Terrain extractor interpolates their elevation by first finding the face that the point is on? How do you do Planar Interpolation?

I called Bentley and they told me that Openroads uses terrain extractor to interpolate elevations inside the triangles on a digital terrain model to create a surface, but I don't understand there method...
How can you gather large scale existing elevation information based off of an alignment?

Currently to get existing elevations based off of the alignment I use Civil Accudraw's Station-Offset feature along with the Analyze Between Points tool. However, I was hoping for a way to automate this...
Why manhole rim elevation assigned to pipe crown level?

Manhole rim elevation ref assign to proposed ground elevation. Still when seen in profile view manhole is not seen correctly.Refer Image below:
How can I set the Finished Floor Elevation of a building pad to a predetermined elevation?

Product(s): OpenSite Designer Version(s): 10.07.00.56+ Original Author: Marc Blancher, Bentley Technical Support Group Question: How can I set the finished floor elevation...
How to reduce number of triangles in terrain model on openroads?

Hey, How to reduce number of triangles in existing terrain model? I can not import point cloud again. Is there an option to filter triangles after the slope to merge triangles with similar slope?