2025.09.24
               Bug fixes release

2025.09.06
               a) Added support of SP3c format for ephemeride of GNSS 
                  satellites

               b) Added support of TLE format for ephemeride of Earth
                  orbiting satellites
               
               c) Added a new format of source positions. It allows to
                  specify source positions in two ways: fixed right 
                  ascension and declination for galactic or extragalactic
                  objects and ephemeride for near zone objects. The 
                  ephemerides in four formats are supported:
                  -- NZO
                  -- CCSDS ODM
                  -- TLE
                  -- SP3c
                  In a latter case a direcotry with one or more ephemeride
                  files following in the chronological order is specified.

                  The new format has label # SOURCE-NAMES  v 3.0 2025.09.06
                  See vtd_formats.txt for format description.

               d) Replaced keyword PHASE_OFFSET_FILE with DIR_BTX. VTD now 
                  does not ingest antenna phase center offset file directly, 
                  but requires to convert it to a set of binary data files 
                  in BINTEX format, one file per antenna. DIR_BTX keyword 
                  defines directory name where these files are located.

               e) Added utility vtd_antex_to_bintex that parses a file with 
                  phase center offsets for both space-born satellite 
                  and ground antennas, mainly for GNSS observations, splits 
                  the data, and writes into output files in binary BINTEX 
                  format.

2025.06.22
               a) Added progran stapos_to_bin that processes 
                  a directory with files in ascii station position 
                  evolution format and tranforms each of them
                  to the binary BINDSIP station displacement format,
                  so VTD can load them.

2025.03.28     a) Made an additional update in vtd_apriori.py to 
                  better treat processing merged mass loading

               b) Updates in difxvtd related to correlation of
                  VLBI observations of GNSS satellites.
                  (Joe Skeens).

2024.11.27     a) Updated vtd_apriori.py
                  Directories with slant path delays created before are
                  not compatible. They should be removed before the 
                  first use of vtd_apriori.py

2024.09.12     a) Updated phase feed rotation tracking for satellites to
                  preserve the continuity (+/- 2pi radians) of 
		  differential feed rotation (aka windup) rather than 
                  tracking individual feed rotation values by antenna.
                  (Joe Skeens).

               b) Simplified the feed rotation vector primitives to
                  agree with the formalism to be published in an 
		  upcoming paper (Joe Skeens).

2024.05.11     a) added support of antenna and source phase
                  center variations in data reduction.
                  Added a keyword PHASE_OFFSET_FILE
                  Old VTD configuration files need be 
                  updated using vtd_control_update tool. 

               b) Implemented data reduction for phase center 
                  offset and its variations (satellite and receiver), 
                  as well as carrier phase windup in the calculation 
                  of the geometric delay. Phase center offset is 
                  implemented as a receiver position shift, and 
                  phase center variation and carrier phase windup
                  are implemented as delays.

               c) Added a new MOUNT_TYPE GNSS. For that type of 
                  antennas, phase center variation according 
                  to definitions from the file specified in the
                  keyword PHASE_OFFSET_FILE is computed
                  instead of antenna axis offset.

               d) Updated the algorithm for computation 
                  of the interferometric polynomial in 
                  dfx2fits -- the old version can accumulated 
                  noticeable errors due to rounding.
                 

2023.12.23     a) added support of computation of path delay for 
                  Earth orbiting satellites

               b) Added option --missing for vtd_apriori_update.py
                  that checks for missing static apriori. 
                  It updates the specified file only if it is missing

2023.03.14     a) Added support of a priori proper motions and parallaxes
                  for computation of path delay. Added new keyword
                  SOURCE_PRLX_PRP_MOTION in the VTD control file
                  for specifying a priori proper motions and/or
                  parallaxes used for path delay computation.
                  The format of the a priori file is described
                  in doc/prlx_prp_format.txt
                  
               b) Made a change: Galactic aberration is not computed
                  for objects with non-zero a priori parallaxes.

