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

[Tom van Tilburg]

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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