[MetaCRS] Tolerance values in standard test format

[Landon Blake]

I think number 1 will be subjective and very difficult to quantify.
Different "authorities" may have slightly different formulas used in
conversion, and different software packages will implement these
differently.

How do I know how good Trimble Business Center conversions are compared
to AutoCAD Map or OGR2OGR?

I think we stick to clearly identifying the source of the expected
coordinate values in the test data file and let the user make a judgment
call. As an alternative, we could test various software packages and
provide a comparison of coordinate conversions, but I think this should
be done as supplemental information, and not as part of the test file.

I think you are correct about number 2. This should be library
dependent. However, if Martin Dre thinks a tolerance is important, I say
we include a suggested total 3D distance (between actual and expected
coordinates) tolerance.

Landon
Office Phone Number: (209) 946-0268
Cell Phone Number: (209) 992-0658
 
 

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org
[mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Martin Davis
Sent: Wednesday, November 04, 2009 2:35 PM
To: metacrs at lists.osgeo.org
Subject: [MetaCRS] Tolerance values in standard test format

Is the notion of "tolerance" actually conflating two different
requiremts?
 
1. Capture the accuracy of the test data as supplied from some external 
source.
2. Indicate the expected accuracy of a given implementation of a 
projection operation. 

#1 needs to be specified externally, obviously.  Possibly it could be 
indicated by the supplied precision of the expected value?

#2 would seem to be library dependent.

The definition of tolerance seems to be getting quite complex.  As Frank

says, it wouild be nice to move ahead with creating test artifacts even 
if the tolerance issue is not completely settled.

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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