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From: shirley@uiucdcsm.UUCP
Newsgroups: comp.graphics
Subject: Re: Bounding extent questions
Message-ID: <4400003@uiucdcsm>
Date: Wed, 11-Mar-87 12:57:00 EST
Article-I.D.: uiucdcsm.4400003
Posted: Wed Mar 11 12:57:00 1987
Date-Received: Fri, 13-Mar-87 21:18:09 EST
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Nf-From: uiucdcsm.cs.uiuc.edu!shirley    Mar 11 11:57:00 1987




Semi-answer to 3):

    If the bounding sphere is to be used as an extent for the unit
primitive, a bounding ellipsoid can be substituted.  This ellipsoid
will correspond to the bounding sphere in primitive space.  This will
give you a tighter fit, but the ray will have to be transformed into
primative space.  If the extent is hit, the ray will NOT have to be
transformed again (the primitive space is the same for the unit prim
and the bounding sphere).  


A question about CSG ray tracing:

     How do you handle the interface between two transparent objects,
such as water and glass?  If they touch the basic union operation will
ignore the interface.  If they don't touch the water-air-glass will
have a higher reflection than is desired, so simply separating the objects
slightly doesn't cut it.  I currently treat very small separations as
a special case and ignore the air in the calculation the reflectance and
the refracted ray, but this is terribly inelegant (as well as making
object specification ugly).  Is there a nice way to handle this?

Thanks

Peter Shirley
U of Illinois at U/C