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page 124

Primitives may come from,

-Traditional Sources - Blocks, Spheres, Wedges, etc.

-Surfaces - A Volume is assigned to a surface model

-Previous operations

-others ?

CSG editing requires storage of the results of operations. This is because a part may be used many times to cut another part, for example a chamfered hole for a sunken screw.

The fundamental CSG operations are,

Union - both parts joined as one Intersection - Only where two parts overlap

Subtraction - only where parts do not overlap, One of the parts is typically discarded.

Subtraction case A (cuts hole in block)

two primitives before the operation

Subtraction case B (cuts off end of cylinder)

Union (both shapes merged into one)

Intersection (bottom of cylinder remains)

DI:15.5 USER INTERPRETATION OF THE GEOMETRIC MODEL