@xgui3783 and @apdavison before I continue here I would need your feedback.
Goal of these schemas are to define mathematical shapes without defining an actual coordinate space.

Which one do we most likely need ? How do we define them best / consistently ?

My immediate focus is that (IMO) all are 2D shapes, except sphere, which IMO is a 3D concept. Its 2D concept would be a circle.

I can Imagine circle used.

Would line segment also be included (or is it already included in a previous commit?)

Seems strange to not have rectangle, though one would argue that a rectangle is a special parallelogram. But the same can be said for square.

@xgui3783 #186 has various 3D shapes besides sphere. But before I implement them I wanted to have feedback.

I would define a line as a coordinate point only within a given space. Therefore it is excluded here from mathematical shapes that are defined without a space. There will be another PR in connection with the annotation revision with a Contour schema (which can be a line).

Note that circle, rectangle and ellipse were already added to mathematical shapes in a previous PR.