2022.10.01        JPL planetary ephemeride was upgraded to de440.
                  The older ephemeride files are not supported.
                  VTD control files should be updated to point to
                  ephemeride file de440. The de440.eph file 
                  distributed with VTD is valid for 1970-2070 time
                  range.

2022.08.30     a) Added support of IONOSPHERE_SCALE control file keyword.
                  The ionospheric contribution computed from TEC maps
                  is multiplied by that parameter.
               b) Added support of SOU_DEBIAS_MODE control file keyword.
                  It specifies the name of the source position de-bias 
                  model. It is for compensation of the source position 
                  bias caused by the the deficiency of an ionospheric 
                  model or other models. The contribution of the de-bias 
                  model to path delay is computed on the basis of an 
                  empirical model that describes the position bias
                  in declination as a function of declination. Supported 
                  models: MOD1 and MOD2.

2021.04.30     a) Added computation of W-projection of the baseline vector
               b) Added accounting for aberration in computation of  uvw
                  baseline vector projections
               c) Added difxvtd utility for computation of the path delay
                  for the DiFX correlator.

2020.11.05     a) now when source structure path delay is computed,
                  correlated flux density is computed as well and 
                  is available as DER_DEL(VTD__COR_FD1) and 
                  DER_DEL(VTD__COR_FD2) for high and low frequencies.

2020.03.22     a) Added  support of CAPITAINE_2005 precession expression.
               b) Added support of MEAN_POLE_MODEL keyword. Supported
                  values: NONE, IERS2010, IERS2022.
               c) keyword MPL_FILE is removed.
               d) Undated vtd_control_update so it upgrades old VTD.
                  controls of format revision 2019.03.03 to the current
                  format revision.
               e) Added option -d (--download) in vtd_apriori_update.py
                  This option removes the old local VTD a priori files
                  and downloads them from the remote server instead
                  of upgrade. This option has to be used when the number
                  of sites with a priori loading and slant path delay is
                  changed at the remote server.
               f) Added support of dowloading harmonic vairaitons of
                  site position displacements caused by loading 
                  in vtd_apriori_update.py . Support of two new mnadatory
                  keywords is added in vtd_apriori_update.py
                  HPS_URL:
                  LOAD_HPS_DIR:
               g) Extended read/write locks in vtd_apriori_update.py 
                  for ionosphere TEC maps and slant path delay.

2019.10.13     Fixed a bug in bindisp_merge related to locking.
               
               Changed name of lock files.

2019.09.15     Enabled handling read/write locks in vtd_apriori_update.py 
               to prevent crashing software that reds loadings during
               update time:
           
               Added support one new source catalogue format
               #  Source position file format  1.0  of 2019.08.08

               Fixed several bugs related to configuration with curl.

2019.05.25     Added vtd_apriori_update.py program for automatic
               downloading ephemeral a priori: the Earth 
               orientation parameters, expansion coefficients
               of the ionosphere contribution, time series of 
               3D crustal deformations caused by mass loading,
               and the expansion coefficients of slant path 
               delay.

               Fixed a long-standing bug related to handling
               locks when loading mass loading displacements.

               Added ./reconfigure command that re-runs stored
               configuration. ./reconfigure -d displays the last
               configuration.

               Forced shell intermediate files, for instance object
               files created by the compiler be group readable and 
               group writable. Forced make invoke shell bypassing
               startup scripts which made running make significantly 
               faster.

               Added support of environment variables in VTD control 
               file. Format: ${VAR_NAME}, where VAR_NAME is an 
               environment variable. VTD expands the environment 
               variable at any occurrence of the control file.
               Nested environment variables are supported.

               Added setting stack size and environment
               variable GOMP_STACKSIZE on start-up of executables.
               That eliminated necessity to setup stackszie and
               GOMP_STACKSIZE to avoid a crash during loading
               the executable.

               Added document vtd_apriori_update.txt (and .html)
               in doc/ directory.

2019.04.04     Fixed examples. 
               Fixed VTD_LOAD to prevent a crash in the attempt to 
               compute solid tides displacement for an orbiting
               radiotelescope.

