Duffer is a .Net library for writing IDTF files which can be fed into IDTFConverter to create U3d files
http://sourceforge.net/projects/u3d/ The oringal reference C++ code for creating U3d files
http://www2.iaas.msu.ru/tmp/u3d/ Based on the original sample, updated to CMake and other fixes
http://jmol.svn.sourceforge.net/viewvc/jmol/trunk/Jmol/src/org/jmol/export/_IdtfExporter.java?revision=HEAD&view=markup A useful reference for other IDTF writer implementations