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From: sugtech@lll-lcc.UUCP (SUG Tech Committee)
Newsgroups: net.graphics
Subject: Ray tracing questions
Message-ID: <386@lll-lcc.UUCP>
Date: Wed, 20-Aug-86 00:19:05 EDT
Article-I.D.: lll-lcc.386
Posted: Wed Aug 20 00:19:05 1986
Date-Received: Wed, 20-Aug-86 23:09:30 EDT
Distribution: na
Lines: 46
Keywords: ray tracing


I have some questions concerning ray tracing and I would appreciate
anybody's help.

1.)  What do you do when a ray intersects a polygon straightway (the
     ray lies in the plane of the polygon)?  One could have a scene in
     which several polygons resided in the same plane, each one behind
     the other.  One would have to determine the closest one, in order to
     dsisplay the proper color.

2.)  What is a fast method of finding the intersection of two 3D lines?
     Determinant?

3.)  Are there any new ways of antialiasing other than super sampling or
     stochastic sampling?

4.)  Is the Cook-Torrance shading model the most accurate one to date or
     is there a better one?

5.)  What is the advantage of applying modelling transformations to rays
     and not to the objects (see Roth's paper, 1982)?  It appears that this 
     would slow down the ray tracing process, since the transformations need
     to be applied within the double for loop.  A detailed explanation
     and an example would really help here.

6.)  What should one do to calculate the depth of a polygon at a certain
     point if the plane equation coefficent "C" is equal to zero?
     Examples would be N = (0, -1, 0, 1) or N = (1, 0, 0, -1).  The 
     forumula  z = (-d -ax - by)/c does not work in this case.

7.)  What are some of the visual effects that ray tracing cannot yet model?

8.)  I read in the book "Procedural Elements for Computer Graphics",
     p. 379, that small objects may be lost if they are viewed indirectly by a
     curved surface.  Is there any way to prevent this?

9.)  Are there text books out now that have lengthly, detailed sections on
     ray tracing?

10.) This question is concerned with the method of antialiasing used by
     Whitted.  Michael Sweeney, in his master thesis, stated "that the four
     corners of a pixel are considered to be the same color if the sum
     of the differences in their red, green and blue components is less
     than this threshold (the threshold being a value specified by the
     user)".  Could someone please show me how the sum referred to by Sweeney
     is derived, given his explanation?