
CSG Operations In modelling packages, basic geometric objects such as the cube or 'box', sphere or ellipse, torus, and a number of other shapes that can be described using a mathematical formula, are commonly known as primitives. These objects can typically be described by a procedure which accepts some number of parameters; for example, a sphere may be described by the coordinates of its center point, along with a radius value.
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 POVRay 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.
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