Advanced Graphics Study Guide

Part 4: Other 3D modelling mechanisms
A: Generative models
B: Converting swept objects to polygons
C: Constructive Solid Geometry
D: Implicit surfaces, voxels and marching cubes
E: Subdivision surfaces
...back to part 3 | on to part 5...

4B) Converting swept objects to polygons

Swept objects are hard to ray trace. Imagine trying to write a ray/object intersection algorithm for a general swept object. This means that we generally need to polygonise swept objects in order to render them. For PSC we obviously must convert them to polygons.

A swept surface may be easily converted to polygons by converting the outline of the 2D cross section to a polygon, and converting the sweep path to connected set of line segments. Moving the polygon to each vertex of the set of line segments, and connecting vertices accordingly, will produced a polygon mesh which approximates the swept surface.

Exercises [1998/7/12] Show how to convert the swept object from Part 4A Exercise 1 into polygons. What extra work would you need to do if you had to convert it into triangles?

Part 4: Other 3D modelling mechanisms
A: Generative models
B: Converting swept objects to polygons
C: Constructive Solid Geometry
D: Implicit surfaces, voxels and marching cubes
E: Subdivision surfaces
...back to part 3 | on to part 5...