[postgis-users] ST_SelectByValue

[Pierre Racine]

If you set the values you're looking for to themselves and other pixels to nodata, ST_Reclass is equivalent to ST_SelectByValue.

> -----Original Message-----
> From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-
> bounces at lists.osgeo.org] On Behalf Of David Haynes
> Sent: Thursday, June 05, 2014 3:34 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] ST_SelectByValue
> 
> reclass would allow me to change the values of the pixel.
> 
> "ST_SelectByValue" is supposed to like a map algebra or in ArcGIS Terms
> select by attribute.
> 
> 
> On Thu, Jun 5, 2014 at 1:38 PM, Pierre Racine
> <Pierre.Racine at sbf.ulaval.ca> wrote:
> 
> 
> 	Try ST_Reclass().
> 
> 
> 	> -----Original Message-----
> 	> From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-
> users-
> 	> bounces at lists.osgeo.org] On Behalf Of David Haynes
> 	> Sent: Friday, May 30, 2014 10:49 AM
> 	> To: postgis-users at lists.osgeo.org
> 	> Subject: [postgis-users] ST_SelectByValue
> 	>
> 	> Hello,
> 	>
> 	> I am fairly new to using rasters in postgis, but I am wondering if
> there is a
> 	> faster way to extract values from categorical rasters (e.g.
> landcover types)
> 	> than using map algebra. In the PostGIS in Action book, pg 404 has
> a
> 	> function called ST_SelectByValue(raster|geometry, 'expression')
> which
> 	> seems to incorporate map algebra, however I can't seem to tell if
> this
> 	> function is finished and available in postgis as I get an unknown
> function
> 	> error.
> 	>
> 	> My version is this.
> 	> "PostgreSQL 9.3.2 on x86_64-unknown-linux-gnu, compiled by gcc
> 	> (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit POSTGIS="2.1.1
> r12113"
> 	> GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.7.1, 23 September 2009"
> 	> GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8"
> LIBJSON="UN
> 	> (...)"
> 	>
> 	>
> 	> And I found a webpage
> 	>
> http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03
> 	>
> 	> search for "ST_SelectByValue" at the bottom, indicating that it
> was finished.
> 	>
> 	>
> 	> AAccomplished Objectives
> 
> 	>
> <http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking03#A
> 	> ccomplishedObjectives>
> 
> 	>
> 	>
> 	> ST_ValueCount(raster, value) -> integer - done see below
> 	>
> 	> ST_ValuePercent(raster, value) -> double precision - done see
> below
> 	>
> 	> ST_Resample(raster, method, originx, originy, pixelsizex,
> pixelsizey) -> raster
> 	> - done see below
> 	>
> 	> ST_SelectByValue(raster, 'expression') -> same type as first
> argument
> 	>
> 	> ST_Clip(raster|geometry,geometry) -> same type as first
> argument
> 
> 
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