Dimensional Measuring Interface
Standard
Standard Improvement Request
|
SIR No. 97-26 DMIS Release 3.0 SIR Type Other Severity Interpretation Request Status Resolved Date Submitted March 6 1997 Date Validated March 6 1997 Date In Process Date Referred Date Vote Pending Date Closed August 20 1998 Action Clarifications Submitted By Dietmar May Object Workshops, Inc. PO Box 597 Whytheville VA 24382 USA Phone: (540)223-1145 Fax: (540)223-1241 dcmay@object-workshops.com |
Problem Topic
POL: Scoping of coordinates?
Problem Description
Are POL coordinates relative to current Part Coordinate System origin? What
happens to POL coords if a FEAT is defined in one PCS and output in another?
References
None
Related SIRs
None
Suggested Resolution
A POL coordinate is just as meaningful a description of a single point in 3D
space as a CART coordinate, BUT ONLY WHEN COUPLED WITH A PCS AND WORKPLANE.
There is a single point which is defined by a POL coordinate at the time a
FEAT is defined. It would seem disasterous for a FEAT to move when the
coordinate system or workplane is changed, because a PCS change does NOT alter
the physical location of the FEAT in space. It would be impossible to use that
FEAT in constructions or or other calculations if its coordinate were to change
when a new PCS was established or the workplane was changed.
Therefore, it seems that the POL coordinate needs to represent the point in
absolute 3D space which it represented at the time it was first applied (eg.
when a FEAT definition statement was executed). The DME sofware can handle this
in several ways: for instance, associating the PCS and workplane at the time of
use or definition and converting to the current PCS and workplane when the
coordinate is output or used (as in a CONST); converting the coordinate to a
known, neutral, absolute coordinate system when defined and converting to the
current PCS and workplane when the coordinate is output or used); or converting
all POL coordinates to the current PCS each time a new coordinate system is
established.
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.
Add paragraph to section 3.2.2 and text to section 5.2.
Add the following text in section 3.2.2, following the third(3) paragraph.
"Feature nominal coordinates shall retain their original values during any subsequent coordinate system transformations, with nominal values unchanged throughout the execution of the system. Therefore, a nominal coordinate is not directly associated with or expressed in any coordinate system; however, the nominal coordinate shall be utilized as a location relative to the origin of the current coordinate system at the time it is applied. Conversely, feature actual coordinates always reference the same absolute location within 3D space, but are transformed (when used) into the current coordinate system."
Also add to the text on page 111 section 5.2 after the third(3) paragraph: "See section 3.2.2 for more information about the relationship of coordinate systems to features."
Finally, it was recommended that an enhancement SIR be proposed to add a new major word, such as NOMUPD/[ON,OFF], which would control a modal setting within the DME software. When off, the DME should operate in the mode as specified in the clarification above. However, when the nominal is first applied (as in MEAS), the current part coordinate system would be associated with the nominal feature. then, during subsequent uses of the feature nominal, if the nominal update setting is on, its coordinate would be transformed into the coordinate system that is current at the time of use.
This modal nominal update setting should apply only within a carriage common section
This needs to be formally proposed as an SIR.
Attachments
None
Notes
Added by Interpretation Sub-Committee, gph5@chrysler.com on 8/4/1998
Suggested final resolution is to put the proposed resolution text in section 3.2.2, following the third(3) paragraph.
Also add to the text on page 111 section 5.2 after the third(3) paragraph: "See section 3.2.2 for more information about the relationship of coordinate systems to features."
Added by Dietmar May, dcmay@object-workshops.com on 9/3/1998
The recommended enhancement SIR should not be submitted, since a subsequent SIR 98-1 established that nominal updating does not apply.