -- cosine amplitude of the small
                           angle of polar motion. Units: prad.
    field 27:27  a1     -- delimiter: blank.
    Field 28:39  F12.1  -- PM_amp_sin_err -- sine amplitude of the small
                           polar motion. Units: prad.
    field 40:41  a2     -- Delimiters: blanks.
    Field 42:53  F12.1  -- E3_amp_cos_err -- cosine amplitude of the small
                           angleof the Earth rotation around axis 3. Units: prad.
    field 54:54  a1     -- Delimiter: blank.
    Field 55:66  F12.1  -- E3_amp_sin_err -- sine amplitude of the small angle
                           of the Earth rotation around axis 3. Units: prad.
   
   
    8) A velocity error record specifies errors of rates of changes of the
       amplitudes of the harmonic of the variation of the Earth orientation:
       the in_phase polar motion (PM_vel_cos_err), the out_of_phase polar motion
       (PM_vel_sin_err), the in_phase rotation around E3 axis (E3_vel_cos_err),
       and the out_of_phase rotation around E3 axis (E3_vel_sin_err).
       A file cannot contain more than one velocity record for the same harmonic.
       If information about errors of the rate of change of amplitude of the
       harmonic is unavilalbe, the record can be omitted. The harmonic referred
       in an velocity record must be defined in the preceding harmonic
       definition record.
   
   
    Format of a R-record
    ---------------------
   
    Field  1:1   A1     -- Record ID: letter R (decimal code 82).
    field  2:3   a2     -- Delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. The harmonic name
                           must be defined in a preceding H-record.
    field 12:13  a2     -- Delimiters: blanks.
    Field 14:25  F12.0  -- PM_vel_cos_err -- error of the rate of change of
                           the cosine amplitude of the small angle of polar
                           motion. Units: 10^{-21} rad/sec.
    field 26:26  a1     -- delimiter: blank.
    Field 27:38  F12.0  -- PM_amp_sin_err -- error of the rate of change of
                           the sine amplitude of the small angle of polar motion.
                           Units: 10^{-21} rad/sec.
    field 39:40  a2     -- Delimiters: blanks.
    Field 41:52  F12.0  -- E3_amp_cos_err -- error of rate of change of
                           the cosine amplitude of the small angle of the Earth
                           rotation around axis 3.
                           Units: 10^{-21} rad/sec.
    field 53:53  a1     -- Delimiter: blank.
    Field 54:65  F12.0  -- E3_amp_sin_err -- error of rate of change of the sine
                           amplitude of the small angle of the Earth rotation
                           around axis 3. Units: 10^{-21} rad/sec.
   
   
    9) Trailer record is the same as the header record.

11) EOP_SERIES:
===============
    Label:   EOP-MOD Ver 2.0  
    Purpose: Define the time series of the Earth orientation parameters,
             such as pole coordinates and UT1-TAI angle.
    Type:    Ascii, records of fixed length
    Example: $(VTD_ROOT)/share/vlbi_apr.erp
    NB:      1) All records of this file must have lenght 76 bytes
             2) non-standrd units are used

    Comment  character:  #
    Header record format:

    Filed  1:15      Label: EOP-MOD Ver 2.0  
    Field 18:26 F9.1 Julain date (TAI) of the first data record     
    Field 28:33 F6.2 Time step in days
    Field 34:39 I6   The number of records
    Field 42:48 A7   Meaning of the 4th column 
    Field 52:56 A5   Meaning is lost
    Field 57:76 A18  Delimeter: blank

    Data record format:

    Filed  1:9  F9.1 Julian date (TAI)
    Filed 11:17 F7.4 X pole coordinate. Units: 0.1 arcsec
    Filed 19:25 F7.4 Y pole coordinate. Units: 0.1 arcsec
    Filed 27:35 I9   UT1-TAI. Units: micrisecond of time
    Filed 36:76 A41  some information not used by VTD. 
                     Its meaning is forgotten



12) POSVAR_MOD:  (HARMONIC_MODEL)
=================================
    Label:   HARPOS  Format version of 2002.12.12
    Purpose: Describes site displacements which can
             be represented by a finite set of harmonic components.
    Type:    Ascii
    Example: $(VTD_ROOT)/share/2007b_oclo.hps

      A file in HARPOS format consists of records of variable length in
    ASCII coding. The records are separated by a character with decimal
    code 13. The records of the following types are supported:
     
    1) Header record;
    2) Harmonic definition records;
    3) Site definition records;
    4) Displacement definition records;
    5) Trailer record.
     
       Records which start from # character are considered as comments.
     
       Each valid file in HARPOS format has the first header record, one
    or more harmonic definition records, one or more site definition
    records and one or more displacement definition records. The last
    record is a trailer record. All harmonic definition records should
    precede site definition records. All site definition records should
    precede displacement definition records.
     
       Records format:
     
    1) A header record contains the string
       "HARPOS Format version of 2002.12.12"
     
       The header record allows to distinguish the valid file in the
       HARPOS format from files in other formats.
     
