PR# 259479 V44 Dimension/GDT Tests: The per-unit flatness does not seem to

huangyhg

<< Don Ruggieri  --  02/03/09  12:57:00>>
data is in 02032009_04a.zip   The per-unit flatness does not seem to directly respond to the step size.

Steps to reproduce:
I am testing dimeionsiona as part of the V44b test plan, specifically per-0unit flatness.  I am using the Hexagon plastic model, and programmed a plane on top.  I dimensioned the overall flatness and the per unit flattness of this plane with a step size of 10x10 and reporting to 5 decimal places.   The overall flatness reports as  0.18347 mm.  At first, with a 10x10 step, the unit flatness is 0.  With a 20x20 step, the unit flatness is still 0, out to 5 decimal places.  Even with a step of 25x25 the flatness is still 0.

Suddenly, when I change the step size to 30x30, the per unit flatness goes to0.00620.  Why does it make this jump from 0 to 0.0062?
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<< Don Ruggieri  --  02/04/09  10:24:19>>
Thank you for the explanation, I see it now.  I was assuming it would interpolate somehow.  I measured a smaller grid area with a tighter density.  When I change the step size, I see the measured per unit flatness responding more directly now, as I have the entire area covered with hits.  I will close this report.
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<< Changes made by Don Ruggieri -- 02/04/09  10:24:22>>
Status:  RESOLVED to CLOSED
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<< Don Turcotte  --  02/04/09  09:13:42>>
The area covered by the meas points of the plane is approx. 168 X 97 mm.  Given that there are only 24 points over this area, it is not surprising that the per unit flatness is 0 until you increase the per unit area to 30 X 30.   Increasing to a larger area gives a larger per unit flatness as expected.  
If you want to use a small per unit area such as 10 X 10 you will need a much greater point density.  If the number of meas points in any per unit area is less than 4, then the per unit flatness for this area is 0 indicating not enough data.
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<< Changes made by Don Turcotte -- 02/04/09  09:14:03>>
Action:  Don Turcotte to Don Ruggieri, Status:  OPEN to RESOLVED
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<< Changes made by Don Turcotte -- 02/04/09  09:13:42>>
Priority:  to Critical
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