[jira] [Created] (SIS-536) Infer default datum from ellipsoid

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

Martin Desruisseaux created SIS-536:
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             Summary: Infer default datum from ellipsoid
                 Key: SIS-536
                 URL: https://issues.apache.org/jira/browse/SIS-536
             Project: Spatial Information Systems
          Issue Type: Improvement
          Components: Referencing, Storage
    Affects Versions: 1.1, 1.0, 0.8
            Reporter: Martin Desruisseaux


When reading a GeoTIFF file (but could also happen with other sources), the datum name is sometime unspecified. The problem is that the datum name is important for determining if two datum should be considered equal. As an alternative, we could use one of the EPSG codes for unspecified datum. There is currently 40 such datum:

{code:sql}
SELECT datum_code, datum_name FROM "EPSG"."Datum" WHERE datum_name LIKE 'Not specified%' AND deprecated=FALSE
{code}

||Code||Name||
|6019|Not specified (based on GRS 1980 ellipsoid)|
|6013|Not specified (based on Clarke 1880 (Arc) ellipsoid)|
|6014|Not specified (based on Clarke 1880 (SGA 1922) ellipsoid)|
|6015|Not specified (based on Everest 1830 (1937 Adjustment) ellipsoid)|
|6016|Not specified (based on Everest 1830 (1967 Definition) ellipsoid)|
|6018|Not specified (based on Everest 1830 Modified ellipsoid)|
|6001|Not specified (based on Airy 1830 ellipsoid)|
|6002|Not specified (based on Airy Modified 1849 ellipsoid)|
|6003|Not specified (based on Australian National Spheroid)|
|6004|Not specified (based on Bessel 1841 ellipsoid)|
|6005|Not specified (based on Bessel Modified ellipsoid)|
|6006|Not specified (based on Bessel Namibia ellipsoid)|
|6007|Not specified (based on Clarke 1858 ellipsoid)|
|6008|Not specified (based on Clarke 1866 ellipsoid)|
|6010|Not specified (based on Clarke 1880 (Benoit) ellipsoid)|
|6011|Not specified (based on Clarke 1880 (IGN) ellipsoid)|
|6012|Not specified (based on Clarke 1880 (RGS) ellipsoid)|
|6020|Not specified (based on Helmert 1906 ellipsoid)|
|6021|Not specified (based on Indonesian National Spheroid)|
|6022|Not specified (based on International 1924 ellipsoid)|
|6024|Not specified (based on Krassowsky 1940 ellipsoid)|
|6025|Not specified (based on NWL 9D ellipsoid)|
|6027|Not specified (based on Plessis 1817 ellipsoid)|
|6028|Not specified (based on Struve 1860 ellipsoid)|
|6029|Not specified (based on War Office ellipsoid)|
|6030|Not specified (based on WGS 84 ellipsoid)|
|6031|Not specified (based on GEM 10C ellipsoid)|
|6032|Not specified (based on OSU86F ellipsoid)|
|6033|Not specified (based on OSU91A ellipsoid)|
|6034|Not specified (based on Clarke 1880 ellipsoid)|
|6036|Not specified (based on GRS 1967 ellipsoid)|
|6041|Not specified (based on Average Terrestrial System 1977 ellipsoid)|
|6042|Not specified (based on Everest (1830 Definition) ellipsoid)|
|6043|Not specified (based on WGS 72 ellipsoid)|
|6044|Not specified (based on Everest 1830 (1962 Definition) ellipsoid)|
|6045|Not specified (based on Everest 1830 (1975 Definition) ellipsoid)|
|6047|Not specified (based on GRS 1980 Authalic Sphere)|
|6052|Not specified (based on Clarke 1866 Authalic Sphere)|
|6053|Not specified (based on International 1924 Authalic Sphere)|
|6054|Not specified (based on Hughes 1980 ellipsoid)|

We should fallback on one of those datum when the only information are axis lengths. It should be okay since the name makes clear that the datum is actually unknown.




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