2019.03.03     Added support up to 9 ionosphere TEC map files.

2018.10.15     Added support --with-curl configure option.
               cfitsio-3.42 and newer may be compiled with 
               curl support, and in that case VTD needs be 
               linked against curl.

2018.06.30     Made a change needed to be compatible with 
               ners-20180628 related to computation of 
               accumulated secular term in nutation.

2018.05.31     Added support of value NERS for EOP_TIME_SCALE, 
               UZT_MODEL, UZT_USE keyword in the control file.
               Thus, when NERS is used, VTD control file should
               have these definitions:
              
               LEAP_SECOND:             NERS
               EOP_SERIES:              NERS
               EOP_TIME_SCALE:          NERS
               UZT_MODEL:               NERS
               UZT_USE:                 NERS
               HARMONIC_EOP_FILE:       NERS
               PRECESSION_EXPRESSION:   NERS
               NUTATION_EXPANSION:      NERS
               EROT_COMPAT:             NONE
               GEODESIC_NUTATION:       NONE

               Fixed several bugs related to gfortran 8.1


2018.04.04     Added utility bindisp_merge for merging loading binary files

               Fixed support of NERS

2017.12.27     Added support of value NERS for the keyword LEAP_SECOND.
               LEAP_SECOND: NERS will force VTD to download the table 
               of leap seconds using the default NERS configuration file.

2017.10.27     Fixed a regression bug in the previous release that 
               prevented installation.

2017.10.17     Added computation of group delay and delay rate with 
               respect to geocenter for the 1st and the 2nd
               station of a baseline. These parameters are placed
               in DEL_DEL and DEL_RAT arrays.

2017.05.15     a) Fixed errors related to computation of source structure
                  delays.

               b) Fixed bugs in the installation procedure.

               c) Fixed regression bug in vtd_example_03

2016.11.17     Added support for NERS (Network Earth Rotation Service).
               NERS retrieves the Earth rotation parameters from
               the NERS server automatically. Thus, there is no need
               to refresh the Earth rotation series manually.
               To set the NERS, the following five parameters are
               specified:

               AEM_FILE:                NONE
               ERM_FILE:                NONE
	       EOP_SERIES:              file
               PRECESSION_EXPRESSION:   NERS
               NUTATION_EXPANSION:      NERS

               where file is the name of the NERS client configuration
               file.

               Keyword HARMONIC_EOP_FILE supports a special value:

                       HARMONIC_EOP_FILE:       NERS

               in that case the harmonic Earth orientation variations
               are taken from the Network Earth Rotation Service.

               VTD now depends on ners library.

2016.08.30  a) Added support for BWG (beam waveguide) antennas.
               For computing axis offset, the BWG antennas are the
               same as AZEL, however the feedhorn rotation angle
               for BWG antennas is different than for AZEL.
               Added support of alias for NASR (the same as NASP)
               for Nasmyth right-handed mounting and NASL 
               (the same as NASL) for Nasmyth left-handed mounting.

            b) Added support for NERS EOP time series


2016.02.17  a) Added partial derivative over relativistic parameter
               Gamma for VLBI observations

            b) Added generation of the file with definitions of
               environment variables for bash shell as well.
               The have names vtg_vars.sh and export_vtd_vars.sh


2015.08.07     changed BINDISP format of file with station 
               displacements: extended the header.


2014.08.20  a) Added support of a new keyword 
               ATMOSPHERE_PATH_DELAY_PARTIAL. In the previous
               version the role of partial derivative of
               atmosphere path delay in zenith direction played
               WET_MAPPING_FUNCTION. In the new version
               WET_MAPPING_FUNCTION is used only for computing
               a priori path delay.

            b) Added new qualifiers of ATMOSPHERE_PATH_DELAY_PARTIAL:
	       partial derivative of path delay with respect to
               atmosphere path delay in zenith direction played

               -- TOTAL_SCALE    -- partial derivative is equal 
                                    to the ratio of slant path
                                    delay to the path delay in
                                    zenith direction

