MEGDR PDS Topography GIS header files for ArcMap and ERDAS
Sep 16, 2003

The latest MEGDR product is version "b" (May 7, 2003), a near-global
topographic map at 1/128 degrees per pixel. It covers latitudes
from 88 north to 88 south and the full longitude range. As a single
image the  map would be about 2 gigabytes in size, so it is divided
into 16  tiles for ease of handling. Each tile is stored as a
separate image  file with a detached PDS label in another file with
the same name, extension ".LBL". The tiles can be used alone or
reassembled to make the global map. Each tile covers 44 degrees in
latitude and 90 degrees in longitude. The maps are in simple
cylindrical (equidistant cylindrical) projection using the IAU2000
planetocentric coordinate system with east positive longitude.

Download the PDS images and labels from:
http://wufs.wustl.edu/missions/mgs/mola/megdr.html
Download the GIS Headers from:
ftp://webgis.wr.usgs.gov/mars/mola/megt128PDS_GISheaders_Erdas_ArcMap.zip

Instructions:
1.) unzip the file megt128_gis_headers_Erdas_ArcMap.zip into the same
  directory as the *.img files. This will uncompress *.raw and *.rww
  for each file. The ERDAS header *.raw file points to the *.img and
  the *.rww is the worldfile.

These now have the correct information to be read into GIS programs and
other program like ArcMap and ERDAS Imagine. For more ESRI raw headers,
which will allow ArcView 3.x, ENVI, Global Mapper, OpenEV, and other
programs the ability to read these files download:
ftp://webgis.wr.usgs.gov/mars/mola/megt128PDS_GISheaders_other.txt

The GIS header files are defined with a center longitude of 180.
Although the names are for the topography files, other datasets like
planetary radius, areoid, and counts can be used by just renaming the
files.

These were generated from the PDS labels. Note, the MOLA labels truncate
the major-axis to 3396.0 and use the same value for the minor axis.
ISIS defines Mars as 3396.19 and 3376.2 km for the Semi-major and
minor axis. This will generate a slightly different km/pixel value 
(than ISIS generated labels), which will also change the X, Y values
calculated in the world files. Thus if using other data created in
ISIS use the world files from: megdr128_gis_header_files_ISIS.zip
ftp://webgis.wr.usgs.gov/mars/mola/megt128ISIS_GISheaders_Erdas_ArcMap.zip

These files were written out by the PERL program pds2world.pl
from the MEGDR Version b: 1/128 pixels per degree labels. This
PERL script can be downloaded from:
http://webgis.wr.usgs.gov/perl.htm

Example run:
>foreach i (*.lbl)
>perl pds2world.pl -e $i
>end


Trent Hare
USGS, Flagstaff
thare@usgs.gov
