16.1.4.3 Contouring

Contouring is closely related to height fields. If the data values are organized into regions, the relationship can be represented as a 3D contour map. Each data value divides up the terrain into regions, bounded by isolines. Each region is displaced a different height above the reference surface. The boundaries of each data value can be stitched together and tessellated, producing a 3D surface. Alternatively, the region can be sampled, and rendered as a height field. In both this and the previous technique, the elevation data can be delineated with color values on the surface, as with topological maps. This can be easily rendered with a one-dimensional texture and the use of the texture generation functionality in OpenGL:

1.

Create a 1D texture map with the desired color values.

2.

Configure texgen to map different elevation values to texture coordinates (e.g. map y values to s coordinate values).

3.

Render the surface with 1D texturing and texgen enabled.

You probably want to use GL_EYE_LINEAR texture generation, so the surface can be manipulated relative to the viewer without changing the texture mapping.