Bursa-Wolf parameters selection in the EPSG database
----------------------------------------------------
Key: GEOT-1179
URL: http://jira.codehaus.org/browse/GEOT-1179
Project: GeoTools
Issue Type: Bug
Components: core referencing
Affects Versions: 2.3.0, 2.4.M0
Reporter: Martin Desruisseaux
Assigned To: Martin Desruisseaux
Fix For: 2.4.0
Geotools currently try to select Bursa-Wolf parameters from the EPSG database
using the following algorithm:
{panel}
For a given _source_ and _target_ datum pair, we pickup the first set of
parameters returned by a SQL statement that contains the following clause:
{noformat}
ORDER BY ABS(DEPRECATED), COORD_OP_ACCURACY, COORD_OP_CODE DESC
{noformat}
So deprecated parameters are last. If there is more than one non-deprecated set
of parameters, the most accurate one is selected. If they all have the same
accuracy, we choose the one with the highest primary key value, assuming that
it is the most recently added. I admit that this last rule is not a very
reliable one, but in the particular case of EPSG:4289, it seems to work.
{panel}
However this algorithm lead to the selection of the following parameters for
EPSG:4312 ("MGI"):
{noformat}
TOWGS84[426.9, 142.6, 460.1, 4.91, 4.49, -12.42, 3.5271281868253483]
{noformat}
This seem to be the values for Slovenia. The expected values should be:
{noformat}
TOWGS84[577.326, 90.129, 463.919, 5.1365988, 1.4742, 5.2970436, 2.4232]
{noformat}
This is in EPSG 6.12, Coordinate Transformation 1618: MGI to WGS 84 (3). The
same issue apply to all projected CRS derived from the 4312 geographic CRS,
like EPSG:31286
We need to improve the way Geotools selects the set of Bursa-Wolf parameters.
Just looking at the source and target datum is not suffisient.
We also need a mechanism that warn the user when more than one set of
Bursa-Wolf parameters were found for a given geographic CRS, so the user know
that the set selected by Geotools may not be the most appropriate one. We also
need a mechanism for forcing the selection of a particular set of Bursa-Wolf
parameters, to override the automatic selection.
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