I don't understand this. You can make triangles small enough that you can't tell the difference, and define them mathematically in terms of curves..? Isn't this how any rendering will ultimately work? The primitive is triangles.
Yes, but the representation as arcs allows one to defer the conversion to polylines/triangles until a later time.
As an example, if doing V carving, the appearance will be smoother if the geometry is imported so as to have arcs/curves, deferring the conversion to polylines/straight line movements until the last possible moment on the machine.
Arcs/Curves are also easier to work with if one needs to edit, and are more efficient in terms of representation/disk space/storage.
Well, you could export enough triangles to get less than 0.0005" variance, but in practice actual CAM software will choke on it is my impression; I sent some circular objects out to be machined, but they just treated by OpenSCAD-exported files as a secondary reference for them redoing it in real software.
CAM people, for example drive numerically controlled machines and robots. (CNC machines) These machines are driven by lines, arcs, higher order analytic curves, such as the conic, and recent controllers will accept bsplines.
Having path planning done with real geometric entities brings a lot of benefits along for the ride! Accuracy without a bazillion entities for the look ahead system to manage and for program buffers to drip feed (DNC) to a machine that probably does not have a large enough program memory to deal with that bazillion entities.
In many cases, derivative or extrapolated curves do not convey the right shape or path or are difficult and time consuming to force conformance.
We ended up with the big geometry kernels, such as Parasolid, precisely so that CAD could create a brep (boundary representation model) of sufficient fidelity to make other tasks, such as CAM and simulation, as well as derivative designs possible, practical, repeatable.
Those big code bodies have so damn many man hours of development in them it is very hard to replace it all. And that means we are stuck with some things, like many operations being single threaded, which caps CAD design to be a function of sequential compute speeds.
There are ways to build models to eliminate some dependencies, and the same goes for assemblies, so that multi-processing of some sort is possible. That brings our multi-core CPUs into the game.
But those are hard to teach, a lot of software does not yet support multi-threading anywhere near enough to fully exploit the model work, and, and, and...
In the CAD / CAM world, the primitive is the b-spline, and the surfaces it can represent.
Those generate faces, trim boundaries and sets of those create boundary representation models.
And still those can cause grief. They might be open, or just a surface representation. Or, they may self intersect...
Basically, every edge, which boils down to a b-spline curve that matches up to another b-spline curve serving as a trim boundary of a surface, must be shared by two and only two surfaces or the model is not representative of a real world, manufacturable thing.
Another great observation regarding real world objects is there are no edges, just radii, if only a single molecule big. Just an interesting and perhaps useful aside.
And b-splines are constrained to conform to the properties of lower order entities, such as lines, arcs, and the like. This is a part of why wireframe entities are all called "curves" or "sketch curves." They literally are all b-splines constrained by number and or placement of control points.
>You can make triangles small enough that you can't tell the difference, and define them mathematically in terms of curves..?
This doesn't work if you already have a mesh. You need to generate your triangles on demand from the BREP data.
Alternatively you need to use tesselation, but then you need to design your models with tesselation in mind, such as people do in blender.
>Isn't this how any rendering will ultimately work? The primitive is triangles.
Uhm no. 3D printing and CAM do not work with triangles. The slicer and CAM software generate tool paths in gcode.
Importing STEP files into OrcaSlicer/BambuSlicer gives me better quality results and better print speeds than using STL files.
I have personally never understood the love for STL files in the 3D printing community for anything that isn't the result of a blender export. Like, is it really that fun to constantly export different versions of STL files set to different quality levels? Rescaling a print in the slicer is not recommended with STL. You have to re-export the model from blender where the tesselation happens.
