Hi,
I write to follow up the dateline wrapping discussion (and to thank GeoSolutions for sponsoring this work).
I've just committed, only on trunk, code to perform proper processing
of projection singularities and dateline wrapping on selected projections, in particular, Mercator, Transverse Mercator, and flat
geographic.
You can see the results in the screenshots I've attached.
The 3349 is the mercator with longitude origin moved 130° away
(thus centered in the pacific ocean), 900913 is the usual Google
projection, 32632 is UTM 32N.
In all projections the geometries have been cut in a valid area
before being reprojected, in the two Mercator ones dateline wrapping
has been performed.
The classes performing the magic are here:
http://svn.osgeo.org/geotools/trunk/modules/library/render/src/main/java/org/geotools/renderer/crs/
Given we cannot rely on the CRS itself to state what is the valid
area (EPSG contains some definitions, but WKT definitions don't)
the ProjectionHandler classes assume a valid area computed from
the projection parameters, relying on knowledge of the math of
projection itself.
As you can see the ProjectionHandler is a class, not an interface.
This is because I don't know exactly how it will evolve. For one,
the class does not handle coverages, and in the future we'll
want to handle wrapping coverages as well.
Moreover the finder does not rely on SPI atm. This is because I'm
not sure we want to use SPI to start with.
What if, for example, people want to manually provide projection
handlers to have more control over them?
This is basically the reason the API is not fully fleshed out,
simply because I don't know, as of now, how a long term shape
will look like. Suggestions welcomed.
Since this is a new feature it is not enabled by default, a rendering
hint has to be provided:
rendererParams.put(StreamingRenderer.ADVANCED_PROJECTION_HANDLING_KEY, true);
This should allow backporting the changes to 2.6.x and 2.5.x without
breaking any existing code, as the new paths will lie dormant unless
explicitly activated (both backports are required in order to
get this one funded).
On GeoServer trunk I've enabled them by default to allow people to check
this functionality out.
Going forward I'd like to add projection handlers to a few more
common projections (Stereographic, Lambert), add unit tests, and
backport.
Comments?
Cheers
Andrea
--
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.
(attachments)
