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Alignment Features and Location vs Position

MaLux
hello,

simple basics but i am not sure.

the ISO drawing callout's for GX circles, so i wrote the program only using GX circles... If i am not wrong the xact measure position calculation is also automatically using GX, even If the element is measured as GG ?!

Is this the right way, or should the alignment be GG to be more stable and measure the Elements a second time with GX, since our PC-DMIS 2017 and Q-DAS Converter can't output the Dimension when using Size for GX...

What i also can't figure out is, that the X,Y Location even with measured GX Features and alignment are not matching the XAct Location... ConfusedConfused

Perp. to centerline and the axis are checked so what could cause the deviation between the Position and Coordinates ?


Thanks in advance.
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  • XactMeasure (and Legacy Dimensions) use the pre-resolved feature so, if you have measured your circles using a particular math type, that is what the calculation is based on. The only time features are re-calculated is when it is an XactMeasure form tolerance (flatness for example) in which case it uses the Chebyshev calculation.

    As for alignments, GX (maximum inscribed) is known to be mathematically unstable in certain cases and can lead to poor repeatability. It is especially limited when you have partial arcs rather than full diameters or when the form error of the hole makes it more of an oblong shape than a true circle. Your alignments would definitely be more stable if built from least squares features but you would then have the problem that the X Y & Z locations based on those alignments would not match those in the XactMeasure dimensions reporting GX features - as you have found. That is because the least squares calculation would yield a different centroid and size for the circle than the GX calculation would.
  • in reply to Neil Challinor
    Hey Neil,

    thank you for your answer.

    One of my Problems is, that even with GX Alignment and GX Features the X,Y,Z is Not matching the Position.
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