Thank you GM, Since I am very new to Asymptote, there is a doubt in few keywords. I searched for the keyword "patch", but I couldn't able to find proper definition. I will take some time to understand the code that you have replied
I'm not a beginner in the use of Asymptote but I confess to have used it, almost exclusively, for the 2D geometry.
I hope, for many years, that Asymptote will be improved for 3D geometry (intersections, dashed hidden lines, resolution of the problem of insufficient memory, ...) but I suppose that they're not easy problems to solve for the authors of Asymptote.
It is courageous to study the crop3D.asy file but I admit to having used it without studying it: I discovered the existence of this file yesterday.