What does an Interferogram represent? A 3D visualization

I found this great way to visualize an Interferogram so that with practice one can glance at an igram and "see" it in 3D.
To create these same visualizations or to alter them (e.g. just change the xtilt or z8 terms and re-run), paste the below code into left window of openSCAD (free and light weight open source software for PC,Mac,Linux), then hit F5 key and wait 3 to 10 seconds. Then you can drag the resulting model around with your mouse.
The code to copy into openSCAD is here: gr5.org/3digram...

[@guybrandenburg2954]

I would like to highly applaud this video and your efforts in making interferograms understandable. I found the visual explanation of a tilted mirror and countour lines extremely helpful. Congratulations, and thanks! I didn't at all like the fact that i-grams were such a black box -- as a retired math teacher myself, I felt somewhat suspicious that such an important measuring method simply had mathematics that was simply beyond my ken. Didn't feel right.