[postgis-users] Unable to build WKT Raster

[Pierre Racine]

Gilles,

Glad you could build WKT Raster and it's working fine.

In order "to extract cells having "value > n" and build a polygon from those" you would need ST_SelectByValue(raster, ‘expression’) which would return a raster containing only the selected pixels (the others being filled with NODATA values) and then ST_AsPolygon(raster) which will convert every group of contiguous pixel with same value to a polygon.

These two functions are planned but unfortunately not implemented yet. If you can give a hand you are welcome. ST_AsPolygon(raster) is planned to be implemented very soon but not ST_SelectByValue(raster, ‘expression’).

Pierre

>-----Original Message-----
>From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
>bounces at postgis.refractions.net] On Behalf Of Gilles Bassière
>Sent: 2 novembre 2009 18:34
>To: PostGIS Users Discussion
>Subject: Re: [postgis-users] Unable to build WKT Raster
>
>Mateusz Loskot wrote:
>> The WKT Raster README file available from
>> http://trac.osgeo.org/postgis/browser/spike/wktraster/README
>> says
>>
>> "latest 1.3.5 release won't work"
>>
>
>I've seen this indeed but was confused by other sources of documentation.
>
>In the meantime, I've managed to build PostGIS 1.4 and WKT raster
>against it. It seems to work fine except that "make install" try to copy
>gdal2wktraster.py directly to postgresql bin dir, ignoring the custom
>prefix. Anyway, I copied the file manually and wktraster is now all set up.
>
>I've been able to load an SRTM tile and fetch individual values using
>st_value. What I'd like to do is to extract cells having "value > n" and
>build a polygon from those. Is this the kind of query wkt raster is
>intended to support?
>
>Regards
>
>--
>Gilles Bassière - MAKINA CORPUS
>http://www.makina-corpus.com
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