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Auto-Cylinder vs Circles Constructing a Cylinder: For Perpendicularity

cmmGrum
Which is more accurate, the auto-cylinder to plane OR 3 auto-circles (constructing a best fit, least squared, cylinder) to plane.

Essentially they should have the same result, correct?

When I run it I have a 0.0009 difference between the results.

Which number should I trust?

(I am building off of an IGES file)

Looking at previous posts I made sure that I had it set to Perp to Datum
  • , how do you use Cir1.hit[1..numhits]? I'm using basic circle scans to construct circles along a cylinder. Then I'm constructing a cylinder using the circle constructions I made to get an overall dimension. Would using Cir1.hit[1..numhits] make the constructed cylinder more accurate?
  • , how do you use Cir1.hit[1..numhits]? I'm using basic circle scans to construct circles along a cylinder. Then I'm constructing a cylinder using the circle constructions I made to get an overall dimension. Would using Cir1.hit[1..numhits] make the constructed cylinder more accurate?

    In the case of basc scans, the constructed feature uses the hits directly.
    For an autofeature using scanning options, the centroid can be used by default (in this case, you can create an axis)
  • in reply to acgarcia
    see jefman's explanation below. Basically I stand corrected, by the master himself Smiley
  • Glad to know that i'm doing this right, what exactly is Cir1.hit[1..numhits]? some sort of array?
  • (Cylinder Construction)

    Constructing a cylinder from circles seems to be a special case in PC-DMIS, as this will always use the hits from the circles, not the center points! Can easily be seen by constructing a cylinder from a circle pattern. A cylinder from the four center points would not have a form error of 14.2701 (and would not have 12 hits)... 

    CYL1       =FEAT/CYLINDER,CARTESIAN,OUT,LEAST_SQR,NO
            THEO/<123.857,50,0>,<0,0,-1>,86.921,0
            ACTL/<123.857,50,0>,<0,0,-1>,86.921,0
            CONSTR/CYLINDER,BF,CIR1,CIR2,CIR3,CIR4,,

            ASSIGN/V1=CYL1.NUMHITS



  • in reply to acgarcia
    its a method to force pcdmis to include all individual points in whatever you are intending to use it within. In this example, if you created the circle feature using autofeatures, then call the circle to construct an axis line or a cylinder, it will only pull the autocircle's centroid point. you can use the cir1.hit[1..numhits] to get away from the centroid, and instead it would use all the point data that is being measured in that autofeature
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