          OPERATING INSTRUCTIONS FOR 3-DEM RAYTRACE SOFTWARE

CONCEPT OF OPERATION

   3-DEM will produce ray traced landscape scenes from USGS Digital
Elevation Model (DEM) files and from NASA Mars Digital Topographic Map (DTM)
files.  3-DEM scenes are true three dimensional projections which require
the use of red-blue 3D glasses for viewing.  Completed scenes may be saved
as Windows bitmaps for transfer to other applications.

SOURCES OF DATA

   DEM files are available via ftp for most of the United States and many
other areas of the globe.  Spectrum.xerox.com has a good selection of high
resolution 7.5' DEM files.  The USGS offers a large selection of 1 degree
DEM files for ftp from edcftp.cr.usgs.gov.  Many other locations can be
found on the Internet.

   DTM files for Martian landscapes are available on NASA CDROM.  Volume 7
of the 14 Volume Mars Digital Image Map collection contains the Digital
Topographic Map of the entire surface of Mars. This CDROM is available for
a modest price from the National Space Science Center.  Contact
request@nssdca.gsfc.nasa.gov to request a copy of the NSSDC CDROM catalog.

EQUIPMENT REQUIRED

   3-DEM is designed to run under Windows 3.1 with 256 color graphics.  A
486 or better microprocessor and math co processor are recommended.  You
won't be happy with the program's speed if you use anything less than this. 
At least 8 MBytes of memory is REQUIRED.  And if you can afford 16 MBytes,
it will significantly improve performance on large DEM files.

SEQUENCE OF OPERATIONS

   To produce a three dimensional scene you must perform four operations in
sequence with the 3-DEM software as follows:

   STEP 1 - Load a new DEM or DTM file and draw an overhead map of scaled
altitude data.  Choose "New DEM" or "New DTM" from the "File" menu and
select the file to be loaded into 3-DEM.  If the file is of the correct
type, 3-DEM will then draw an overhead map of the entire geographical area
with color scaled to the altitude at each point on the map.

   STEP 2 - Choose an area from the overhead map for conversion into a
three dimensional scene. Click the left mouse button at the location on the
overhead map which interests you.  The area to be converted will be outlined
by a black rectangle.  The observer's location and direction of view are
indicated by a notch in one side of the outline rectangle.  Move the outline
rectangle while holding down the left mouse button.  Rotate the outline
rectangle while holding down the right mouse button and moving the mouse
left or right at the bottom of the display window.  You can also make fine
adjustments to the rotation of the outline rectangle using the left and
right arrow keys.  Choose "Show Scale" from the "Scale" menu to display an
indication of the horizontal and vertical scale (in kilometers) of the
selected area.

   STEP 3 - Compute and display a three dimensional wireframe preview of
the area selected from the overhead map.  Choose "Wireframe Preview" from
the "Operation" menu and a dialog box will appear giving you selection of
the detailed parameters required for the three dimensional projection.  Each
of these selections is described in the following paragraph entitled
"Projection Parameters."  Initially however, you should accept the default
values by clicking the "OK" button.  3-DEM will then draw a three
dimensional wireframe preview for viewing using red-blue lens glasses.  If
you are not satisfied with the view, go may back to the "Overhead Map" and
adjust the outline rectangle position or rotation.  Or you may adjust any of
the projection parameters by choosing "Wireframe Preview" again from the
Operation Menu. 

   STEP 4 - Once you are satisfied with the wireframe preview, compute and
display a three dimensional ray-traced image of the selected geographical
area.  Choose "3D Ray Trace" from the Operation menu and 3-DEM will then
compute separate left and right eye ray-traced images and combine them into
a single scene for viewing with red-blue lens glasses.  Depending on the
size of the scene and the speed of your computer, this operation can take
from 10 minutes to an hour. Relax and be patient.  Once the ray-tracing is
complete, you may save the image as a windows bitmap by choosing "Save BMP"
from the File menu.

PROJECTION PARAMETERS

   Before 3-DEM computes a wireframe preview, you will be presented with a
dialog box for selection of detailed display parameters.  Each of these
parameters is described here.

   LEGEND - The Legend is text which will appear at the top of your
finished three dimensional scene.  Initially, this legend is read from the
DEM file header.  Adjust the text to your own preference.