    2) A harmonic definition record defines the argument of the harmonic in
       the form {phase + freq*(t-t0) + 1/2*accel*(t-t0)**2}  where t is
       time in TDT time scale and t0 is the reference epoch J2000.0,
       01 January 2000, 12 hours TDT. The file cannot contain more than one
       definition of the same harmonic.
     
    Format of an H-record:
    ----------------------
     
    Field  1:1   A1     -- Records ID: letter H (decimal code 72).
    field  2:3   a2     -- delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. May contain any
                           characters with decimal codes 32-255, but blanks
                           are allowed only at the end of the harmonic name.
                           This field should not necessarily have a special
                           meaning. Parsing software should not try to
                           interpret this name.
    field 12:13  a2     -- delimiters: blanks.
    Field 14:26  D13.6  -- Phase of the harmonic in float format.
                           Units: rad.
    field 27:28  a2     -- delimiters: blanks.
    Field 29:47  D19.12 -- Frequency of the harmonic in float format.
                           Units: rad/sec.
    field 48:49  a2     -- delimiters: blanks.
    Field 50:59  D10.3  -- Acceleration of the harmonic in float format.
                           Units: rad/sec**2.
    field 60:80  a21    -- delimiters: blanks.
     
    3) A site definition record defines the site identifier and site
       coordinates in a crust-fixed reference frame. The file cannot
       contain more than one definition of the same site.
     
    Format of an S-record:
    ----------------------
     
    Field  1:1   A1     -- Record ID. Should be letter S (decimal code 83)
    Field  2:3   A2     -- Delimiters: blanks.
    Field  4:11  A8     -- 8-letter long site identifier. May contain
                           any characters with decimal codes 32-255, but
                           blanks are allowed only at the end of the site
                           identifier. This site identifier should be
                           unique among S-records. This field should not
                           necessarily have a special meaning. Parsing
                           software should not try to interpret it.
    field 12:13  a2     -- delimiters: blanks.
    Field 14:26  F13.4  -- Site X coordinate in a crust fixed reference
                           frame. Units: meters.
    field 27:27  a1     -- delimiters: blanks.
    Field 28:40  F13.4  -- Site Y coordinate in a crust fixed reference
                           frame. Units: meters.
    field 41:41  a1     -- delimiters: blanks.
    Field 42:54  F13.4  -- Site Z coordinate in a crust fixed reference
                           frame. Units: meters.
    field 55:56  a2     -- delimiters: blanks.
    Field 57:64  F8.4   -- Site geocentric latitude, positive to north,
                           in degrees. This field is for information only.
                           Parsing software MUST ignore it.
    field 65:65  a1     -- delimiters: blanks.
    Field 66:73  F8.4   -- Site longitude, positive towards east,
                           in degrees. This field is for information only.
                           Parsing software MUST ignore it.
    field 74:74  a1     -- delimiters: blanks.
    Field 75:80  F6.1   -- Site height above the reference ellipsoid
                           in meters. This field is for information only.
                           Parsing software MUST ignore it.
     
    4) A data record specifies the site, the harmonic and 6 amplitudes of
       displacements: Up cosine, East cosine, North cosine, Up sine,
       East sine, North sine. A file cannot contain more than one data
       record for the same harmonic, the same site. The site and the
       harmonic referred in a data record must be defined in the preceding
       site and harmonic definition records.
     
       Notation "Up cosine" and "Up sine" amplitudes of the displacement
       means that the radial component of the topocentric vector of the
       displacement, which is parallel to the vector from the geocenter to
       the site, depends on time in the following way:
     
       D_up= Ampl_cos_up * cos {phase + freq*(t-t0) + 1/2*accel*(t-t0)**2} +
             Ampl_sin_up * sin {phase + freq*(t-t0) + 1/2*accel*(t-t0)**2}
     
       Analogously, "East cosine", "East sine" amplitudes define time
       dependence of the east component of the displacement vector, and
       "North cosine", "North sine" define time dependence of the north
       component.
     
    Format of a D-record:
    ---------------------
     
    Field  1:1   A1     -- Record ID: letter D (decimal code 68).
    field  2:3   a2     -- delimiters: blanks.
    Field  4:11  A8     -- 8-letter long harmonic name. The harmonic name
                           must be defined in a preceding H-record.
    field 12:13  a2     -- delimiters: blanks.
    Field 14:21  A8     -- 8-letter long site identifier. The site
                           identifier must be defined in a preceding
                           S-record.
    field 22:24  a3     -- delimiters: blanks.
    Field 25:32  F8.5   -- Cosine amplitude of the Up component of the
                           displacement vector. Up direction is along the
                           vector from the geocenter to the site.
                           Units: meters.
    field 33:33  A1     -- delimiter: blank.
    Field 34:41  F8.5   -- Cosine amplitude of the East component of the
                           displacement vector. Units: meters.
    field 42:42  a1     -- delimiter: blank.
    Field 43:50  F8.5   -- Cosine amplitude of the North component of the
                           displacement vector. Units: meters.
    field 51:53  a3     -- delimiter: blanks.
    Field 54:61  F8.5   -- Sine amplitude of the Up component of the
                           displacement vector. Up direction is along the
                           vector from the geocenter to the site.
                           Units: meters.
    field 62:62  a1     -- delimiter: blank.
    Field 63:70  F8.5   -- Sine amplitude of the East component of the
                           displacement vector. Units: meters.
    field 71:71  a1     -- delimiter: blank.
    Field 72:79  F8.5   -- Sine amplitude of the North component of the
                           displacement vector. Units: meters.
    field 80:80  a1     -- delimiter: blank.
     
