adding further shapes (as first assessment, with further extension based on use cases)

[lzehl]

#178 includes circle, ellipse, and rectangle

We should also add for mathematical shapes:
2D:
parallelogram
trapezoid
square
kite
rhombus
triangle

3D:
sphere
cuboid
cube
cylinder
cone
square pyramid

[Peyman-N]

I wanted to add Prism to this list.

[lzehl]

@Peyman-N @UlrikeS91 @xgui3783 @apdavison: If this is going to be part of v5.0 I would like to discuss this again a bit.

I fully agree with @xgui3783 that a rectangle and a square are parallelograms. Question here do we want to generalize the approach and join all quadrilateral shapes (square, rectangle, kite, parallelogram, rhombus, trapezoid) in one schema (quadrilateral) asking for 4 sides and the length of the two diagonals? Or taking this further group triangles, quadrilaterals, and all other polygons into one polygon schema (that can be adapted to the needed parameters; via e.g. embedded elements)? OR do we want to enable all (along the hierarchy of shapes)?

[apdavison]

do we want to join all quadrilateral shapes in one schema

In my opinion, definitely not. Named shapes have much more value as semantic elements:

1. easier data entry;
2. easier human interpretation;
3. easier to calculate attributes such as length of diagonals for a named shape than to infer the name of the shape from all the measurements (especially given floating-point limitations).

If a general schema for 2D shapes is needed (in addition to named shapes), then an array of vertex coordinates would probably be simplest (assuming straight edges). In this case, though, I would suggest taking a subset of the SVG specification, or some other existing spec. As for 3D shapes, I guess there's probably some standard from 3D modelling software.

[lzehl]

@Peyman-N which prism do you need since "prism" is to broad considering last comments from me and Andrew.