[fsloth]

See for example Ian Stroud ”Boundary Representation Modelling Techniques” for a light introduction. The OpenCascade project is a fairly complete example of a complete one. But there is no ”by the book” way to do it - it requires both design and engineering savvy.

The simple explanation is the capability to model 3D shapes in a way that you can output the data to the rest of the manufacturing process. Hence what manifacturing process you target at least partially dictates your constraints.

The output could be - engineering drawings, CNC machines, 3D printers. Or another 3D modeling application down the pipeline.

In a way ”CAD kernel” alone is a worthless as a spec since it’s too general, just like ”a vehicle” is a useless spec for engineering.

CAD kernel- for modeling what, by whom, and where.

Naturally questions of numerical robustness and exactness of presentation soon enter the picture. How large or precise features do you need to model, for example.