     
    5) Trailer record is the same as the header record.
   

13) POSVAR_MOD:  (TIME_SERIES):
===============================
    Label:   BINDISP
    Purpose: describing time series of site position 
             variations. A file in this format contains three 
             components of the 
             displacement vector of a specific site equally sampled 
             within a certain time range.
    Type:    Binary, little endian
    Example: http://astrogeo.org/scr/aplo_bds


       A file consists of records of fixed length. Record length is 
    8 bytes. A file has 8 header records and at least one data record 
    which follows header records.

    Header record 1:
    ----------------
    
    Field  1:8  A8   -- Magic record. Should be "BINDISP " for  
                        a valid file.
    
    Header record 2:
    ----------------
    
    Field 1:4   I*4  -- Integer modified Julian of the format 
                        revision date.
    Field 5:5   A1   -- Identifier for used binary integer format.
                        Supported identifiers:
                        B -- big endian format
                        L -- little endian format
    Field 6:6   A1   -- Identifier for used binary float format.
                        Supported identifiers:
                        I -- IEEE 754/854 format.
                        D -- Dec format.
    Field 7:8   I*2  -- Reserved. filled with binary value 0.
    
    Header record 3:
    ----------------
    
    Field 1:8   A8   -- 8-letter long site identifier. May contain 
                        any characters with decimal codes 32-255, but 
                        blanks are allowed only at the end of the site 
                        identifier. This field should not necessarily 
                        have a special meaning. Parsing software should
                        not try to interpret it.
    
    Header record 4:
    ----------------
    
    Field 1:4   I*4  -- The total number of data records.
    Field 5:8   R*4  -- Sampling interval in seconds: the interval
                        between two consecutive epochs.
    
    Header record 5:
    ----------------
    
    Field 1:8   R*8  -- X site coordinate in a crust fixed reference 
                        frame. Units: meter.
    
    Header record 6:
    ----------------
    
    Field 1:8   R*8  -- Y site coordinate in a crust fixed reference 
                        frame. Units: meter.
    
    Header record 7:
    ----------------
    
    Field 1:8   R*8  -- Z site coordinate in a crust fixed reference 
                        frame. Units: meter.
    
    Header record 8:
    ----------------
    
    Field 1:4   I*4  -- Integer modified Julian data at the midnight
                        of the time epoch of the first data record.
    Field 5:8   R*4  -- Time in TDT elapsed from the midnight od
                        the time epoch of the first data record,
                        in seconds.
    
    Data record:
    ------------
    
    Field 1:2   I*2  -- X coordinate of site displacement for a given 
                        epoch in a crust-fixed reference system. 
                        Units: 1.D-5 meter.
    
    Field 3:4   I*2  -- Y coordinate of site displacement for a given 
                        epoch in a crust-fixed reference system. 
                        Units: 1.D-5 meter.
    
    Field 5:6   I*2  -- Z coordinate of site displacement for a given 
                        epoch in a crust-fixed reference system. 
                        Units: 1.D-5 meter.
    
    Field 7:8   I*2  -- Reserved. Filled with binary value 0.
    
      Comments:
    
      1. Data records follow in chronological order. No records can be 
         missed. The epoch of the J+1 th record is the epoch of the 
         J -th record plus the sampling interval. The epoch of the K-th 
         physical record of the file is (MJD,TDT) + (K-9)*Sample_interval. 
         Physical records are counted from 1.
    
      2. Maximal displacements in site positions which can be described  
         in this file cannot exceed by modulo 327mm.
    

13) POSVAR_MOD:  (B_S_LINE):
============================
    Label:   BSPPOS Format version of 2007.10.30"
    Purpose: To describe site displacements which can
             be represented as the sum of the polynomial of the first 
             degree and an expansion with the B-spline basis. The expansion 
             is defined on a expanded non-descending sequence of knots. 
             The first and the last knot has multiplicity 1-degree, other 
             knots are represented as simple. The sequence may have several 
             consecutive knots with equal epochs, except the first and 
             the last. The number of knots with the same epochs should 
             not exceed the degree of the B-spline basis. The expanded 
             sequence of knots has indexes 
             1-degree, 1-degree+1, ... 0, 1, 2, ... N, N+1, N+2, ... N+degree,
             i.e. in the expanded sequence the first and the last knot 
             are split into the set of knots with the number of elements 
             equal to the degree.

