Cloud to CAD Best Fit vs Best Profile

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Tabor
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Cloud to CAD Best Fit vs Best Profile

Post by Tabor » Tue Mar 08, 2016 3:50 pm

I have a profile that is only constrained by one datum (rotation in X,Y and translation in Z) so I'm reporting a C2C with best fit with the proper freedoms of movement constrained. It reports out but when I looked at the graphical report, I noticed that it was out only in one spot and there was room to shift it up. By doing so, I was able to make the profile conform. I think I already know the answer but is there any way to do a C2C that will report the Best Profile instead of best fit?
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US_Helpdesk
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Re: Cloud to CAD Best Fit vs Best Profile

Post by US_Helpdesk » Fri Mar 11, 2016 12:24 pm

Did you try to increase the accuracy level of Best Fit? Turn it up to 9 and see if the fit improves.
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Re: Cloud to CAD Best Fit vs Best Profile

Post by Tabor » Fri Mar 11, 2016 1:44 pm

I did, and I don't think it's a matter of accuracy. I don't know anything about the underlying code, but I'm guessing best fit would fit based on something like an RMS of the deviations and wouldn't pay any attention to the desired profile. If only a small area were out, the weight those points would carry would be negligible compared to the rest of the part. In my situation, most of the part was close to nominal after best fit but there was one small feature that was a couple of thousandths over my allowed profile (±.005"). Since the other side was close to nominal, I was able to translate the part up a couple of thousandths and make the profile conformant but now there were a lot of points on the other side of the part that while in profile, were farther from nominal.

I'm a little tired so I hope that all made sense.
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Re: Cloud to CAD Best Fit vs Best Profile

Post by US_Helpdesk » Mon Mar 14, 2016 2:50 pm

You're right... The Best Fit method is RMS (tries to reduce the sum of all deviations) Another Fit method might try to reduce the overall form error. These types of fitting algorithms are available for features (Least Squares, Min/Max, Max Inscribed, Min Circumscribed, etc.) but not for Cloud to CAD since the surfaces are not always geometric with these comparisons.

If you want to further "improve" the best fit from Cloud to CAD report you might use VB Script to find min and max points then somehow translate the Ref Frame to split the difference. If it's just a simple translation of Ref Frame you could even do the math in Excel instead of VB Script.
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Re: Cloud to CAD Best Fit vs Best Profile

Post by Tabor » Mon Mar 14, 2016 5:39 pm

That's an interesting thought and it could definitely work. It's not something we see very often though so it might not be worth the trouble. Also, this part is on the iNexiv so we're talking 1k+ points and I imagine a VB loop would grind on that for a while.
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