Chapter 16. Legacy Polygon and Polyface Meshes

The first surface entities implemented in AutoCAD (Release 10, 1989) were the PolygonMesh and the PolyfaceMesh. The PolygonMesh object consists in a rectangular grid of flat faces that approximates a 3D surface. The mesh density (number of faces) is defined from an array of M x N vertices. Each mesh face always has four vertices. The faces are arranged in a grid of M rows by N columns.
The PolyfaceMesh is very similar. It is created by specifying the coordinates for all of its vertices and once these are defined, the vertices that delimit each face are identified. In this case, each face of the mesh may have a different number of vertices and consequently the grid distribution characteristic of the PolygonMesh is not present. Visual LISP allows the creation of these surfaces using the command/vl-cmdf interface, entmake or the ActiveX extensions.
They are defined as a kind of POLYLINE entity. And as all variations of this type of entity they are very inefficient in terms of the storage space required. Right now these meshes are considered legacy objects, supported only for backward compatibility. To create 3D objects whose form is approximated by planar facets the much more versatile Subdivision Meshes should be used. This kind of mesh will be studied in Chapter 19.

This Chapter includes the following sections:

16.1. Mesh building procedures.
16.2. PolygonMesh.
16.3. Smoothing the PolygonMesh.
16.4. Sample Program: Creating a PolygonMesh.
16.5. PolyfaceMesh.
16.6. Sample Program: Creating a PolyfaceMesh.
16.7. Modifying Polygon and Polyface Meshes.
16.8. Summary.
Your questions or comments about this Chapter's contents are welcome!

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