             BSPPOS file provides the number of knots, the degree of 
             the B-spline basis, apriori site position, time epochs of 
             knots, estimates of B-spline coefficients, global site position, 
             and global site velocity.
 
       A file in BSPPOS format consists of records of variable length in
    ASCII coding. The records are separated by a character with decimal
    code 13. The records of the following types are supported:
     
     1) Header record
     2) Solution identifier
     3) Solution date
     4) Record that specifies the total number of sites
     5) Site definition record
     6) Record that specifies the B-spline degree
     7) Record that specifies the number of knots for spline for this site
     8) Record that specifies the reference epoch for site positions
     9) Record that specifies position at reference epoch 
    10) Record that specifies site velocity 
    11) Record that specifies epoch of the spline 
    12) Record that specifies B-spline coefficients
    13) Record that specifies elements of the covarinace matrix of B-spline 
        coefficients (optional)
    14) Trailer record
     
       The records should be placed in this order. Records 5-10 are repeated 
    for each site, records 11-12 are repeated for each spline knot and each
    site.
    
       Records which start from # character are considered as comments.
     
     
     1. Header record
        A header record contains the string
        "BSPPOS Format version of 2007.10.30"
     
        The header record allows to distinguish the valid file in the
        BSPPOS format from files in other formats.
      
     2. Solution identifier
    
        Field  1:7    A7   Field ID: SOL_ID:
        Field  8:10   a3   Delimiter (blank)
        Field  11:43  A32  Text identifying the solution
       
    
     3. Solution date
    
        Field  1:9    A9   Field ID: SOL_DATE:
        Field  10:10  a1   Delimiter (blank)
        Field  11:29  A19  Date of the solution in ISO format
       
     4. Record that specifies the total number of sites
    
        Field  1:6    A6   Field ID: N_STA:
        Field  7:7    a1   Delimiter (blank)
        Field  8:11   I4   The total number of sites
    
     5. Site definition record
    
        Field  1:2    A2    Field ID: S:
        Field  3:3    a3    Site ID: an arbitrary sequence of letters.
                            NB: parsing software SHOULD NOT ATTEMPT to interpret
        Field  8:11   I4    The total number of sites
        Field 12:13   a2    Delimiter (blanks)
        Field 14:26   F13.5 X-coordinate of the site in the crust fixed coordinate system
        Field 27:27   a1    Delimiter (blank)
        Field 28:40   F13.5 Y-coordinate of the site in the crust fixed coordinate system
        Field 41:41   a1    Delimiter (blank)
        Field 42:54   F13.5 Z-coordinate of the site in the crust fixed coordinate system
        Field 12:13   a2    Delimiter (blanks)
        Field 57:64   F8.4  Site geocentric latitude.
        Field 65:65   a1    Delimiter (blank)
        Field 66:73   F8.4  Site geocentric longitude positive to East in [0,360]
        Field 74:74   a1    Delimiter (blank)
        Field 75:80   F5.1  Site height above the reference ellipsoid
       
    
     6. Record that specifies the B-spline degree
    
        Field  1:6    A6    Field ID: L_DEG:
        Field  7:7    a1    Delimiter (blank)
        Field  8:11   I4    Spline degree
        Field 12:18   a7    Delimiter  STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
    
     7. Record that specifies the number of knots for spline for this site
    
        Field  1:6    A6    Field ID: N_NOD:
        Field  7:7    a1    Delimiter (blank)
        Field  8:11   I4    The number of knots for this site
        Field 12:18   a7    Delimiter  STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
    
     8. Record that specifies the reference epoch for site positions
    
        Field  1:6    A6    Field ID: R_EPC:
        Field  7:18   a12   Delimiter        STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 33:34   a2    Delimiter (blanks)
        Field 35:57   A23   Reference epoch for site positions in TAI in ISO format.
    
     9. Record that specifies position at reference epoch 
    
        Field  1:6    A6    Field ID: P_EST:
        Field  7:18   a12   Delimiter        STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 33:34   a2    Delimiter (blanks)
        Field 35:48   F14.6 X component of site position at the reference epoch in meters
        Field 49:49   a1    Delimiter (blanks)
        Field 50:63   F14.6 Y component of site position at the reference epoch in meters
        Field 64:64   a1    Delimiter (blanks)
        Field 65:78   F14.6 Z component of site position at the reference epoch in meters
    
    10. Record that specifies site velocity 
    
        Field  1:6    A6    Field ID: P_EST:
        Field  7:18   a12   Delimiter        STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 33:34   a2    Delimiter (blanks)
        Field 35:48   F14.6 X component of site velocity in m/s
        Field 49:49   a1    Delimiter (blanks)
        Field 50:63   F14.6 Y component of site velocity in m/s
        Field 64:64   a1    Delimiter (blanks)
        Field 65:78   F14.6 Z component of site velocity in m/s
    
    11. Record that specifies epoch of the spline 
    
        Field  1:6    A6    Field ID: EPOCH:
        Field  7:7    a1    Delimiter (blank)
        Field  8:11   I4    The knot index starting from 1-L_DEG
        Field 12:18   a7    Delimiter  STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 35:57   A23   Epoch of the knot in TAI in ISO fort mat.
    
