. What do you understand by DTM? How is generated?

Question

about photogrammetry

Answer 1

I assume by DTM you are talking about a Digital Terrain Model.  I'm not as sure about the photogrammetry way of creatingthem but I know the basics of how to create one utilizing drafting programs and survey information.  Typically they are the result of creating a Triangular Irregular Network or TIN.  

First you get 3d information in the way of survey data or contour information and plot your points in three dimensions with X,Y, and Z coordinates.  Then you can have the computer program connect the 3d points and make them into 3d triangle shapes which are all interconnected.  These triangular shapes which are created are actually flat planes which connect the known elevations and interpolate all of the elevations in between.  Obviously the more points you have, and the closer together they are the better the resulting model will be.  These flat planes of interconnected 3d points make up the triangles which compose the digital terrain model.