Full Version: Wrong import of trimmed IGES surface.

Hi I made this model as an exercise with FreeCAD, but when I tried to import this IGES model I have an incorrect display of the edge of the cut surface. 
the file is attached.



With CAD assistant the result is good and also with others viewers





and here others viewer of this IGES

Attachments:
W.Garden_Isaland_tender.iges.tar.xz

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Hi pafurijaz, thanks for posting the file.

The geometry of the trim curves for the inner hole on this model is of very poor quality.

I tested some in Rhino and what initially appears to be an inner trim boundary made up of 5 edges is actually one long edge (and one tiny micro edge) that has an extremely tight awkward bend in it at what should be sharp corners:







There are also oscillations around those pseudo-corner spots:



I'm not sure exactly what is going on but I think it's probably so close to being non-G1-continuous that it's causing some problems in MoI in some of the algorithms that involve stepping along curves.

But the edge geometry here is of such very low quality that I doubt that it will be able to be fixed up automatically.

- Michael

Image Attachments:
pafurijaz_hole1.jpg  pafurijaz_hole2.jpg  pafurijaz_hole3.jpg  pafurijaz_hole4.jpg 

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Thanks Michael, I understand the problem however, I hope you can find a solution to this particular problem considering that in other applications the problem dosen't occurs, I have made this with curves created with low precision since I am not good at using FreeCAD, I will do it again the model with better parametric curves and trying to keep the geometry clean.



Greetings

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Hi pafurijaz, various problems are bound to occur in other apps too with this kind of very poor quality trimming geometry. It's just a matter of luck that MoI's UV to 3D edge curve push-up gets messed up in particular. If you tried to do other things with the geometry in those other apps than just viewing it you'll likely run into more problems there too.

Sorry, I don't think it will be feasible to fix it, it would involve changing some low level curve stepping processes which are risky to mess with, it's really easy to break other cases.

Somewhere along the line in FreeCAD it seems to have glued curve pieces together in some way that didn't preserve the sharp corners.

- Michael

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OK Michael, I started creating surfaces by improving my workflow, and now things seem to be working better, the previous model was done in a messy way and I was partly aware of it, this is a new one with clean surfaces and regular cuts .

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