16.1.4.4 Annotating Metrics

A variation on the contouring idea, in [95], Teschner proposes a method for displaying metrics, such as 2D tick marks, on an object using a 2D texture map containing the metrics. Texture coordinates are generated as a distance from object coordinates to a reference plane. For the 2D case, two reference planes are used. An example application for this technique is to create a 2D texture marked off with tick marks every kilometer in both the s and t directions and map this texture on to terrain data using a GL_REPEAT texture coordinate wrap mode. An GL_OBJECT_LINEAR texture coordinate generation mode is used, with the reference planes at x = 0 and z = 0 and a scale factor set such that a vertex coordinate which is 1km from the x-y or z-y plane produces a texture coordinate value equal to the distance between two tick marks in texture coordinate space.