[OpenLayers-Dev] projection on geometry

Tim Schaub tschaub at opengeo.org
Tue Nov 11 16:47:49 EST 2008


Picking up on the thread that Bart just referenced:

I agree, we should keep track of projection at the geometry level.

There are plenty of times that you have a geometry without a feature or 
a layer, and you want to maintain the srs info for that geometry.

I've always thought this change would come with 3.0.  But it probably 
makes sense to start working it in to see how things go.

Seems to me like we need a setter and getter.  So the following would work:

polygon.components[0].components[0].getProjection(); // foo

And it makes sense to me to push the work on to the setter (setting the 
same on all components), making access less work.

I think it also makes sense to me that the layer does not set the 
geometry projection.  We assume that geometry projection is properly set 
before a feature is added to a layer.  This pushes the setting or 
transforming closer to the parsing (where it makes sense that you'd know 
the projection).

In some cases, a format would do the transform (assuming 
internal/externalProjection are set).  In other cases, a strategy could 
do the transform (since it knows the map projection and the layer 
projection - where the layer projection should be set to match the source).

I'm sure there's lots more to talk about.  This is what a sprint is good 
for.  Without that, it probably makes sense to get some code going and 
see where it takes us.  To this end, I've created a new sandbox [1].  I 
won't have any time for a bit to work on it, but I'll be happy to comment.


[1] http://svn.openlayers.org/sandbox/projection

Tim Schaub
OpenGeo - http://opengeo.org
Expert service straight from the developers.

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