Volume rendering prob

[Elizabeth Bullitt]

Could anyone provide insight into the following problem?

I would like to combine perspective surface rendering of various objects
with perspective volume rendering of other objects. The input data for
the volume rendering is a structured point dataset with associated
scalar color data, and with axially unequal, floating point spacings of
[xstep, ystep, zstep]. 
	All objects, whether surface or volume rendered, are positioned within
a global coordinate system via SetUserMatrix(). 

	I have had not had any problem with surface rendered objects. The
problem is with selective volume rendering within the same global
coordinate space.

	I can get the CONFINES of a requested volume rendered region to display
correctly under various rotations/translations relative to surface
rendered data, using SetSpacing(xstep, ystep, zstep) to help define the
structured points volume. The CONTENTS of the supposedly volume-rendered
volume is, however, bad and often blank.
	Under a test program, I can get the contents of an individual
volume-rendered region to display correctly both initially and under
various rotations/translations only if I finally rescale the final
volume by (1/xstep, 1/ystep, 1/zstep). This makes the contents correct,
but the CONFINES of the the volume rendered region incorrect relative to
other objects within a world coordinate system.

	Suggestions would be genuinely appreciated.
Liz


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