hitchner@riacs.edu (Lewis Hitchner) (01/24/91)
NASA Ames' Visualization for Planetary Exploration project
Mars Viking data sets
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[Note:
In the request from dirtybob@blake.u.washington.edu he made
reference to a NASA presentation he saw at the Smithsonian. I am
not familiar with NASA's Smithsonian exhibit, though my guess is that
it includes JPL's "Mars, the Movie" animation. To my knowledge the
data set JPL used for "Mars, the Movie" is not publically available
(we have not yet obtained it ourselves, though we have a contact to
get it for us whom we are working with). The only reason that's
it's not available, I think, is just that it has not been processed
and documented for public release, whereas the Viking data sets we
have have been extensively processed by the USGS, documented (sort
of), and installed in NASA's space data archives. It is too bad the
same hasn't been done with the data set used in "Mars, the Movie",
as the satellite imagery used for texture mapping is full color,
whereas the imagery we have available for texture mapping is gray
scale only.]
National Space Science Data Center
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There are two Mars data sets we are using. They are both available
from NASA's NSSDC (Natl. Space Science Data Center), which is located
at NASA Goddard Space Flight Center (GSFC -- get ready for a lot of
acronyms!):
National Space Science Data Center
Goddard Space Flight Center
code 633.4
Greenbelt, MD 20771
301-286-6695 (FTS 888-6695)
Mars Viking DTM Data
--------------------
The main data set is the digital terrain elevation values. These are
called DTM's (Digital Terrain Model) by the USGS. You should request
the "Viking Digital Terrain Model" data set, NSSDC tape numbers:
FLG014 - 1 file, North 60 deg. of latitude
FLG015 - 1 file, Central (Equatorial) 60 deg. of latitude
FLG016 - 1 file, South 60 deg. of latitude
FLG013 - 4 files of whole planet at subsampled resolutions
The full resolution data set files are Sinusoidal Equal Area
projections of the digital elevations with a spatial sampling interval
of 1/64 degree of latitude per pixel (about 926 meters/pixel). The
elevation data is in meters measured as 16 bit unsigned ints (shorts),
though the accuracy of the elevation values is no where near 1 meter.
The DTM data was derived via stereo-pair photogrammetric processing
from Viking Orbiter digital images by the USGS in Flagstaff, AZ. The 3
full res. data tapes total approx 484 MBytes of data, and there is
another 11 MBytes on the tape with the subsampled images. All tapes
are distributed as 6250 bpi 9 track magetic tapes (same for DIM tapes,
below). Cost is zero to qualified organizations (e.g., other govt.
agencies, educational institutions, etc. -- I think commercial users
might have to pay something) except that you must return either the
original tapes or blank reels to NSSDC.
Mars Viking DIM Data
--------------------
The second data set we are using is processed Viking Orbiter digital
imagery that can be used for texture mapping (because it has been
processed into a Sinusoidal Equal Area projection, and, thus, can be
registered with the DTM data, though it requires some processing to do
so). These are called DIM (Digital Image Model) data sets by the
USGS. You should request the "Mars Medium Resolution Mosaic Digital
Image Model" data set, NSSDC tape numbers:
FLG001 through FLG010 (ten tapes)
This data set only covers about 35% of the planet surface in a somewhat
patchwork quilt-like fashion (although it does cover most of the more
interesting geologic areas). DIM data is 8 bits/pixel unsigned ints
(i.e., grayscale). The DIM data was derived via mosaicing and
resampling of Viking Orbiter digital images by USGS, Flagstaff. This
data has higher resolution spatial sampling -- 1/256 degree/pixel or
about 231 meters/pixel. There are four files on each of these tapes
except for FLG010 which has two. Each file is about 23 MBytes and the
whole data set totals about 872 MBytes.
It is possible that revised versions of these data sets may now be
available. We have had ours for almost a year. But, both data sets
are very new (i.e., as far as being processed by USGS and deposited in
NSSDC -- the raw Viking data is going on 14 years old), and USGS has
revised the DTM's once already and may do some more revision in the
future. (There are many errors due to the great amount of
approximation necessary since the data is very low resolution -- USGS
can apply more extensive processing to "clean up" various types of
errors.)