    12. Record that specifies B-spline coefficients
    
        Field  1:6    A6    Field ID: EPOCH:
        Field  7:7    a1    Delimiter (blank)
        Field  8:11   I4    The knot index starting from 1-L_DEG
        Field 12:18   a7    Delimiter  STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 33:35   a3    Delimiter (blanks)
        Field 36:48   F13.6 B-spline coefficient for X component of position of this site, this knot
        Field 49:49   a1    Delimiter (blanks)
        Field 50:62   F13.6 B-spline coefficient for Y component of position of this site, this knot
        Field 63:63   a1    Delimiter (blanks)
        Field 64:76   F13.6 B-spline coefficient for Z component of position of this site, this knot
    
    13. Record that specifies elements of the covariance matrix of B-spline 
        coefficients (optional). Covariance matrix is a 4-dimensional array
        in the crust-fixed terrestrial coordinate system. The first two 
        dimensions run through the knot indexes + global position + global 
        velocity. The second two dimensions, the 3rd and the 4th, run through
        components of the coordinate vectors: X, Y, Z.
    
        Field  1:6    A6    Field ID: EPOCH:
        Field  7:18   a12   Delimiter (blank)
        Field 12:18   a7    Delimiter  STA: 
        Field 19:22   I4    Site index. The index of the site definition
                            record for this site, counted from 1
        Field 23:24   a2    Delimiter (blanks)
        Field 25:32   A8    Site name specified in the preceding site definition
                            record
        Field 33:41   a9    Delimiters
        Field 43:43   I1    The first component of the displacement vector in the 
                            terrestrial coordinate system. Components runs as 
                            X, Y, and Z.
        Field 49:49   a1    Delimiter (blanks)
        Field 50:52   a3    Delimiters
        Field 53:56   I4    The first covariance element index. Index starts from 
                            1-L_DEG and runs through N_NOD+L_DEG-1. The element 
                            with index N_NOD+L_DEG+1 corresponds to the global 
                            position, the element with index N_NOD+L_DEG corresponds 
                            to the global velocity, other indexes correspond to knot
                            index.
        Field 57:65   a9    Delimiters
        Field 66:66   I1    The second component of the displacement vector in the 
                            terrestrial coordinate system. Components runs as 
                            X, Y, and Z.
        Field 67:75   a9    Delimiters
        Field 76:79   I4    The second covariance element index. Index starts from 
                            1-L_DEG and runs through N_NOD+L_DEG-1. The element 
                            with index N_NOD+L_DEG+1 corresponds to the global 
                            position, the element with index N_NOD+L_DEG corresponds 
                            to the global velocity, other indexes correspond to knot
                            index.
        Field 80:86   a7    Delimiters
        Field 87:99   D13.6 The element of the covariance matrix
    
    
    14. Trailer record
    
        The same as the header record, string:
        "BSPPOS Format version of 2007.10.30"


14) ANTENNA_DEFORMATIONS_FILE: 	
==============================
    Label:   $ Antenna Gravity Deformation File  Format Version of 2008.04.25
    Purpose: Contains the table of the antenna focus line as a function
             of elevation angle.
    Type:    ascii
    Example: $(VTD_ROOT)/share/agd.dat

    Comment  character: #
    Data record format:

     1:5   A3    Delimeter: "AGD  "
     6:13  A8    IVS station name
    14:15  A2    Delimiter: blank
    16:22  A7    Focus type
    23:24  A2    Delimiter: blank
    25:28  F4.1  Elevation (in deg)
    29:30  A2    Delimiter: blank
    31:37  F7.3  Focus length change (in mm)

15) SLANTED_PATH_DELAY_BIAS_FILE:   
=================================
    Label:   SPD_3D_BIAS   Format version of 2010.05.18
    Purpose: Detine empirical bias and scale facord for the 
             slanted path delay model. Teh non-hydrostatic
             component of the Slanted path delay is to 
             be multiplied by the scale and added the bias.
    Example: n/a
    Comment  character: #
    Data record format:


       A file in the SPD_ASCII format consists of records of variable
    length in ASCII coding. The records are separated by a character with
    decimal code 13. The records are grouped into sections. Sections follow
    in this order:
    
     1) N-record -- defines the number of records in further other
                    sections.
    
     2) S-record -- defines name and coordinates of stations for which path
                    delay have been computed.
    
     3) B-record -- defines bias and scaling factor
    
    
    Format of an N-record:
    ----------------------
    
    Field  1:1   A1    -- Record ID: letter "N".
    field  2:3   a2       delimiter: blank.
    Field  4:7   I4    -- Number of M-records in the file. i.e. brief algorithm
                          description and options used during computations.
    field  8:9   a2       delimiter: blank.
    field 10:13  I4    -- Number of I-records in the file, i.e. the number of
                          lines with a brief description of the numeric
                          model of the atmosphere used during computation.
    field 14:15  a2       delimiter: blank.
    field 16:21  I6    -- Number of S-records in the file, i.e. the number
                          of stations.
    field 22:23  a2       delimiter: blank.
    field 24:27  I4    -- Number of E-records in the file, i.e. the number
                          elevations in the grid.
    field 28:29  a2       delimiter: blank.
    field 30:33  I4    -- Number of A-records in the file, i.e. the number
                          azimuths in the grid.
    
