The Model Map shader generates surface tangency data for a polygon mesh, using a given texture projection. The tangent points in the principal U direction of the texture projection and the binormal in the principal V direction of the projection.
The shader can return either the surface normal at intersection, surface tangent or binormal. All of these vectors are orthogonal unit vectors and together compose a coordinate reference frame at the surface intersection called "tangent space".
The shader returns the vectors as encoded color information for ease in map generation. The red, green and blue channels encode the x, y and z vector components respectively. Each component value is range shifted from [-1,1] to [0,1].
In addition the shader can take as an input a previously generated normal map from, for example, a higher resolution object and transform that to the tangent space of the object this shader is applied to.
Selects the texture projection to use. See Specifying a Texture Projection [Texturing].
Specifies the vertex color property to use. See Specifying Parameter Maps or Vertex Colors in Property Editors [Scene Elements].