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The red cube and the blue sphere are combined using the CSG union operator to create a single object, with the appearance of both primitives merged together.
Some software distinguishes the Union from a different operator, Merge, which does the union in such a way that the surfaces inside the merged region are not rendered. This would be desirable in cases where the objects are transparent, and the union should be treated as a single solid object. In particular, the POV-Ray graphics package implements this concept.
A boolean difference of two primitives is like 'subtracting' one or more objects from another object. This graphic shows a boolean difference in action:
Here, we see that a portion of the blue sphere has been sliced away from the red cube.
A boolean intersection of two primitives is the creation of a new object that takes the shape of the area where two or more primitives overlap. The next graphic shows this happening:
Here we can see that the volume where the blue sphere and red cube overlap has been turned into a new shape.
Constructive Solid Geometry has a number of practical uses. It is used in cases where simple geometric objects are desired, or where mathematical accuracy is important. The Unreal game engine uses this system.
wikipedia.org dumped 2003-03-17 with terodump