    
    Format of an S-record:
    ----------------------
    
    Field  1:1   A1    -- Record ID: letter "S".
    field  2:3   a2       delimiter: blanks.
    field  4:9   I6    -- station index
    field 10:11  a2       delimiter: blanks.
    Field 12:19  A8    -- 8-letter long site identifier. May contain
                          any characters with decimal codes 32-255, but
                          blanks are allowed only at the end of the site
                          identifier. This site identifier should be unique
                          among S-records. This field should not
                          necessarily have a special meaning. Parsing
                          software SHOULD NOT TRY TO INTERPRET it.
    field 20:21  a2       delimiter: blanks.
    Field 22:33  F12.3 -- X site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 34:34  a1       delimiter: blank.
    Field 35:46  F13.4 -- Y site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 47:47  a1       delimiter: blank.
    Field 48:59  F13.4 -- Z site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 60:61  a2       delimiter: blanks.
    Field 62:69  F8.4  -- Site geocentric latitude, positive to north,
                          in degrees. This field is for information only.
                          Parsing software MUST ignore it.
    field 70:70  a1       delimiter: blank.
    Field 71:78  F8.4  -- Site longitude, positive towards east,
                          in degrees. This field is for information only.
                          Parsing software MUST ignore it.
    field 79:80  a2       delimiter: blank.
    Field 81:86  F6.1  -- Site height above the reference ellipsoid in
                          meters. This field is for information only.
                          Parsing software MUST ignore it.
    field 87:87  a1       delimiter: blank.
    Field 88:93  F6.1  -- Site height above the geoid in meters. This field
                          is for information only.
                          Parsing software MUST ignore it.
    
    Format of an B-record:
    ----------------------
    
    Field  1:1   A1    -- Record ID: letter "B".
    field  2:11  a10   -- delimeter: blank
    Field 12:19  A8    -- 8-letter long site identifier. 
    field 20:24  a5    -- delimeter: blank
    Field 25:34  D10.3 -- Slanted path delay offset. Units: seconds
    field 35:37  a3    -- delimeter: blank
    Field 38:44  F7.4  -- Slatned path delay scale factor



16) EXTERNAL_DELAY_DIR: 		
=======================
    Label:   spd_3d_bin  1.0 version of 2009.01.07 LE
    Purpose: Contains results of computing slanted path delay of 
             radiowave propagation through the 3D, continuous,
             heterogeneous atmosphere. The path delay is defined as 
             a difference in the propagation time between the emitter 
             and the receiver through the atmosphere and the propagation 
             between these two points along the geodetic line in 
             vacuum. The path delay is computed for a set of stations for
             a certain epoch at a regular grid of azimuths and elevations.
             The grid is equidistant at azimuths and non-equidistant at 
             elevation angles. The values of path delays computed on 
             a grid can be used for computing coefficients of the 
             interpolating functions that enable us to compute
             the path delay in an arbitrary direction.
    Example: http://astrogeo.org/spd_data/spd_6h_bin
    Type:    Binary, little endian.

    File in spd_3d_bin format consists of rescords of 7 types.
    The type of each reacord is determined by the first 
    8-characters ling field prefix. The records follow in this order:

    LAB_REC -- Defines offsets, sizes and the number of other records
    TIM_REC -- Defines the start time, stop time of DEL records 
               and the time step 
    STA_REC -- Defines station coordinates
    MOD_REC -- Defines the slanted path model type and the model description
    MET_REC -- Defines escription of the numerical weather model used 
               for computation
    ELV_REC -- Defines the elevation axis for the 2D grid of
               path delays through the neutral atmosphere
    AZM_REC -- Defines the azimuth axis for the 2D grid of
               path delays through the neutral atmosphere
    DEL_REC -- Defines the surface pressure surface temperature
               and the 2D grid of path delay through the neutral atmosphere.

    The file contains only onre record of the fesit seven tpyes and usually 
    more than one record of DEL_REC. Each DEL_REC corresponds to one time 
    epoch. The time epochs follow each other in chronological order with
    the same time step, without gaps. The time epoch of a specific DEL_REC
    is determined bny its index in the file, time of the first epoch, and
    the time step.

