You may find information on this in: "Automatic SketchUp - Creating 3-D Models in Ruby" by Mathew Scarpino Permissions may be sought directly from Eclipse Engineering LLC: Fax: (925) 262-1757 E-mail: info@eclipseengineer.com Appendix B: Advanced Geometry..................................... 391 B.3 Introduction to Transformation Matrices .........................................406 B.4 Combinations of Transformations...................................................415 B.5 Transforming Points and Vectors....................................................418 B.6 Mathematics of Combining Transformations....................................423 You may find helpful links here: http://sketchucation.com/forums/viewtopic.php?f=180&t=10142&p=573943&hilit=automatic+sketchup#p269709