Heightmaps are a greyscale image of the texture being used. Heightmaps will give the perception of depth to a flat image or texture by creating a shadow effect on the texture.
A heightmap will be used if Enable Relief Depth has been selected under Options-Face Options for the selected 3D mode.
Once enabled, editing the texture and changing the Relief Depth will show the effect.
****** If a texture does not have a heightmap associated with it,
SoftPlan will create one automatically for the texture.******
To best see the effect of a heightmap, generate a Textured 3d on a brick wall. Use the Edit Surface command and click on the surface of the brick. Double click on the texture and in the top right, select Use Color, make sure Relief Depth is set at about 50 and Enable Relief Depth is selected. You should see the effects that the height map has on a simple solid color. The relief depth effect is dependent on the lighting on the model and will not show as well if the ambient light is set too high.