   Specifications of MMF_EPO format.
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

   MMF_EPO format is for distribution the mean mapping function in the neutral
   atmosphere for the set of epochs for a given set of stations.

   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.
