Creating TINs in ArcGIS from triangular elements?

When features are added to a TIN, there needs to be some way to define where their heights come from. If you are inputting 3D features, you can specify the Shape field as the height source. This indicates the z-values will be taken directly from the feature geometry. When adding 2D features, you can reference a numeric field. You can also specify None, in which case the features will first have their heights interpolated from the TIN before being added to it. This requires that some features be added to the TIN without the None option, so there will be some heights available to interpolate from.

Delineate TIN Data Area (3D Analyst) http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Delineate_TIN_Data_Area/00q900000087000000/

Method (optional) The method used when processing triangles. PERIMETER_ONLY will iterate through triangles from the TIN's outer extent inward and will stop when the current iteration of boundary triangle edges don't exceed the Maximum Edge Length. ALL will classify the entire collection of TIN triangles by edge length. The default is PERIMETER_ONLY.

The only way we found to get a triangular mesh with existing topology into ArcGIS was to use the arcpy.LandXMLToTin_3d function. It's a bit crazy to have to write out a LandXML file just to get your TIN into Arc, but it works. Here is a Python Toolbox for ArcGIS10.1 that accesses data on a triangular mesh from an ocean model, and brings it into ArcGIS as a TIN. https://github.com/rsignell-usgs/dap2arc/blob/master/dap2tin.pyt We've let ESRI know that a great enhancement would be to be able to instantiate a TIN directly using arcpy.