Can I get face's UV mapping transformation matrix from C API

[DanRathbun]

Neither the C API nor Ruby API have a method or function to get this transform.

You’ll have to construct it yourself. See this other topic in the Ruby API category …

Texture Transformation matrix

If you can get the [U, V] from [X, Y, Z] you can query enough information to reconstruct the matrix and its inverse. I have an old code sample for the full matrix (that includes perspectivic distortion), but it is very slow in Ruby. Maybe it is faster when reimplemented as C extension. SketchUp’s API should have something like UVHelper.get_XYZ(uvq)