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UGMENTALCASE  
#1 Posted : Wednesday, August 15, 2018 8:42:40 AM(UTC)
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Afternoon all,

So I have been working some wing point in Catia, which meant I need to create a spline between them all, then construct a surface between the two generated splines.
I thought, I could do this in VC. So I did, and then compared the results to that from Catia. Strangely enough they are 3mm different!!!!!
Now I'm no expert but I would've though they should come in the same? Same points, started the spline on the same point, to the same end point. Now a little difference I could handle but 3mm?
I wanted to put this on here saying look we have matched Catia with this task, but I'm not sure which I should be trusting. The area in question is a little funny, there is quite a gap between the first two points, however the rest of the points seem to tailor where it ends up. Any ideas? Any thoughts?

Edited by user Wednesday, August 15, 2018 8:44:03 AM(UTC)  | Reason: Not specified

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murray  
#2 Posted : Wednesday, August 15, 2018 5:29:32 PM(UTC)
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Degree or order of the splines? I mostly work in TurboCAD, which has provision to support curves up to degree 9, the higher the degree the more tension to the curve as I understand it, also as I understand it, each degree is essentially a factor in the polynomial function of the curve. I've also read that Rhino has the deepest curve support available commercially, up to 32 degrees, while IGES, for example, is limited to three or four-degree curves and surfaces. I've read also that higher degree curves can be closely matched by lower order/degree "piecewise approximation", while the US's Sandia National Laboratories produced some research that claimed that any curve in the presumed multiverse can be duplicated with a maximum 54 degree curve. Whaddya reckon? I think I've gathered more than enough hearsay over the years to be dangerous...
Check out Marcus Bole's PolyCAD app for some really good curve and surface handling and analysis. Registration needed but free, windows only.
UGMENTALCASE  
#3 Posted : Thursday, August 16, 2018 2:14:37 AM(UTC)
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The VC spline does appear tighter and I would be happier with that one and not the Catia one.
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NeuTechFLA  
#4 Posted : Thursday, August 16, 2018 3:44:21 PM(UTC)
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Originally Posted by: UGMENTALCASE Go to Quoted Post
The VC spline does appear tighter and I would be happier with that one and not the Catia one.


You might also be seeing translation accuracy differences. Meaning, I assume you imported one curve and then created the other native curve through the end points and internal nodes?

UGMENTALCASE  
#5 Posted : Thursday, August 16, 2018 3:47:07 PM(UTC)
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So I had the points in Catia, put a spline through them. Then imported everything to VC, and did the same again. So no show the Catia spline, so I was left with the points, and drew a new spline through the same points.
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murray  
#6 Posted : Thursday, August 16, 2018 9:42:59 PM(UTC)
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What transfer format did you use? VCP doesn't do native CATIA, does it? Shark does V4 & V5, but I don't know that it does anything other than solids. What CATIA are you using? Wanna see if Shark does anything different?
UGMENTALCASE  
#7 Posted : Thursday, August 16, 2018 11:47:36 PM(UTC)
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Exported igs from Catia, checked the coordinates of the points after import and all looked fine
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NeuTechFLA  
#8 Posted : Friday, August 17, 2018 4:53:36 PM(UTC)
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Originally Posted by: UGMENTALCASE Go to Quoted Post
Exported igs from Catia, checked the coordinates of the points after import and all looked fine


The deviation would not be the points as those are absolute. The curves are the issue. Either the order and/or type differences between the systems and of course the iges translation. This why we have, for years, used point clouds for body design. Translated curves leave too much ambiguity and clutter to deal with.

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