The URL quoted by willf is the only one I've seen that provides a tutorial about converting parametric equations to Carrara/RD format. Other sites with parametric equations that can be adapted to Carrara/RD: http://www.swin.edu.au/astronomy/pbourke/geometry/ http://mathworld.wolfram.com/topics/MiscellaneousSurfaces.html http://www.uib.no/People/nfytn/mathgal.htm SMcQ