Draping GIS Features on Terrain

A common need is to display conventional 2D GIS features (points, lines, polygons) on a 3D terrain.  The process of projecting a 2D feature on a 3D surface is known as "draping".  For very simple features, or a very flat terrain, this is almost trivial, but for complex features on uneven terrain, it is difficult to draw the features perfectly.


Lines (Polylines)


Problems with Draping Geometry

  1. Z-buffer fighting.  If the feature (point, line, or polygon) is exactly on the terrain surface, it can conflict with the rendering of the terrain surface itself.
  2. LOD problems.  For terrain systems which use LOD (of any kind), a feature draped on one level of detail may intersect the terrain whenever the LOD changes.

The most common solution to these problems is to raise the feature geometry by some offset, such as a few meters.  This is usually visually acceptable if the viewpoint will remain must higher above the terrain than the offset.  If the camera is very low, the offset must be small so that the feature does not appear to "float" above the terrain.  If the camera is very high, the offset must be large for Z-buffer precision.  Some software (such as Google Earth) deals with this by using a dynamic offset, raising the feature geometry as the viewpoint elevation increases.

Texture Draping

Other Approaches

Related Issues