    Decription of individual records:

    LAB__REC 
           CHARACTER  PREF*8     ! prefix: LAB_REC 
           INTEGER*8  LEN        ! length of the LAB_REC record
           CHARACTER  FMT_LAB*40 ! Format label
           INTEGER*8  OFF_TIM    ! Offset of the TIM record in bytes wrt the file beginning      
           INTEGER*8  OFF_STA    ! Offset of the STA record in bytes wrt the file beginning      
           INTEGER*8  OFF_MOD    ! Offset of the MOD record in bytes wrt the file beginning      
           INTEGER*8  OFF_MET    ! Offset of the MET record in bytes wrt the file beginning      
           INTEGER*8  OFF_ELV    ! Offset of the ELV record in bytes wrt the file beginning      
           INTEGER*8  OFF_AZM    ! Offset of the AZM record in bytes wrt the file beginning      
           INTEGER*8  OFF_DEL    ! Offset of the first TIM record in bytes wrt the file beginning
           INTEGER*8  LEN_TIM    ! Length of the TIM record in bytes
           INTEGER*8  LEN_STA    ! Length of the STA record in bytes
           INTEGER*8  LEN_MOD    ! Length of the MOD record in bytes
           INTEGER*8  LEN_MET    ! Length of the MET record in bytes
           INTEGER*8  LEN_ELV    ! Length of the ELV record in bytes
           INTEGER*8  LEN_AZM    ! Length of the AZM record in bytes
           INTEGER*8  LEN_DEL    ! Length of the DEL record in bytes
	   INTEGER*4  TOT_NUM_DEL ! The number of DEL records

    TIM_REC
           CHARACTER  PREF*8     ! prefix: TIM_REC 
           INTEGER*8  NREC       ! The number of time epochs the file contains
	   INTEGER*4  MJD_BEG    ! Modified Julian date at TAI     ! Modified Julian date at TAI for the first epochfor the first epoch
	   INTEGER*4  MJD_END    ! Modified Julian date at TAI for the last epoch
	   REAL*8     TAI_BEG    ! TAI for the first epoch. Units: seconds
	   REAL*8     TAI_END    ! TAI for the last epoch. Untis: seconds
	   REAL*8     TIM_STEP   ! Time step. Units: seconds

    STA_REC
           CHARACTER  PREF*8     ! prefix: STA_REC 
           CHARACTER  NAME*8     ! Station name. NB: the station name does NOT necessarily
                                 ! controrms any convention. It may be an arbitrary combination
                                 ! of characters. Parser software should NOT assign any meaning 
                                 ! to this field
	   REAL*8     COO_CFS(3) ! Station coordinates in the crust-fixed coordinate system.
                                 ! Units: meters
	   REAL*8     PHI_GCN    ! Station geocentric latitude. Units: radians
	   REAL*8     PHI_GDT    ! Station geodetic latitude. Units: radians
	   REAL*8     HEI_ELL    ! Station height above the reference ellipsoid. Units: meters
	   REAL*8     HEI_GEOID  ! Station height above the geoid. Units: meters

    MOD_REC
           CHARACTER  PREF*8     ! prefix: MOD_REC 
	   INTEGER*4  N_RFR      ! Number of components of the model
	   CHARACTER  SPD_TYPE(3)*8 ! Array of names of the slanted path delay model components.
                                    ! Supported values: 
                                    !   total    -- Total path delay through the neutral atmosphere
                                    !   hydro    -- Path delay through the hydrostatic component of the atmosphere
                                    !   non-hydr -- Path delay through the non-hydrostatic component of the atmosphere
                                    !   undef    -- Undefined, not used
           INTEGER*8  N_LINES       ! Number of lines with model description
           INTEGER*8  LEN_TEXT      ! Length of the text with model description in bytes
           CHARACTER*1, POINTER :: TEXT(:) ! Text with the model description as a string that contains \n characters 
                                           ! of length LEN_TEXT + 1 (the last character is \0)
    MET_REC
           CHARACTER  PREF*8     ! Prefix: STA_REC 
           INTEGER*8  N_LINES    ! Number of lines with numerical weather model description
           INTEGER*8  LEN_TEXT   ! Length of the text with teh numerical model description in bytes
           CHARACTER*1, POINTER :: TEXT(:) ! Text with the numerical weather model description as 
                                           ! a string that contains \n characters of length 
                                           ! LEN_TEXT + 1 (the last character is \0)
    ELV_REC
           CHARACTER  PREF*8     ! Prefix: ELV_REC
	   INTEGER*8  N_EL	 ! The number of elements along the elevation angle axis
	   REAL*4,    POINTER ::   ELEV(:) ! Array of elevation angles. Dimension: N_EL, 
                                           ! Units: radians. Array is sorted in decreasing order.
    AZM_REC
           CHARACTER  PREF*8
	   INTEGER*8  N_AZ       ! The number of elements along the azimuth axis
	   REAL*4,    POINTER ::   AZIM(:) ! Array of azimuth angles. Dimension: N_AZ, 
                                           ! Units: radians. Array is sorted in increasing order.
    DEL_REC
           CHARACTER  PREF*8
	   REAL*4     SURF_PRES  ! Surface pressure. Units: Pascal
	   REAL*4     SURF_TEMP  ! Surface air temperature. Units: Kelvin
	   REAL*4,    POINTER ::   DEL(:,:,:) ! 3D array of slanted path delay components. 
                                              ! The first  axis runs over elevation angles.
                                              ! Dimension: N_EL defined in ELV_REC
                                              ! The second axis runs over azimuth angles
                                              ! Dimension: N_AZ defined in AZM_REC
                                              ! The third  runs over components.
                                              ! Dimension: N_RFR defined in MOD_REC
                                              ! Units: seconds

17) IONOSPHERE_DATA_FILE:           
=========================
    Label:   VIONO Little-Endian  Format of 2010.05.08       
    Purpose: Contains the total electron contents of the ionosphere
             presented at the regular 3D grid with axes: longitude,
             latitude, and time.
             
