Complete rework of parts and further questions

[Manfred Schaefer]

4 is a concave quad is is not allowed per the file format spec. 

From the spec:

Hello Orion,

Thank you.
I had only thought of lenses when I heard the term “concave” and didn't see any connection to quadrilaterals.
I found a good description on the Internet and now know when a quadrilateral is concave, namely when both diagonals lie within the quadrilateral.

Best regards

Manfred