[digdugdirk]

While similar at a glance, the underlying functionality between a 3d modeler and a CAD kernel is tragically completely different.

Even FreeCAD has some fundamental differences (and lack of functionality) between it and other mainline CAD programs.

Hopefully someone with more knowledge and experience than me can hop in and explain more, I'm just a CAD user, not a CAD kernel developer.

[bschwindHN]

I'm not an expert either, but it could be compared to bitmap graphics vs. vector graphics.

3D modelers like blender (or even OpenSCAD) work with a bunch of triangles - there is often not some higher level representation of the geometry. You could put a drill hole in a part, but it ends up as just a ton of triangles that approximate that drill hole, vs. a file format which semantically encodes "there is a cylindrical drill hole at this location, with this vector direction, and this radius".

That's what things like BRep (Boundary Representation) and STEP files give you is that semantic data which describes the part "here are the edges, faces, dimensions, etc.", vs. "here's a bunch of triangles, good luck machining this"

[throwgfgfd25]

> but it could be compared to bitmap graphics vs. vector graphics.

This is very much how I internally understand it and explain it to people, yes!

It is a good analogy for e.g. why it's often a challenge to get something milled with a CNC when you only have an STL file.

STL is like a PNG line drawing: it can be high quality, but it's not describing the drawing. STEP is like SVG: it's more effort to render it, but it contains the instructions to draw it.

[ortsa]

Isn't the problem with that analogy that there are things like NURBS which are pretty directly analogous to vectors (and isn't a surface a boundary?)

Edit: Along with the fact that blender has a lot of non destructive workflow steps (that usually get baked out into the "bitmap", to further your analogy)

[bschwindHN]

It's not a perfect analogy, and Blender does have some parts which resemble the sort of data structures you'd use in a CAD modeler.

I think with enough plugins and customizations, you _could_ twist blender into something that resembles a CAD modeler, but it's really an uphill fight compared to selecting tools which were designed with that goal in mind from the start.