Andrea Aime a écrit :
> I'm wondering if there's any way to get a validity area for a generic
> transform,
> that is, a bbox in source coordinates telling me where the transform
> works, and
> were it starts failing.
If all the following conditions are meet:
* epsg-hsql, epsg-access or epsg-postgresql is available in the classpath;
* The source and target CRS contain their EPSG code in their metadata (it
should always be the case if the CRS were created from an EPSG factory,
even if this factory was epsg-wkt);
* The "sourceCRS to targetCRS" transform is one of those that are explicitly
defined in the EPSG database (in the "Coordinate_Operation" table);
Then the "area of validity" should be defined as part of the
CoordinateOperation metadata. This area
of validity can be defined in various way, including string, geographic
bounding box, envelope or
arbitrary polygon (all this flexibility is provided by the ISO 19115 "Extent"
object). It sound like
that I didn't wrote a convenience method for extracting an envelope from a
CoordinateOperation - we
should probably open a JIRA task as a remainder that we should add such
convenience method.
In the main time, there is a convenience method for extracting an envelope or a
geographic bounding
box from a CRS. So the easier way to check the "area of validity" of a
transform is probably to invoke:
Envelope areaOfValidity = CRS.getEnvelope(operation.getTargetCRS());
Javadoc:
http://javadoc.geotools.fr/snapshot/org/geotools/referencing/CRS.html#getEnvelope(org.opengis.referencing.crs.CoordinateReferenceSystem)
Reminder: just in case you wonder what is the difference between an Envelope
(from ISO 19107) and a
GeographicBoundingBox (from ISO 19115): the Envelope can be in arbitrary CRS.
The
GeographicBoundingBox is garantee to be (longitude,latitude) in something close
to WGS84.
All the above work only for CRS or CoordinateOperation explicitly defined in
the EPSG database. If
we want a general mechanism for computing the area of validity of an unknown
coordinate operation,
this require some though. There is no such general mechanism right now in
Geotools.
Martin.
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