               -- WATER_SCALE    -- partial derivative is equal 
                                    to the ratio of water vapor 
                                    component of slant path delay 
                                    to the water vapor component of
                                    path delay in zenith direction

               -- GAUSSIAN_LAYER -- partial derivative is defined
                                    for the model when the dependence of 
                                    concentration of residual atmosphere 
                                    with height is described as a Gaussian
                                    function with the specified mean
                                    (i.e. layer height) and the specified
                                    full width half maximum (FWHM). The 
                                    height of the layer is specified in 
                                    the 3rd qualifier and the FWHM is 
                                    specified in the 4th qualifier.

            c) Added new program vtd_control_update that automatically
               converts the specified control file in the old format to 
               the current format.
                                    
2014.06.29     Added support of multiple slant path delay 
               that define delays for the same station for
               different ranges of epochs

2014.04.04     Added support of MAC OS (Darwin) operating system.

2014.02.18     Made changes in dealing with external atmosphere 
               path delay to support the new data format.

2013.09.30  a) Added support of new mountings NASM and NASP
               (Nasmyth minus and Nasmyth plus, f.e. YEBES40M).
            b) Added support of feed horn angle computation for
               antennas with EQUA, X-YE, NASM, NASP mounting
               type.
            c) Added parameter FEED1 and FEED2 in DER_DEL array.
            d) VTD now correctly computes path delay for
               antennas with mounting types EQUA, X-YE, NASM
               and NASP.
            e) Changed form of station description file and 
               added column antenna diameter.

2013.02.08  a) Fixed installation bug: vtd checked wrong header
            b) Fixed a typo in fitslib library header
            c) Fixed an uninitialized variable bug which may
               cause a crash segmentation fault


2012.11.29  a) Fixed installation bug that did prevent installation
               of vtd_example_06.
            b) Added support of EROT_COMPAT NO_SARG argument.
               If this option is set, then UT1 and polar motion
               are set to zero regardless values EOP files.
               This may be needed for testing.
            c) Fixed a bug: library so-name was incorrectly
               set to libfitio.so.1 instead of libfitlib.so.1

2012.11.25  a) Added support of a case when one of the 
               stations is on the orbit
            b) Added routine for computation of light
               time between the orbiting and downlink
               station.


2010.06.20  a) Added support of ionosphere path delay.
            b) Added support of slanted path delay biases.
            c) Added C-language bindings
            d) Improved documentation. Added two new documents: 
               Formats of a priori files for VTD and
               VTD a priori files management
            e) Increased VTD__NDER.

2009.05.30  a) Added support of the contribution of slanted path delay
               in the neutral atmosphere.
            b) Added support for antenna thermal deformation.

2008.05.02  a) Added support of two new keywords in the control file:
	       ANTENNA_THERMAL_DEFORMATION, GALACTIC_ABERRATION.
            b) renamed EXTERNAL_PATH_DELAY_FILE to EXTERNAL_DELAY_DIR
            c) added keywords EXTERNAL_DELAY_DIR_2ND, EXTERNAL_DELAY_DIR_3RD
               EXTERNAL_DELAY_DIR_4TH
            d) added keywords SOURCE_COORDINATES_2ND, 
               SOURCE_COORDINATES_3RD, SOURCE_COORDINATES_4TH



2007.06.18  a) Added support of three new keywords in the control file:
               ANTENNA_DEFORMATIONS_FILE, EXTERNAL_PATH_DELAY_FILE,
               PARALLACTIC_ANGLE
            b) Added computed of reduction for the feed-horn rotation
            c) Added support of reduction for source structure
            d) Fixed examples
            e) Updated documentation

2007.01.11  a) Renamed VTD_DO to VTD_DELAY.
            b) Added new parameter DOPPLER_EXPR in the control file.
            c) Added new routine VTD_DOPPLER for computation of the 
               Doppler frequency shift.
            d) Added vtd_example_02 and vtd_example_03.
            e) Updated documentation.
            f) Fixed a minor error in the routine for computation of the 
               time delay for near zone objects.
