Next: 16.1.4.4 Annotating Metrics
Up: 16.1.4 Rendering Data Values
Previous: 16.1.4.2 Height Fields
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.
Next: 16.1.4.4 Annotating Metrics
Up: 16.1.4 Rendering Data Values
Previous: 16.1.4.2 Height Fields
David Blythe
1999-08-06