Topological Naming Problem(wiki.freecad.org) |
Topological Naming Problem(wiki.freecad.org) |
IIRC the FreeCAD solution tends to create names of ever-increasing length as you continue building.
That said, since v1.0, I've had far fewer instances of being affected, and have started doing some direct-on-face features (usually sketches) again.
The geometric kernel is doing boundary representation operations so when you do a boolean or a fillet, it doesn’t “edit” existing faces, it computes an entirely new b-rep from scratch. The old faces, edges, and vertices are gone and new ones are created to replace then. There’s nothing to hang a persistent ID on because the entities themselves are ephemeral.
There are solutions to the problem but they all break down eventually. I think freeCAD uses topological tracing and naming schemes so it encodes a face’s identity by how it was created. e.g., “the face generated by the intersection of extrude_1 and the XY plane.” The problem then is that parameter changes or operation insertions in the history can destroy those too, creating a new feature that can’t be easily mapped to the old ones. That’s where all the heuristics come in.
Unique IDs are used internally, but they only last for the lifetime of one evaluation. The hard part is establishing the equivalence between entities across re-evaluations when the topology itself may have changed.
Although… as others have noted, this is a problem with basically all CAD packages, as on a fundamental level, it depends on user design intent. Just some have enough bandaids that it’s more rare.
I’ve not encountered the same issue in FreeCAD 1.1 (to which I’ve transitioned recently). There are of course other frustrating niggles in FreeCAD, but not this one (yet).
> This problem is not unique to FreeCAD. It is generally present in CAD software, but most other CAD software has heuristics to reduce the impact of the problem on users.
Solidworks and Onshape don’t “hide” it better, their algorithms are better and break down in much more complex models than FreeCAD. Each one also tends to have its own quirks so as you learn to use the software you get a bit of intuition on how to best model certain features to avoid angering the topological naming gods.
I don’t think I’ve ever seen Solidworks break down in a simple model, it’s always been in complex shapes using advanced features.
Fusion 360’s heuristics are so good that I rarely run into these problems. When I do, it’s usually because it was a drastic change to a previous feature in the timeline and I’m expecting to encounter issues because it’s a really fundamental change.
Not trivial work.
The kernel FreeCAD uses doesn't really have a robust heuristic for this, so FreeCAD had to implement its own.
I'm not an expert, but these types of heuristics intuitively seem hard to model. The goal is to guess the user's design intent. There's often no single correct answer, it may require information from parts of the system that the core application's model doesn't have, there may be many heuristics depending on what's being designed.
These heuristics seem like exactly the sort of thing that commercial CAD applications can afford to spend resources on, and that open-source community-driven applications would struggle with.
No. Sorry, I should have been clearer. None of the open source programs handle this.
> These heuristics seem like exactly the sort of thing that commercial CAD applications can afford to spend resources on, and that open-source community-driven applications would struggle with.
This seems like one of those things where "the industry" converged to a solution and the people outside of it simply don't know what it is.
Read the article:
> https://wiki.freecad.org/Topological_naming_problem
"This problem is not unique to FreeCAD. It is generally present in CAD software, but most other CAD software has heuristics to reduce the impact of the problem on users."
So, the problem exists in (nearly?) all CAD systems, but in the big expensive commercial CAD programs, a huge amount of manpower was invested to hide the problem better to the user ("heuristics to reduce the impact of the problem on users") so that the users will see much more rarely see such a problem, and thus often won't be aware of the existence of the topological naming problem.
This isn’t just basic CRUD software that just needs some Postgres constraints to model trivial business logic. These are genuinely hard problems that mathematicians have been working on for decades.
There exists an insane amount of questions in topology that have (by our current understanding) nothing to do with CAD or even computational geometry.
> These are genuinely hard problems that mathematicians have been working on for decades.
The hard problems that mathematicians in topology work on are nearly always very different from what you think modern topology is about.
This fast renderer also closes and add hashed faces to cross sections views, instead of showing some buggy view of the inverts faces of the model.
Furthermore, the sketcher since mainline v1 is very laggy. Every click lags because its trying to draw the dimensions while you move them around but it's somehow slow and irritably laggy.
Finally in general, mainline also plenty of weird UI jitter and flicker. As if some code is fighting to resize elements back and forth during use.
Oh and the pie menu also wasn't copied either. On the realthunder fork a double press on "g" brings a menu under the mouse that quickly list the geometry near the cursor sorted by type, highlighting it as you hover on the selection. This is fantastic because of how bad freecad is at guessing what you are trying to select.
But mainline got a new color scheme and torturously slow UI animations that cannot be fully be disabled. This shows where are the priorities in my opinion.
To finish on a note of hope, at least I have noticed more open source projects using freecad rather than proprietary alternatives lately.
I treat FreeCAD as a rolling release, using the dev version on a decently complex model [0] and it has been a really good experience so far. Lots of useful features and fixees going in all the time.