[geotk] [JIRA] Created: (GEOTK-71) Conversion from CompoundCRS[ProjectedCRS + VerticalCRS] to a 2D CRS should detect when no datum shift is needed

[Martin Desruisseaux (JIRA)]

Conversion from CompoundCRS[ProjectedCRS + VerticalCRS] to a 2D CRS should detect when no datum shift is needed
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                 Key: GEOTK-71
                 URL: http://jira.geotoolkit.org/browse/GEOTK-71
             Project: Geotoolkit
          Issue Type: Improvement
          Components: Referencing
    Affects Versions: 3.06
            Reporter: Martin Desruisseaux
            Assignee: Martin Desruisseaux
            Priority: Minor
             Fix For: 3.07


Conversion of {{sourceCRS}} to {{targetCRS}} fails when the CRS have the following characteristics:

* The {{sourceCRS}} is a tree-dimensional {{CompoundCRS}}, made of a {{ProjectedCRS}} with a {{VerticalCRS}}.
* The {{targetCRS}} is a two-dimensional {{GeographicCRS}}.
* The {{sourceCRS}} and {{targetCRS}} use different datum. *Nevertheless, all Bursa-Wolf parameters are declared equal to 0*
* The {{VerticalCRS}} in the {{sourceCRS}} does *not* measure height above the ellipsoid.

The current behavior is to fail with an exception like the one below:

{noformat}
org.opengis.referencing.operation.OperationNotFoundException: Aucune transformation du système "CompoundCRS[ETRS89 + Sigma level]" vers "GeographicCRS[WGS 84]" n'est disponible.
        at org.geotoolkit.referencing.operation.DefaultCoordinateOperationFactory.createOperationStep(DefaultCoordinateOperationFactory.java:1205)
        at org.geotoolkit.referencing.operation.DefaultCoordinateOperationFactory.createOperation(DefaultCoordinateOperationFactory.java:349)
        at org.geotoolkit.referencing.operation.CachingCoordinateOperationFactory.createOperation(CachingCoordinateOperationFactory.java:222)
        at org.geotoolkit.referencing.operation.CachingCoordinateOperationFactory.createOperation(CachingCoordinateOperationFactory.java:251)
        at org.geotoolkit.referencing.CRS.findMathTransform(CRS.java:1221)
        at org.geotoolkit.referencing.CRS.findMathTransform(CRS.java:1185)
        at org.geotoolkit.referencing.operation.WithEPSG_Test.testProjected3D_to_2D(WithEPSG_Test.java:93)
{noformat}

This is the wanted behavior, because accurate conversion require first converting the "sigma-level" height (or any non-standard height) to ellipsoidal height before to apply the datum shift, and in the test case used above the referencing module doesn't know how to perform this height conversion.

However in the special case where the height is going to be dropped anyway in the {{targetCRS}} and when the (_latitude_, _longitude_) are not affected by the datum shift because all Bursa-Wolf parameters are explicitly set to 0, it is correct to process anyway. We should allow the referencing module to detect such special case.


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