Dimensional Measuring Interface
Standard
Standard Improvement Request
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SIR No. 97-52 DMIS Release 3.0 SIR Type Error Severity Wrong Result / Interaction Status Resolved Date Submitted August 12 1997 Date Validated August 12 1997 Date In Process Date Referred Date Vote Pending Date Closed April 1 1998 Action Clarifications Submitted By Thomas Kramer NIST Room B-124, Bldg. 220 Gaithersburg MD 20899 USA Phone: (301)975-3518 Fax: (301)990-9688 kramer@cme.nist.gov |
Problem Topic
POL: Clarification on use of polar coords
Problem Description
The treatment of "polar" coordinates is difficult and awkward, and may be
incorrect, depending on what the documentation, which is unclear, means.
The statement which causes the problem appears on page 35 as a note. The same statement (or variants of it) appears also on pages 47, 56, 60, 65, 67, 69, 208, and probably many other places. The statement on page 35 reads:
"The x,y,z point coordinates and i,j,k vectors are given relative to the active part coordinate system. The r and a values are also given relative to the active part coordinate system. The h value is the perpendicular distance of the point from the WKPLAN."
This could be taken to mean that the r and a values are always given in the XY plane of the active part coordinate system. If this is the case, however, polar coordinates fail when the WKPLAN is the YZ or XZ plane; in those cases, the polar coordinates of a point describe a line, not a point, and the h value is determined by the r and a values.
Since the first possible interpretation leads to an unusable system, I take it that the interpretation is incorrect.
A second interpretation is that the quoted statement means:
"The x,y,z point coordinates and i,j,k vectors are given relative to the active part coordinate system. The r and a values are given relative to the active WKPLAN of the active part coordinate system. The h value is the perpendicular distance of the point from the WKPLAN."
This second interpretation is consistent with the final paragraphs of page 33. The second interpretation also gives a workable coordinate system.
If the second interpretation is correct, the wording should be changed as shown every place the statement appears.
If the second statement is correct, however, it is necessary to record both the active coordinate system and the active WKPLAN when a feature is defined in order to have a full description of what is intended.
References
None
Related SIRs
None
Suggested Resolution
I would prefer having "polar" coordinates be standard mathematical
cylindrical coordinates using r and a in the XY plane of the active part
coordinate system and using z (not h) of the active part coordinate system.
With this method, it would be irrelevant which plane is the active
WKPLAN.
My second choice would be to have the wording of the note changed (everywhere it appears) as shown above.
Support Documentation
None
Resolution
Warning!!
The following statement is only a resolution to a Standard Improvement Request (SIR) and is NOT part of the current DMIS standard, nor is it guaranteed to become part of the next revision of the DMIS standard even if voted and accepted by the DMIS National Standards Committee. This resolution is tentative because it may not be incorporated into the next version of the standard, it could be changed prior to the next release, or it could be changed as the result of the "public review and comment" period required for the next version of the standard. If you choose to use this tentative resolution, you do so at your own risk since at this time it is not part of the DMIS standard.
Attachments
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Notes
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