I'm now looking to create more general surfaces, but searches for the triangle/mesh/nurbs/facet in the help file returned no results. Is this possible?
All geometry creation methods are in ITxGeometryCreation interface.
There are some methods that are not working for Process Simulate and Process Designer – they throw TxNotImplementedException, so check the summary of the methods to make sure they will work for you. The ones that you are particularly looking for (triangle/mesh/nurbs/facet), we don’t have methods that create such geometry objects.
I am not familiar with your requirements, but we have also another object TxManipulator, that can also contain geometry elements (Placement Manipulator is of such kind). You can create plane elements under it and many others (see TxManipulatorElementData).