On Fri, Aug 15, 2014 at 10:24 AM, Andrea Aime <andrea.a...@geo-solutions.it> wrote:
> > What you are doing here in GeoTools is a rendering/store hint called > ScreenMap, and it's normally applied in memory. > However, theoretically we could do the same as, say, MinVisitor, and have > the store use a native and faster > implementation of it, like JDBCDataStore does (turning it into a select > min). > > To make it possible we'd need to have ScreenMap provide its internal > information I supposed, the rendering rectangle, > and the grid to world transformation. > > The advantage of doing so would be that your users would not have to add a > rendering transformation in the SLD, > it would just work automatically (downsize, there would be no way to turn > it off). > > Cheers > Andrea > > So essentially using the ScreenMap information as a way to pass down the grid <-> world transform function information to a place where pushdown support on a datastore can be implemented. That definitely fits in a little more smoothly than requiring the WPS in the SLD (as you mention). The inability to turn it off (which you also highlight) would be my concern. To make it more "fire and forget" I think the distributed rendering option I talked about would be required. (To deal with symbolizers in grid space that aren't equivalent to the native geometry in that same grid space). There's the efficiency optimization if the symbolizer is larger than the geometry - but the bigger concern is the "incorrectness" if the symbolizer is smaller than the geometry. For points that's not really a huge issue (only case I think it would break would be with offsets). But for lines and polygons it's a definite issues. For the distributed rendering portion this is definitely something I want to dig in to. I saw your latest commit, and this seems to be like a good pointer into digging into this (ScreenMap) functionality: https://github.com/geoserver/geoserver/commit/b64b03f7e5f02ddddb090d8ff45c0a75cd823e20 Thanks! (for the idea, and for the unrelated but fortuitous fix)
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