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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SIS-369) Better selection of datum shift method depending on desired accuracy
Date Wed, 25 Oct 2017 19:09:00 GMT
Martin Desruisseaux created SIS-369:
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             Summary: Better selection of datum shift method depending on desired accuracy
                 Key: SIS-369
                 URL: https://issues.apache.org/jira/browse/SIS-369
             Project: Spatial Information Systems
          Issue Type: Improvement
          Components: Referencing
    Affects Versions: 0.8
            Reporter: Martin Desruisseaux
            Priority: Minor
             Fix For: 1.0


Coordinate operations may be slow, especially when datum shifts are involved. When not using
datum shift grid files, the most common method is _geocentric translation_. The _Molodensky_
method is a little bit faster at the expanse of accuracy, but that accuracy lost may be acceptable
for example if the scale on a map is not sufficient for seeing the difference. At very small
scale where each pixel is 10 km wide, we can even skip the datum shift operation completely.
The question is where to put the threshold. 5 meters for _Molodensky_, 10 meters for _Abridged
Molodensky_, 3 km for none? This need to be measured, for example by trying all _geocentric
translation_ operations in the EPSG database. Once thresholds have been determined, the {{DatumShiftMethod.forAccuracy(double)}}
method should be updated accordingly.




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