RE: stl file comparison

From: Monica & Glenn Whiteside (
Date: Sat Jun 13 1998 - 07:42:49 EEST


What we have done to inspect various complex Stereolithography parts is to
obtain a point cloud (from CMM/Cordax machine) and then use a weighted
least-squares regression analysis based "best fit" software program to
compare this point cloud data back to the engineering surfaces. This "best
fit" software is an add-on function (originally developed by General
Dynamics) we have which runs within CATIA. It generates a report which
gives you the point identifiers and the deviations so you can track down
where the bad areas are. There always seems to be a few stray points that
can affect the data results but you can easiliy remove these from the model
and rerun the "best fit" program. Currently, this "best fit" program will
only work with surfaces, curves, or points, but why not add the capability
to also check your point scan data directly back to an STL file? (avoid
converting the scanned data to STL format for accuracy reasons). In the
spirit of "integrated" engineering, I happen to work right next to the
inspection individual who is the company expert on using this software if
you have any further questions. Also, I can get the company's name for you
and you can ask them directly.

There are currently inspection programs which can color map the part based
on point data, you can have different tolerances for different part regions,
and the different colors represent different deviations, and will
differentiate the undersized and/or oversized areas. This seems like it
could be an excellent visualization tool for inspecting complex RP patterns.

Hope this helps,


Glenn Whiteside
Cessna Aircraft Co.

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