NASA Master (Online) Directory
------------------------------
For further information, you may want to check out NASA's online data
archive directory system. It is called the NASA Master Directory (aka
NODIS -- NSSDC'S ONLINE DATA & INFORMATION SERVICE) and is accessible
to the public via computer connection through Internet using 'telnet'
services.
% telnet 128.183.10.4 -- use login name NSSDC (no password needed)
This gives you access to the online directory info about all the NSSDC
data sets (currently about 1 TeraByte of data). It has help files and
prompting to get you started, though my opinion is that it's pretty
difficult to use unless you already know what you're looking for. But,
it is an interesting system to check out. This only shows you a
directory of data sets, though it is possible to place orders for some
data sets and documentation online. NASA is in the process of making
it possible to directly obtain some data sets online via ftp or similar
services.
Useful NSSDC Printed Material
-----------------------------
A very helpful printed document is "The National Space Science Data
Center", NSSDC 88-26, which may be order directly from NSSDC at the
above address (or possibly other fed. govt. printing offices). I
highly recommend this document if you are interested in NASA's space
data archives. It also includes information about research and
development NASA Goddard is doing in the areas of database organization
and accessing. There is an NSSDC Newsletter, which is a bi-monthly (I
think) printed report about recent news at NSSDC. You can get on the
mailing list for the NSSDC Newsletter by contacting Karen W. Satin at
NSSDC (see address above) or send email to her at
satin@nssdc.gsfc.nasa.gov. You can also request printed catalogs from
NSSDC that list all of their data sets (I've recently loaned mine out
and cannot tell their exact name or how to order them -- see the NSSDC
88-26 document).
Future NASA Planetary Data
--------------------------
There will be LOTS more! The current Magellan Venus mission and the
1992 to 1995 Mars Observer mission will return amounts of digital
terrain data that will dwarf what is currently available from NSSDC.
Also, the accuracy and resolution of these data will be much higher.
Digital elevation will be measured directly rather than computed from
visual imagery as in Viking (Mars Observer will have a laser
altimeter). Also, as parts of the Earth Observing System (EOS) of
NASA's Mission to Planet Earth (MPE) become operational, much more
Earth data will become widely available from NASA. If EOS ever becomes
fully funded and implemented (not likely due to federal budget
situation), it would collect a TeraByte a day of data!!! (Remember,
above I stated that NSSDC currently archives about 1 TeraByte which
represents all the planetary data NASA has ever collected.) If you have
interest in such terrain data, start now to learn about NASA data
systems and access to them through NSSDC.
Mars DTM Data Samplers Available from NASA Ames
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You may use anonymous ftp to stardent.arc.nasa.gov (128.102.21.44). cd
to directory 'pub'. Get the README file, and then any of the DTM data
set files, Val.west.*.Z. These are all DTM files of the western region
of Valles Marineris (Mariner Valley). Each differs by the amount of
sub-sampling done to the original file that we extracted from the
NSSDC complete planet data file. No filtering has been done to smooth
the data prior to sub-sampling (i.e., nearest neighbor sampling was
done), but the un-subsampled data is there for you to do so if you
wish. Each file has a 256 byte header (not textual), which is
described in the VPEheader.{man,cat} files in the ftp directory. DTM
files have been compressed via Unix's 'compress' (LZW encoding)
command. Remember to use 'binary' mode in ftp when getting the data
files.
Please refrain from requests for help with processing and displaying the
data on your system. We are very short staffed and provide this data
to you out of the kindness of our hearts.
Lew (Lewis E.) Hitchner, PhD
Visualization for Planetary Exploration project
Aerospace Human Factors Division
NASA Ames Research Center
U.S. Snail
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RIACS
Mail Stop 262-2
NASA Ames Research Center
Moffett Field, CA 94035-1000
email (Internet)
----------------
hitchner@riacs.eduhitchner@riacs.edu (Lewis Hitchner) (01/30/91)
The subscription address for the NSSDC Newsletter has changed. It is now:
Coordinated Request and User Support Office
National Space Science Data Center
Code 933
NASA Goddard Space Flight Center
Greenbelt, MD 20771
301-286-6695 (FTS 888-6695)
email: request@ncf.span.nasa.gov
NCF::REQUEST via the Govt's SPAN network