Extrusion is typically the first step to generate a 3D building from a 2D footprint. This operation increases the dimension; for instance, a two-dimensional building footprint can be extruded to a three-dimensional mass model. See extrude operation in CGA reference.


See the following examples for more information about extrusion:

Lot --> Lot.

A 2D building footprint in its initial scope (yellow). The scaled x- and z-axes of the scope are illustrated in red and blue, respectively. The y-dimension of the scope is zero.

2D building footprint in its initial scope
Lot --> extrude(4)

The 2D building footprint is extruded to a 3D mass model. The extrusion direction is orthogonal to the shape (along the normal of the footprint polygon). The scope has changed. In this example, the x- and z-dimensions are the same but the y-dimension of the scope has changed to the extrusion height.

If a footprint lies on a hill, it may be preferable to extrude along a world coordinate axis rather than the polygon normal. This and other extrusion variants are explained in the extrude operation topic.

2D building footprint extruded to a 3D mass model

In this topic
  1. Example