What method does Terrain Extractor (Trex) use to interpolate elevations from a DTM / DEM / TIN / Contour?
For all data source types available in the Standalone, AutoCAD and MicroStation platforms, Terrain Extractor (Trex) currently interpolates elevations using the same highly advanced Digital Terrain Model (DTM) Technology as Bentley Civil products.
As of the CONNECT Edition release (10.00.00.XX) of the products listed in the header of this article, the Civil DTM first performs a conversion of the selected data source to a TIN (Triangulated Irregular Network). When processing a contour datasource, the Civil DTM does additional processing e.g. to make sure triangles do not cross contours, and do not end up on the same contour.
Once this is done, Trex looks at hydraulic model node (point) elements and interpolates their elevation by first finding the face that the point is on. It then does a planer interpolation to get the z coordinate value to populate the elevation. This is the current methodology used in the versions available as of this writing.
When using the ArcMap integrated version, several ESRI data source types are available in Trex. The interpolation method used for those data source types is controlled by ESRI/ArcGIS.
TRex Terrain Extractor Tool
Chapter ## of Algorithms, 4th Edition by Robert Sedgewick, Kevin Wayne (2011)