   SCENE TILT - The scene can be tilted to the observer's line of sight by
a value of 0 to 45 degrees.  A tilt of 0 indicates that the observer's line
of sight is parallel to the base of the scene.  The default value of 26
degrees usually gives a suitable result for a foreground projection.  Use a
smaller value (12 to 16 degrees) for a background projection.  See the
description of foreground and background projections which follows. 

   VERT MAGNIFICATION - Large scale DEMs and DTMs often show very low
relief features.  Vertical magnification increases the height of surface
features to make them more visible in the three dimensional projection. 
Don't hesitate to use magnifications of 200% to 300% or more to improve the
appearance of your scene.  The default value of vertical magnification is
100%, but you should change this value if you are not satisfied with the
appearance of the wireframe preview.

   VERT SHIFT - Occasionally, you may wish to shift the vertical position
of your projection on the screen to obtain the best scene.  Enter the number
of screen lines to be shifted, where positive values shift the image toward
the top of the window, and negative values shift the image toward the
bottom.  Normally you will not need to change vertical shift from a value of
zero.  However, this control gives you the flexibility to do so if needed.

   ILLUMINATION - The three dimensional ray tracing is computed using one
source of illumination at the azimuth and elevation angles chosen here. 
These directions are relative to the observer at all times.  Zero degrees
azimuth indicates a source directly in front of the observer, while 180
degrees azimuth indicates a source directly behind the observer.  Zero
degrees elevation indicates a source on the horizon, while 90 degrees
elevation indicates a source directly overhead.  Thus the default values of
240 degrees azimuth and 60 degrees elevation indicate an illumination source
over the left shoulder of the observer.  Experiment with these values if you
find a need to change the appearance of light and shadow in your three
dimensional projection.

   TERRAIN - Normally, terrain is a combination of mountains and plains
with lighting determined by the azimuth and elevation of the illumination
source. However, if you are developing a scene containing the ocean's
surface, you may want the ocean to appear uniformly dark rather than appear
as a brightly lighted plane.  Choose "Mountain and Plain" for normal
scenery, or "Island and Ocean" for scenery including the ocean's surface.

   LENS SELECTION - There is no standard arrangement for the red and blue
lens of 3D glasses.  Some glasses have the red lens on the right, some on
the left.  Choose "Red/Blue" for red over the left eye or "Blue/Red" for red
over the right eye.

   PROJECTION - "Foreground" and "Background" options are provided for the
three dimensional projection.  A foreground projection is centered at the
surface of your CRT screen and projects into the space in front of the
screen, giving an image that you can literally reach out and touch.  A
background projection is a more conventional projection behind the surface
of your CRT screen and is more suitable for large scale scenery views. 
Experiment with these options in the wireframe preview before computing the
ray-traced image.

OTHER CONSIDERATIONS

   LOADING DEMs - Full sized one degree DEMs are enormous ASCII files of up
to 10 MBytes size which must be translated byte by byte into the binary
values usable by the software.  Don't be alarmed at the time it might take
to translate a full sized DEM and compute an overhead map.  The smaller 7.5'
DEMs load much more quickly and require much less memory.  It is recommended
that you use only 7.5' DEMs if memory is short.

   LOADING DTMs - DTM files on the NASA CDROM are named as "tg00n000.img"
or "tg00s000.img" where "00n" or "00s" are degrees latitude (north or south)
and "000" is degrees west longitude. The CDROM also contains digital
photographic images of the surface of Mars named as "mg00n000.img" or
"mg00s000.img."  Don't confuse these photo files with the digital
topographic map files.  DTM files are binary files (unlike the ASCII DEMs)
and are easily digested by the 3-DEM software.

   SPEED - Everyone wants more speed.  But please take into account that
3-DEM is actually computing two separate ray-traced images, one for the left
eye and one for the right eye.  To improve speed, keep your image window to
a reasonable size and rely on the smaller foreground projections.  A 1024 by
768 background projection will take a LONG TIME to compute.  If you want to
try something like this, I suggest that you allow 3-DEM to run in the
background while you do other things.

   MEMORY - More is better.  3-DEM manipulates large amounts of data in
memory.  Using virtual memory for these processes is workable, but slow. 
And you may be alarmed by the gyrations of your disk drive.  If you have 16
MBytes of memory, 3-DEM will never need virtual memory - even for one degree
DEMs.

REPORTING BUGS - Please report any bugs or send any questions to
rshorne@delphi.com.  I'm also interested in any comments or suggestions for
improvement of 3-DEM.

						Richard Horne