[jira] [Created] (SIS-327) Defer loading of datum shift grid files

["Martin Desruisseaux (JIRA)" <ji...@apache.org>]

Martin Desruisseaux created SIS-327:
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             Summary: Defer loading of datum shift grid files
                 Key: SIS-327
                 URL: https://issues.apache.org/jira/browse/SIS-327
             Project: Spatial Information Systems
          Issue Type: Improvement
          Components: Referencing
            Reporter: Martin Desruisseaux
            Priority: Minor
             Fix For: 0.7


When a {{CoordinateOperation}} is created, its {{MathTransform}} is created immediately. This is usually not so costly, except in the case of datum shift based on a grid files where the grid files is loaded immediately. This is a waste of resources when the caller needs create many such operations, compare their {{domainOfValidity}} and retain only one operation at the end.

The proposal is to load the datum shift grid files only the first time that {{getMathTransform()}} is invoked. In addition to reduce the amount of resources to load, another effect of this would be to reduce the amount of warnings emitted because of grid files not present.

*How to reproduce:* the snippet below produces a lot of warnings if the grid files are not present. After this issue is fixed, we should have at most 1 warning.

{code:java}
CoordinateReferenceSystem sourceCRS = CRS.forCode("EPSG:4267");
CoordinateReferenceSystem targetCRS = CRS.forCode("EPSG:4326");
CoordinateOperation op = CRS.findOperation(sourceCRS, targetCRS, null);
{code}

*Note:* we could defer the creation of all {{MathTransform}} objects, but this is advantageous only for the cases where many operations exist between the same pair of CRS. This is the case of datum shift mostly.



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