             
    Type:    Binary, little endian
    Example: http://astrogeo.org/viono/codg_01.vio 

    Format description:

    The file in VIONO format consists of the header record and one 
    or more data records.

    HEADER:
            CHARACTER  LABEL*48   ! File label
            CHARACTER  MODEL*16   ! Model name
	    CHARACTER  AUTHOR*16  ! Name of the model author
	    INTEGER*4  NLON       ! The number of grid steps along longitude axis
	    INTEGER*4  NLAT       ! The number of grid steps along latitude axis
	    INTEGER*4  NEPC       ! The number of grid steps along time axis
	    INTEGER*4  MJD_BEG    ! MJD at TAI of the first epoch
	    INTEGER*2  MISSING    ! Missing value
	    INTEGER*2  FILLER(3)  ! fillers
	    REAL*8     UTC_BEG    ! UTC Time tag of the first epoch. Units: seconds
	    REAL*8     TIM_STEP   ! Time step along the time axis. Units: seconds
	    REAL*8     SCALE      ! The scaling factor which should be applied to raw TEC values. Units: TECU
	    REAL*8     LON_MIN    ! Longitude at the beginning of the longitude axis. Units: radians
	    REAL*8     LAT_MIN    ! Latitude  at the beginning of the latitude  axis. Units: radians
	    REAL*8     LON_STEP   ! Longitude step along the longitude axis. Units: radians
	    REAL*8     LAT_STEP   ! Latitude  step along the latitude  axis. Units: radians
	    REAL*8     HEIGHT     ! Height of the ionosphere. Units: meters

    DATA RECORD:
            INTEGER*2, POINTER :: TEC_VAL(:,:) ! TEC values on a 2D longitude/latitude grid.
                                               ! Dimenstions: NLON,NLAT. Units: dimensionless

    TEC_VAL array must by miltiplied by SCALE. Units of the results: TECU.


18) HYDROSTATIC_MAPPING_FUNCTION:  (MMF)
========================================
    WET_MAPPING_FUNCTION:          (MMF)
    WET_ZENITH_DELAY:              (MMF)

    Label:   # MMF_MOD   Format of 2008.09.21
    Purpose: contains coefficients of polynomials that expand the mean
             mapping function in the neutral atmosphere for the set 
             observing stations.
    Example: $(VTD_ROOT)/share/mmf.mod

    A file in MMF_EPO format consists of records of variable length
    in ASCII coding. The records are separated by a character with decimal
    code 13. The records are grouped into sections. Sections follow
    in this order:
  
    1) Header record -- the first record should have a signature:
                        TROPO_PATH_DELAY  Format version of 2007.10.04
     
                        The header record allows to distinguish a valid
                        file in the TROPO_PATH_DELAY  format from files
                        in other formats.
     
    2) M-record section
       M-record  has letter M in the first field. The M record keeps the
                 model identifier.
     
    3) N-record section
     
    4) S-record section
     
    5) D-record section
     
    6) Trailer record -- the last record is the same as the header record.
     
     
    Format of an S-record:
    ----------------------
     
    Field  1:1   A1    -- Record ID. Should be letter S (decimal code 83).
    field  2:2   a1       delimiter: blanks.
    Field  4:11  A8    -- 8-letter long site identifier. May contain
                          any characters with decimal codes 32-255, but
                          blanks are allowed only at the end of the site
                          identifier. This site identifier should be unique
                          among S-records. This field should not
                          necessarily have a special meaning. Parsing
                          software should not try to interpret it.
    field 12:13  a2       delimiter: blanks.
    Field 14:26  F13.4 -- X site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 27:27  a1       delimiter: blank.
    Field 28:40  F13.4 -- Y site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 27:27  a1       delimiter: blank.
    Field 42:54  F13.4 -- Z site coordinate in a crust fixed reference
                          frame. Units: meters.
    field 55:56  a2       delimiter: blanks.
    Field 57:64  F8.4  -- Site geocentric latitude, positive to north,
                          in degrees. This field is for information only.
                          Parsing software MUST ignore it.
    field 65:65  a1       delimiter: blank.
    Field 66:73  F8.4  -- Site longitude, positive towards east,
                          in degrees. This field is for information only.
                          Parsing software MUST ignore it.
    field 74:74  a1       delimiter: blank.
    Field 75:80  F6.1  -- Site height above the reference ellipsoid in
                          meters. This field is for information only.
                          Parsing software MUST ignore it.
                                                   
