Collection of Education/collectionofeducationcarat1997.iso/SCIENCE/3DEM.ZIP/README.TXT

Text File | 1995-10-21 | 11KB | 200 lines

       OPERATING INSTRUCTIONS FOR 3-DEM RAYTRACE SOFTWARE (Version 1.4)

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 can produce either standard shaded three dimensional
projections or red-blue 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
[e-mail] 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.
3-DEM also runs well under Windows 95.  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 "1x" or "4x" from the "Area" menu to select the size of
the scene.  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.  You can choose a preview projection
with or without the use of red-blue lens 3D glasses for viewing.  Choose
"Wireframe Preview" and either "Red/Blue" or "Single View" 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 the three dimensional
wireframe preview.  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.  Your ray traced image may be a red-blue projection requiring 3D
glasses or individual projections from center, left eye, or right eye
viewpoints. Choose "3D Ray Trace" and either "Red/Blue", "Single View,
Center", "Single View, Left", or "Single View, Right" from the "Operation"
menu and 3-DEM will then compute the selected ray-traced projection.
Depending on the size of the scene and the speed of your computer, this
operation can take from 3 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 pro