Michael Boccara (boccara++at++MIT.EDU)
Thu, 27 Aug 1998 11:33:50 -0700
The basic methode for coping with double precision, and moreover for a space
application, is to put the origin of the pfScene as close as possible to the
camera.
My method was to know in double position the absolute position of the various
spacecrafts from the Earth Coordinate System (origin at center of earth), and
the cam's postion in float precision related to one of those spacecrafts.
When your camera is positionned in outer space, and the scene origin on one
neighboor spacecraft, the large coordinates are reported to the earth's position
and the far away other spacecrafts. The earth will be big enough to handle the
loss of precision without jittering, and the other spacecraft are too far to be
seen !
To give you some kind of mathematical formula, the needed precision for
visualizing a 3D object is :
precision_needed = object_size / object_distance_from_origin
Also, when you will deal with drawing both spacecrafts and the earth, be careful
with the limitation of the Z-buffer precision :
You need to visualize close objects, so to put the near to 1 meter or so, and
also to see at least the earth, so to put the far to at least 20000km. This is
overwhelming for the supported Z-buffer precision if you want to avoid the
scattering of the earth's polygons.
The best slution is to use 2 superimposed channels, with complementary near/far.
Hope this helps,
Mike
--
___________________________________________________________________
Michael Boccara Massachusetts Institute of Technology
Research Laboratory of Electronics
(617) 253 0005 Virtual Environment Technologies for Training
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