Surface point measurement using SNAP=ON in secondary alignment

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  • Surface point measurement using SNAP=ON in secondary alignment

    I submitted a ticket on this already, but I want to make sure that I am understanding snap=on correctly. If I create and dimension a surface point in my |A|B|C| alignment all seems good as in the first picture shown (SnapOnMeasuredAndDimensionedInABC.jpg). Non-check directions show zero deviation. All is good.

    However, If I create another point or series of points in a 'sub' alignment or 'local' alignment, my actual (non-check direction) measurements will show deviation, even with SNAP=ON as shown in the second picture (SnapOnMeasuredInSubAlignmentButDimensionedInABC.j pg).

    Is this operating as designed or am I correct to assume that I should see zero deviation using SNAP=ON in both the measurement and the dimension regardless of the alignment?

    Thank you kindly for the input.
    Attached Files
    Last edited by johnnyrocket; 08-01-2019, 09:51 AM.

  • #2
    I believe the snap=on is just for when the point is measured. If you dimension the points in a different alignment, I can see the values being off by the amount the alignment features are off.

    The nominal values in any given alignment are basically a stackup of all the nominal values of alignment features going back to the original alignment features. Kind of like how basic dimension work. The measured values are strictly relative to the measured values of the alignment features for the alignment your reporting in.
    PC-DMIS 2016.0 SP8

    Jeff

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    • #3
      Originally posted by Schrocknroll View Post
      If you dimension the points in a different alignment, I can see the values being off by the amount the alignment features are off.
      Schrocknroll, yes I can see now where the error is coming from. It is a direct result of how far off the secondary alignment feature deviates from the original alignment. It does seem quite odd that it would not report the actual deviation relative to the localized alignment. Seems like that is the whole point. The problem with this is that using snap=on or snap=off would make no difference, you will still see deviation in your non-check directions for features that are not measured and dimensioned in the original alignment.

      Seems that the deviation of any features measured should be absolutely recorded according the alignment from which they were measured.

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      • #4
        Originally posted by johnnyrocket View Post

        Schrocknroll, yes I can see now where the error is coming from. It is a direct result of how far off the secondary alignment feature deviates from the original alignment. It does seem quite odd that it would not report the actual deviation relative to the localized alignment. Seems like that is the whole point. The problem with this is that using snap=on or snap=off would make no difference, you will still see deviation in your non-check directions for features that are not measured and dimensioned in the original alignment.

        Seems that the deviation of any features measured should be absolutely recorded according the alignment from which they were measured.
        Measurement results, which include deviations, will always be relative to the alignment in which they are dimensioned. If you want the results relative to the alignment in which they were measured you can always recall that alignment before you create the dimension.
        PC-DMIS 2016.0 SP8

        Jeff

        Comment


        • johnnyrocket
          johnnyrocket commented
          Editing a comment
          Schrocknroll, I found a parameter that does what I need it to do when dimensioning location points in another alignment. Do you have any experience with RETROLINEARONLY/ON ?? Seems to apply "SNAP" functionality to the dimension itself.

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