Data Segmentation

[Inspector_Gadget]

Does anybody know how Data Segmentation actually works in the Best-Fit alignment?  The documentation has this:

A check box that, when set, specifies automatically detecting high-discrepancy
areas before computing a final accurate alignment. Otherwise, all
Data points are used in the alignment computations.

BUT, I am just a little curious how it determines the high-discrepancy areas.  The reason is, sometimes it looks like my datum surfaces are being considered "high-discrepancy" areas and are being ignored in the best-fit alignment.  Does anyone have a good rule of thumb with when to use this option or not?

[prehistory]

In general, I don't think Data Segmentation is necessary during the Best-Fit.  However, if you are hoping to align with datum surfaces, you should probably do a datum-based alignment (3 perpendicular planes, plane-point-axis, etc.) instead.

Here's another trick though- if you have areas you know are throwing off your Best-Fit alignment, select them, the choose  >Ignore for Alignment which is under Image > Points in IMAlign, and under Edit > Data/Reference Element in IMInspect.

Version:  10.1.17

[PW User]

Hello,

The data segmentation will remove from the alignment all the data points that are further than the "Max distance" after the initial guess and then perform the best fit.

It can be harmfull if your datum surfaces are not well matched to the reference before the best fit starts its iterations. A few common reasons:
1- You partially scanned the part so the initial guess is not so good
2- You have a big deviation on the part so some areas are farther than the "Max distance"
3- A part of the table or fixture to hold the object still was scanned along with the real part, so the initial guess was also wrong.

In all cases, the AUTOMATIC initial guess within the best fit may be hte wrong thing to use, a MANUAL initial guess should then be performed with N-Point pairs.

Also, if you increase the "Max distance", the data segmentation will not remove as amny points befor performing the best fit.

Data segmentation is not NECESSARY and in V11, it was removed from the default checked parameters.

I check it on only when a jig was scanned along with the part and I perform a MANUAL initial guess using N-Point pairs.

Regards,
Bernard