[MetaCRS] Standard (and simple) format for conversion tests.

[Landon Blake]

Martin D wrote: " Suggesting a tolerance can make the job easier for the tester (one less thing to  think about), especially since the tolerance depends on the unit of measurement, the proximity of pole in case of geographic CRS, whatever the operation involve  a datum shift or not (to phrase that in ISO 19111 terms: whatever the operation  is a "conversion" or a "transformation"), etc. However I'm fine with either approach (including or excluding them from the test file)."

OK. A suggested tolerance is probably a good idea. We then need to pick which one of the following to use, or list them all:

X Tolerance
Y Tolerance
Z Tolerance
2D Distance Tolerance
3D Distance Tolerance

Martin D wrote: "If we define "X" and "Y" as "first and second axis in a right-handed system", I'm fine. We can not said "X=Easthing and Y=Northing" (except informaly) because it doesn't work at poles (e.g. Polar Stereographic projections), while a right-handed system is well defined everywhere"

OK. We can specify the meaning of X, Y, and Z in the file format spec. I should have clarified my use of these terms for our discussion. In my use "x" meant easting in a grid system or longitude in a geographic system. "Y" meant northing in a grid system or latitude in a geographic system. Z meant height or elevation. Of course, I am a surveyor, so I like northing, easting, elevation. :]

If X, Y and Z is to "grid specific" we could just require that the test name each ordinate value. So instead of something like:

X:6522188.12 Y:2558223.12 Z:23.255

Latitude:37-15-02.356 Longitude:-121-52-45.233 Ellipsoid_Heiht:120.23

Or:

Northing: 2558233.12 Eastng:6522188.12 Elevation:23.255

This frees the data file from having to worry about enforcing a certain ordinate order. We can just label the ordinate values. That would allow us to expand the number of ordinates used to specify coordinate values in the future. Down the road we could then do something like this:

Northing: 2558233.12 Eastng:6522188.12 Elevation:23.255 Epcoh_Date:1991.35

Landon
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-----Original Message-----
From: Martin Desruisseaux [mailto:martin.desruisseaux at geomatys.fr] 
Sent: Wednesday, November 04, 2009 1:44 PM
To: Landon Blake
Cc: metacrs at lists.osgeo.org
Subject: Re: [MetaCRS] Standard (and simple) format for conversion tests.

Landon Blake a écrit :
> Martin D wrote: " Maybe the tolerance should be specified for each axis, instead than one value applying to all axis. This is more useful when the target CRS is a geographic one, since the tolerance on longitude can become greater as we approach the pole. At the extreme case (point a North pole or South pole), the longitude is meanless and should have a tolerance of +/- 180"
> 
> Now that I think about it, why have the tolerances specified in the test data files at all? Let the programmer writing the tests that will use the files set his own tolerance values and determine which tolerance is most important to him/her.

Suggesting a tolerance can make the job easier for the tester (one less thing to 
think about), especially since the tolerance depends on the unit of measurement, 
the proximity of pole in case of geographic CRS, whatever the operation involve 
a datum shift or not (to phrase that in ISO 19111 terms: whatever the operation 
is a "conversion" or a "transformation"), etc. However I'm fine with either 
approach (including or excluding them from the test file).


> Martin D wrote:" Maybe the axis order should be "as the authority said" (useful for testing libraries to be used with recent WMS/WCS versions), instead than forced to "X Y Z" order. As a help for libraries that do not handle axis ordering, we could add a field telling what the order is for the current record."
> 
> Good point. So maybe we do something like this:
> 
> X:60321125.25 Y:2335688.21 Z:12.20

If we define "X" and "Y" as "first and second axis in a right-handed system", 
I'm fine. We can not said "X=Easthing and Y=Northing" (except informaly) because 
it doesn't work at poles (e.g. Polar Stereographic projections), while a 
right-handed system is well defined everywhere.

	Martin



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