Constructive Solid Geometry

Constructive Solid Geometry, or CSG, is a modelling technique used in 3D computer graphics, in which complex shapes are formed through the boolean union, difference, or intersection of basic geometric shapes.

CSG Operations

In modelling packages, basic geometric objects such as the cube or 'box', sphere or ellipse, tetrahedron, torus, and a number of other shapes that can be described using a mathematical formula, are commonly known as primitives.

Boolean Union

A boolean union of two primitives is analogous to 'merging' them together, and treating them as a single object. This graphic depicts a boolean union:

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.

Boolean Difference

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.

Boolean Intersection

A boolean intersection of two primitives is the creation of a new object that takes the shape of the area where the two primitives overlap. The next graphic shows this happening:

Here we can see that the area where the blue sphere and red cube overlap has been turned into a new shape.

In particular, the Unreal game engine uses this system.

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