[postgis-devel] ST_MapAlgebraExpr(): Raster aggregates?

[Pierre Racine]

I would even suggest you write a plpgsql prototype for ST_UnionToRaster() based on the specifications.... ...if you have time for sure.

I would be glad to add it in the plpgsql/script on the trunk. It then becomes the reference for a future C implementation.

Pierre

> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net [mailto:postgis-devel-
> bounces at postgis.refractions.net] On Behalf Of Pierre Racine
> Sent: Friday, November 18, 2011 10:39 AM
> To: PostGIS Development Discussion
> Subject: Re: [postgis-devel] ST_MapAlgebraExpr(): Raster aggregates?
> 
> Tom,
> 
> Look at the plpgsql prototype of ST_Union(raster) in
> 
> http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_union.sql
> 
> Have a look also at the specifications of ST_UnionToRaster(geometry, val) in
> 
> http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03
> 
> Everything is based on ST_MapAlgebraExpr(raster, raster, expr) and should do
> exactly what you want.
> 
> It should be ok for producing low resolution raster as our first implementation of
> ST_MapAlgebraExpr(raster, raster) process pixel by pixel. Higher resolution will
> need an optimized version of ST_MapAlgebra(raster, raster) copying large areas
> of raster values when possible (it is exactly what we need for unioning two
> rasters efficiently). We started to make a plpgsql prototype for this optimized
> version but it is not finished
> (http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql/st_mapalge
> bra_optimized.sql). I guess we will need some funding to make it happen...
> 
> Let me know about your experiments...
> 
> Pierre
> 
> 
> > -----Original Message-----
> > From: postgis-devel-bounces at postgis.refractions.net
> > [mailto:postgis-devel- bounces at postgis.refractions.net] On Behalf Of
> > Tom van Tilburg
> > Sent: Friday, November 18, 2011 6:25 AM
> > To: postgis-devel at postgis.refractions.net
> > Subject: [postgis-devel] ST_MapAlgebraExpr(): Raster aggregates?
> >
> > Hi list,
> >
> > At the moment I'm looking at the option of turning vector maps with
> > discrete (non overlapping)  data into rasters with the help of the WKTraster
> functionality.
> > At the moment I do as follows:
> > 1. Collect (aggregate) al geoms from the same class 2. Make the into a
> > raster with St_AsRaster() 3. Repeat for all classes 4. Merge all
> > resulting rasters into 1 with ST_MapAlgebraExp()
> >
> > This step 4 I have to repeat (nest) a lot of times (for every class I
> > have in my vector data). It would be great to have St_MapAlgebraExp()
> > as an  aggregate function instead of just 2 rasters. This would
> > greatly simplify the process of turning land use data from
> > vectors/topology into raster. Is there any such thing available or in the make?
> >
> > Regards,
> >   Tom
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