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

[Pierre Racine]

Thanks for this feedback Tom.

Could you tell us more on 1) What you do exactly? 2) The characteristics of your dataset (size, pixeltype) and the performance of ST_Union?

You are the first on earth one to do raster aggregation of real rasters in a spatial database!

I developed and tested ST_Union only on 100x100 rasters...

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: Wednesday, November 23, 2011 8:54 AM
> To: postgis-devel at postgis.refractions.net
> Subject: Re: [postgis-devel] ST_MapAlgebraExpr(): Raster aggregates?
> 
> Tested and working as expected.
> This is a very usefull addition. Thanks for the effort all!
> 
> Tom
> 
> 
> On 21-11-2011 22:28, Pierre Racine wrote:
> > Tom,
> >
> > ST_Union is.... Fixed! Thanks to Bborie.
> >
> > Just update your source, create a fresh database (or get rid of the
> > old MapAlgebra4Union) and execute everything up to the tests at the
> > bottom of the file. Have a visual look at the test using OpenJump or
> > QGIS (they were written for OpenJump with the ST_Asbinary() converting
> > the vectorization of the result.)
> >
> > Let us know about your tests.
> >
> > For those who might be interested ST_Union() is the prototype of a
> > function aggregating overlapping rasters into a single raster. It does
> > pretty much the same thing as the ST_Union(geometry) aggregate but for
> > rasters. Since it is an AGGREGATE you can use GROUP BY to aggregate
> > based on the value of a column. You have to specify how you want
> > raster values to be aggregated. I implemented shortcuts to MAX, FIRST,
> > LAST, COUNT, SUM, RANGE and MEAN, but you can define your own
> complex
> > aggregator by defining a STATE expression, a TEMPORARY and a FINAL
> > expression. Have a look at the specifications in
> >
> > http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03
> >
> > And have fun!
> >
> > 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: Monday, November 21, 2011 5:05 AM
> >> To: PostGIS Development Discussion
> >> Subject: Re: [postgis-devel] ST_MapAlgebraExpr(): Raster aggregates?
> >>
> >> Pierre,
> >>
> >> Thanks a lot for pointing me out this.
> >> I've looked in to the plpgsql code but I'm afraid my current
> >> knowledge (or time) doesn't allow me to contribute code.
> >>
> >> However, I tested the prototype of ST_Union. It appears to be rather
> >> buggy (typo's). Has it ever been applied/tested?
> >> (eg: 'ERROR:  parameter name "p_nodata1expr" used more than once. '
> >> seems to be copy paste error.)
> >>
> >> Chrs,
> >>    Tom
> >>
> >> On 18-11-2011 16:54, Pierre Racine wrote:
> >>> 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
> >>>> /s t_mapalge bra_optimized.sql). I guess we will need some funding
> >>>> to make it happen...
> >>>>
> >>>> Let me know about your experiments...
> >>>>
> >>>> Pierre
> >>>>
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