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EARTH.NOT
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1992-07-26
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ORTHOGRAPHIC EARTH
by Matthew Merrill and Dave Ransom
Version 9230, July 1992
-----------------------
The original code for ORTHOGRAPHIC EARTH was written by Matthew Merrill
to work out the details of the projection and test to the features for
use in his program SOLAR.
Version 9230 has been modified by Dave Ransom, RPV ASTRONOMY BBS, to improve
the performance, to include EGA compatibility for use on systems so equipped,
and to allow for motion. Note that the EGA mode on some VGA-equipped systems
does NOT always perform correctly.
EARTH is a VGA/EGA demonstration of the orthographic projection method of
displaying the Earth. The program is NOT compatible with other display
types. The default values are set to display the full Earth centered
approximately on Los Angeles, California. The user may enter any desired
zoom factor from 10% to 500%, set the map center coordinates (latitude and
longitude), and select whether or not to display a map grid. The prompts
are self-explanatory; values enclosed in square brackets [...] are the
default values which will be used if ENTER is pressed.
The drawing time is a function of the speed of the computer and whether or
not it has a math coprocessor chip. A math coprocessor is NOW relatively
inexpensive and is STRONGLY RECOMMENDED! For example, the time using the
default values is approximately 5 seconds on a 486DX and approximately 30
seconds on a 286/287. Times for computers without math coprocessor chips will
be MUCH longer, on the order of several minutes even for 386 systems!
The following command line options may be included:
/EGA Force a VGA monitor to use the EGA mode.
/ROT Display the Earth in motion, five degrees rotation per
display. This option is ONLY available in EGA resolution
and forces EGA mode on VGA monitors.
/MON Force monochrome operation.
If automatic rotation is enabled with the "/ROT" command line option AND the
zoom factor is less than 100%, the zoom factor will be increased by 5% for
each drawing cycle until it reaches 100%. For a demonstration of the rotation
and zoom features, enter
"EARTH /ROT"
at the DOS prompt. Then enter "N" to provide manual parameters, enter "10" for
the zoom factor, and press ENTER for the remaining prompts. Press ESC to stop
the automatic rotation and press ESC again to quit the program.