PDS_VERSION_ID           = PDS3
RECORD_TYPE              = STREAM
SPACECRAFT_NAME          = "PHOBOS_2"
OBJECT                   = TEXT
 NOTE                    = "Description of the GEOMETRY directory contents"
 PUBLICATION_DATE        = 1998-08-2
END_OBJECT               = TEXT
END



               GEOMETRY directory contents


The GEOMETRY directory contains coordinate files for the ISM sessions,
and altimetric contours files for Mars and Phobos used by the mapping
routines.

All these files are in binary format, except where indicated. Their detailed 
format is described in labels contained in the directory /Label (Mar_coor.lbl 
and Pho_coor.lbl).
The following files are found in this directory:



1. Coordinates and angles for ISM Mars sessions

 XXX_COOR.DAT, where XXX is the nickname of the session (11 files)

Coordinates and angles are computed by "Coord.for" from orbital parameters
and instrument characteristics. Longitude and latitude of the four pixel
corners are given in sequence. Longitudes are given using the terrestrial
convention (-180 to 180 degrees eastward) to allow representation as 16-bits
signed integers. Incidence and emergence angles are given relative to the
average normal (direction of Mars' center).
The coordinates contained in these files are computed for the second order,
even, channels, and can be used for all practical purpose; coordinates
corresponding to the other detector arrays can be computed using "Coord.for"
(uncomment the corresponding lines in the source program).
The files are used in particular by Pixtrace.for and IDL_map.pro to plot maps
of spectral ratios.


2 Coordinates and angles for the main Phobos image cube

		Pho_coor.dat 	Geographic coordinates and angles for Phobos. Used by
                 ISM_pho.pro
		Pho_scor.dat 	Screen coordinates and angles for Phobos, exact pixel shapes.
		Pho_scrn.dat 	Screen coordinates and angles for Phobos, coordinates are
                 adapted to get adjacent pixels and continous maps. Used by 
                 ISM_map.pro.
		Pixloc.ctr 		 Screen coordinates of pixels centers in the plane
                 perpendicular to the line of sight, regardless of whether 
                 they are on the disk or not. Distances are given in 
                 kilometers from the center of Phobos.

Geographic coordinates are given according to the terrestrial convention
(longitude ranges from -180 to 180 degrees eastward). Incidence and emergence
angles are computed relative to the local normal, as computed from T.
Duxbury's model of Phobos (1991); their values are probably not very accurate
near the limb. Phase angle is estimated from its average value, movement of
the spacecraft, and position of the entrance mirror, and is not only
indicative (see description of the geometry of observation in "DocISM.pdf").


3. Altimetric contours for Mars

 Mars%%h.dat     where %% ranges from 08 to 23

These files contain altimetric contours hand-digitized from the Mariner 9
altimetric map of Mars. They are used by Pixtrace.for to superimpose Martian
contours to the ISM maps.


4. Reference contours for Phobos

 Gricor.dat
This file contains reference contours from T. Duxbury's 1991 model of PHobos.
It is used by Photrace.for to superimpose a contour to the ISM maps of Phobos.