How to calculate true position using variables and expressions

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  • How to calculate true position using variables and expressions

    I am new to variables and expressions. I cannot find what i'm looking for in the help index. Does anyone know how to do this?

  • #2
    In the Edit Window, type ASSIGN and press TAB. You will have a command "ASSIGN/V1=0". Press F9 on the command, and click "Assign From...". This will take you to the Expression Builder which is a great place to start looking around.


    • #3
      Jacob, i've been there but havent had any luck creating a true position calculator. i was hoping someone here has done or tried to do the same thing.


      • Mike Ruff
        Mike Ruff commented
        Editing a comment
        Why not just use Insert> Dimension> Position? Why create extra work for yourself unnecessarily?

    • #4
      Depending on the axes that you are evaluating your positional tolerance in, let’s say X and Y, you would assign deviation variables, dx and dy, respectively, as


      And you would calculate your positional error as

      ASSIGN/POS=2*SQRT(DX^2 + DY^2)

      You have to be sure that your active alignment matches your DRF exactly or this won’t work. Also, as has been mentioned, if you have the tools to properly compute a positional error using the rules of your applicable standard (XactMeasure), then you should do that.

      What is your reason for attempting this manually through variables?


      • commented
        Editing a comment
        Also, this calculation won't include the theo/meas vector...

      • JacobCheverie
        JacobCheverie commented
        Editing a comment Very good point, this would only apply in a 2D case. Thank you.

    • #5
      I have a part that has four rails.(imagine a dvd rack) the drawing is treating the inside of the four rails like a circle when it isn't. the rails are actually square. i've tried constructing a circle from a point on each rail but pc dmis isnt having it so i wanted to use the deviation of the points coming from center ( rotating my alignment accordingly) and calculate a true position with the worst two deviations. sounds like alot because it is.


      • neil.challinor
        neil.challinor commented
        Editing a comment
        Have you tried measuring them as square slots?

    • #6
      the shape of the feature collectively wouldnt be square, it would be circle but PC DMIS wont recognize it as a circle. I did come up with a way to calculate the true position based off of what Jacob commented on above. thank you guys for your help.


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