OBJECT                            = DATA_SET_MAP_PROJECTION
 DATA_SET_ID                      = "MRO-M-SHARAD-5-3D-V1.0"

 OBJECT                           = DATA_SET_MAP_PROJECTION_INFO
  MAP_PROJECTION_TYPE             = "TRANSVERSE MERCATOR"
  MAP_PROJECTION_DESC             = "

For this ellipsoidal cylindrical projection [SNYDER1987], the axis of the 
cylinder lies in the equatorial plane and the line of tangency is any chosen 
meridian. For the midlatitude SHARAD 3D radargrams, the central meridian 
(longitude) and central latitude are chosen within or near the area of 
interest. The ellipsoid has an equatorial radius of 3,396,000 meters and a 
polar radius of 3,376,000 meters. A central scale factor of 0.9996 is applied, 
and a false easting of 2,000,000 and a false northing of 2,000,000 are added 
to maintain positive X and Y coordinates.

SHARAD observations input to the 3D processing are provided with along-track
information (see GEOM files in the SHARAD US PDS RDR archive) that includes
east longitudes and planetocentric latitudes. The 3D processing procedures
are carried out in cartesian space, so the locations for the midlatitude data 
were first transformed to this Transverse Mercator projection. The IDL 
procedures MAP_PROJ_INIT and MAP_PROJ_FORWARD were used for this 
transformation, specifying the GCTP projection 109 as well as Mars semimajor 
and semiminor axes as noted above. The data label files list the 
CENTER_LONGITUDE and CENTER_LATITUDE values used for each dataset. Given the 
planetocentric latitudes, this ellipsoidal projection was not an ideal choice. 
Nevertheless, accurate longitudes and planetocentric latitudes can be obtained 
by inverting the projection using this same ellipsoid (e.g., using IDL's 
MAP_PROJ_INVERSE).

For the transformations between line and sample coordinates and planetocentric 
latitude and longitude coordinates, the reader is referred to [SNYDER1987]."

  ROTATIONAL_ELEMENT_DESC         = "See [SEIDELMANNETAL2002]."

  OBJECT                          = DS_MAP_PROJECTION_REF_INFO
   REFERENCE_KEY_ID               = "SEIDELMANNETAL2002"
  END_OBJECT                      = DS_MAP_PROJECTION_REF_INFO

  OBJECT                          = DS_MAP_PROJECTION_REF_INFO
   REFERENCE_KEY_ID               = "SNYDER1987"
  END_OBJECT                      = DS_MAP_PROJECTION_REF_INFO

 END_OBJECT                       = DATA_SET_MAP_PROJECTION_INFO
END_OBJECT                        = DATA_SET_MAP_PROJECTION