[postgis-devel] Another idea to speedup raster value editing

[Pierre Racine]

The plan was to be able to provide an array and a X and a Y shift to know where to write the values from the array if the number of value provided is less than the actual number of pixels.

So SetValues(rast, ARRAY[1,2,3])  would edit the first three pixels and SetValues(rast, ARRAY[1,2,3], 2, 3)   would edit the second, third and fourth pixels of the third row.

If the values you want to edit are a function of the existing values (or the values of another raster) and you want to edit all of them, use ST_MapAlgebra. 

If the values are not a function of the existing values use ST_SetValues.

Pierre

> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net [mailto:postgis-devel-
> bounces at postgis.refractions.net] On Behalf Of Paul Ramsey
> Sent: Wednesday, February 01, 2012 10:28 AM
> To: PostGIS Development Discussion
> Subject: Re: [postgis-devel] Another idea to speedup raster value editing
> 
> Kinda... but then you've got a multipoint to deal with and that's easier
> because...?
> How about just getting/taking an array?
> P.
> 
> On Wed, Feb 1, 2012 at 12:52 AM, Sandro Santilli <strk at keybit.net> wrote:
> > I've been thinking that for my use case (create the NTv2 gridshift) it
> > would be fast to pass a measured MULTIPOINT geometry where X/Y would
> > address the pixel and M would set the value.
> >
> > The same representation could be useful in output, to use in place of
> > ST_PixelAsPolygon.
> >
> > Such function, implemented in C, would allow to set and get all values
> > in a band with a single raster deserialization.
> >
> > Map algebra, btw, you could perform on the M values directly.
> > Something like:
> >
> >  WITH
> >  pixels AS (
> >    SELECT (ST_DumpPixelsAsPointM(rast)).geom FROM myrasttable
> >  ),
> >  newpixels AS (
> >    SELECT ST_Point(ST_X(geom),ST_Y(geom), ST_M(geom)+1) as geom
> >  )
> >  SELECT ST_SetValueFromPointM(rast, st_collect(geom) FROM newpixels;
> >
> > How do you like it ?
> >
> > --strk;
> >
> >  ,------o-.
> >  |   __/  |    Thank you for PostGIS-2.0 Topology !
> >  |  / 2.0 |    http://www.pledgebank.com/postgistopology
> >  `-o------'
> >
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