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Is any way to produce cross-sections of a model?
G. G. Krupp
I would just make a shape that you can use with a Boolean operation to "cut away" part of the model. Say your model parts are grouped together in an object named "Model" and you can place a cube (rcc) in such a way that it will cut through your model. You could make a region called "cutaway.r" with the following command.
mged> r cutaway.r u Model - cube
Then just display the region "cutaway.r" when you want to view or ray trace a cross section.
mged> B cutaway.r
You can either use subtraction or intersection operations to get a cross section. The method ggkrupp mentions is certainly a common one.
Another common approach is to use the -k option to rt during ray-tracing. That will enable the use of a cutting plane defined by an xyz direction vector and a distance (defining a cutting plane).