MOLA 128 Polar files in GIS format

Converted from the files MOLA DEMs 'megt_n_128_1.img, megt_s_128_1.img' from
the MOLA PDS website: http://pds-geosciences.wustl.edu/missions/mgs/megdr.html
on Jan 2005.

They were converted to an ISIS file to calculate the correct projected meters
offset which was not available in the original labels using lev2lab. Then they
were converted to a 32bit ESRI (Arc/Info,ArcView) Grid format from the original
unsigned 16bit PDS images using the scale and offet values found in the PDS label.
>new_image32 = orig_image16 * 0.25 + -8000

ISIS calculated cell size in meters: 460.35786
Note: Circular latitude range (~ +-51.51 to +-90)


Projection Note:
You will want to force programs that support elliptical equations for polar
stereographic to use the semi-minor axis '3376200.0' for both axis. ISIS now
(sincce 2004) uses the semi-minor axis for its polar projection ('pola') also.


Grid projection file 'prj.adf' for the north (-90lat true scale for south):
Projection    Polar Stereographic
Units         METERS
Zunits        NO
Xshift        0.0
Yshift        0.0
Parameters    3376200.0  3376200.0 /*Semi-minor radius of Mars
   0  0  0.0 /* longitude of central meridian
  90  0  0.0 /* latitude of true scale
0.0 /* false easting (meters)
0.0 /* false northing (meters)


ArcMap projection definitions:
Copy the file 'Mars Spolar Sphere.prj' and 'Mars Npolar Sphere.prj' to your
ArcMap fovrites folder to define your dataframe's coordinate system. This directory
is usually found:
C:\Documents and Settings\USERNAME\Application Data\ESRI\ArcMap\Coordinate Systems\

ArcMap/ArcInfo Projection Information for the Grids:
I have supplied a 'prj.bak' file in the data's directory but it will need to be
renamed from prj.bak to prj.adf. With no projection set for the data file, ArcMap
will not try to do anything fancy using its projection-on-the-fly enigne for
rasters. If you rename this file to prj.adf and set the projection correctly for
the ArcMap's dataframe, this shouldn't be an issue and you can use images that
have their projection define.

How to convert to another format:
The ESRI grid format can be converted to many other GIS/RS formats using the
opensource library GDAL utility called 'gdal_translate' on most machine types.
The file to convert is the 'w001001.adf' example:
>gdal_translate -of gtiff megt_n_128_1\w001001.adf megt_n_128_1.tif



Trent Hare
USGS, flagstaff
thare@usgs.gov
928-556-7126