I have such an attached 3D surface and a polygon on it. (Code is provided below)
I aim to crop the portion which is only inside the polygon and delete everything outside the polygon.
I found out the function of "inpolygon", but it did not work well enough since it is for 2D.
Then I encountered with "inpolyhedron" which is written for 3D, but was not that successfull on using it.
Is there any other way that you would suggest?