Transfering IGES from cimatron to rhino - naked edges and bad surfaces

Rhino Rhino for Windows
21

Which begs the question… oh never mind

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@GregArden

Hi Greg, I have an example hull from Maxsurf that displays all the behavior that we have problems with when sectioning the surfaces.

BadSurfacesMaxsyrfExample.png1274×647 95.7 KB

I have sent you the 3DM file with the upload facility on rhino3d.com.

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Hi Danny- most likely that surface has stacked control points… Intersections still do not handle all of these cases.

-Pascal

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I just thought it would be good for you guys to have an example of what MaxSurf is producing. This particular one is such a geniric example. There are no secrets shrouding it from third party eyes.

This Hull has no chines and I suspect that it’s the trimming that causes the erroneous issues.

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Danny,
Was this imported into Rhino as an IGES file? If so do you have the IGES file. If it wasn’t an IGES file how did it come into Rhino?
Greg

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Hi Danny, does it change something if you use _RemoveMultiKnot on those surfaces ? Just curious…

c.

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@GregArden, the file has been uploaded.

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Hi clement,

Using the _RemoveMultiKnot command resulted in “14 objects had no multiple knots”

29

Danny,
Thanks for the file. It appears the problem is importing into a Rhino model with units of millimeters the model must be scaled. We don’t properly scale some of the tolerances and then the intersections don’t work.

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And there’s me been slagging MaxSurf off all this time :smile:

Glad you have got to the bootm of this.

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Even with the edge tolerances properly scaled, there are still problems. This is because the model was built at an accuracy of 0.001 m, then brought into a file that expects an accuracy of 0.001 mm.

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Hi Chuck,

What is the correct approach? I/we often have no control of the generation of the Input IGES and its tolerances.

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I guess it depends on what you’re trying to do. If all you want is to get contours from the model in the IGES file, then just open the file rather than import it. Then the model units would be meters and the tolerance would be that of the IGES file. If you need to be working in mm rather than m because you will be adding small details, then maybe try to do all of the large scale things in m, and switch to mm for the details. This should be OK as long as your details don’t run into the edges of the larger model. It could be that the gap between large surfaces is as large as your detail.