Thank you for the very detailed answer! I know there are some methods to get the data from triangles, but my purpose is to change the triangles (specifically, delete some of them) inside the TGraph2D or TGraphDelaunay2D object. Can you give some suggestion how can I do it? Like shifting the address of Object pointer of TGraph2D?
The purpose is relating to this question, I want to delete triangles that out of concave curve.