I’m dealing with a CAD model provided by a company that was probably made in Solidworks. There are plenty of bad objects: self-intersecting surfaces, chaotic control points (like one surface is less than 1 mm small, but its control points are spread to 20 meters away), adjacent surfaces forced to be be joined despite the huge gap in-between. Really bad everything.
Some of the bad surfaces can’t be untrimmed via the ! _Untrim tool in Rhino, nor they could be modified by changing the degree and control points count. If I remember correctly, a few years ago @pascal posted some script that enabled untrimming of “untrimmable” surfaces. Does anybody know a solution?
I upload one of those bad surfaces here as a reference.
Untrimmable bad surface.3dm (133.1 KB)
i am not sure what is going on, it does not display the surface but only the edges, no matter what i do, till i untrim it.
one thing i noticed is that this surface is very tiny, about 1 mm across, still it seems to untrim alright using untrimall. (using mac v8)
but i can feel you there, i (thankfully only once) had to deal with a model from solid works (or so i thought) and the surfaces were straight from the garbage bin. i am not sure why but i had the feeling that their strange tolerance settings may be causing that stitching any crap together that usually would fail in rhino.
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This was quite puzzling, so I randomly tried test commands that I have in my notes, and the TestSeamOpener did untrim the surface and also make it valid.
I also noticed that you can click the surface a second time while in the command, and it will open up the singular edge, which is kind of interesting on its own.
I have no idea why this worked.
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Thanks for the suggestion! No matter how many times and where I click on the surface, it will never untrim in my Rhino 7. However, once I tried the TestSeamOpener command, the surface was untrimmed successfully.
The “Untrim all” command does not help on this surface, at least on my Rhino 7. This particular surface caused several crashes today and I was wondering why it’s so untrimmable. Most likely there is some self-intersecting trimmed region. Just a suggestion.
By the way, you are totally right about models with fillets made in Solidworks. They are the worst when it comes to tolerances and fake joining of obviously distant surfaces with big gaps in-between. Somehow Solidworks cheats by stitching together edges that are supposed to produce large seams. I also have one video showing the issue. The end result does not correspond with the preview. This is a common thing in SW:
Here is another (of many) bad surface made in Solidworks that I was forced to delete and replace with a proper surface made in Rhino. For reference, the original file was 1,5 GB large and saving it took 18 minutes. The fixed model is 339 MB and saves for less than 10 seconds. The only difference is that I replaced more than 50-60 tiny surfaces that had self-intersections, unnecessary amount of control points, and/or forced joints despite being way far from each other.
In my post I meant that if you click the surface second time while in the TestSeamOpener command, it will open up the singular edge of the surface. Untrim did nothing for me either.
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I already tested that, but I used the Command line options instead. 
Nice little touch.
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