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When to use Primary Datum Plane construction

JFournier
The newer version of PC-DMIS has a constructed plane option of Primary Datum Plane, and I'm not sure when I should be using that.

Should it be used in my DCC alignment for the primary (leveling) datum?
Or should I continue to use the auto-feature plane that defaults to LSQ for alignment, and use the constructed Primary version as a Datum Definition that is used for evaluating GD&T only?

Is there any concern that if I don't use enough points to construct this Primary Datum plane, it will skew alignments/results if there is too much part variability and the points aren't exact from part to part? (example: if there's an errant hit on a burr or something, the plane is far more skewed compared to an averaged plane)







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  • I dont use Geotol but my understanding is that your primary datum plane sets your A datum for that program so you can use it for alignments and dimensioning. Everything checked to "A" is referenced back to that feature.
    • L1 - This is equal to the sum of the distances.
    • L2 - This is equal to the square-root of the sum of the squares of the distances. Minimizing the L2 norm is the same as a least-squares fit.
    • L∞ - This is equal to the maximum distances between the ideal surface and the non-ideal surface. Minimizing the L∞ norm is the same as minimizing the maximum deviation, so we use the term "minmax" for this norm.
    Please correct me if I am wrong.
    ​
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  • I dont use Geotol but my understanding is that your primary datum plane sets your A datum for that program so you can use it for alignments and dimensioning. Everything checked to "A" is referenced back to that feature.
    • L1 - This is equal to the sum of the distances.
    • L2 - This is equal to the square-root of the sum of the squares of the distances. Minimizing the L2 norm is the same as a least-squares fit.
    • L∞ - This is equal to the maximum distances between the ideal surface and the non-ideal surface. Minimizing the L∞ norm is the same as minimizing the maximum deviation, so we use the term "minmax" for this norm.
    Please correct me if I am wrong.
    ​
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