[postgis-users] WKTraster pixel value

[Pierre Racine]

You don't need the function ST_Band...

You need to be able to do something like:

SELECT ST_Max(r),  ST_Min(r) FROM ST_Clip(raster, mypolygon)) r

ST_Clip() is planned but  ST_Min() and ST_Max() are not but should definitely be welcome.

Pierre


From: Rainer Zaiss [mailto:Rainer.Zaiss at ird.fr]
Sent: 9 février 2010 08:54
To: Pierre Racine
Subject: RE: [postgis-users] WKTraster pixel value

Hi Pierre,

Thank you very much for your reply. I just want to calculate the Min and Max value of my raster inside an area of interest. The raster file is a DEM single band raster the area of interest is a polygon. I guess I need the function  ST_Band(raster, band)). I will wait I while until the function will be implemented.

Thank you

Rainer Zaiss
Secteur Cartographie
IRD - Centre de recherche d'Île-de-France
32, avenue Henri Varagnat
93143 Bondy cedex
Tél: 01 48 02 55 06
Fax: 01 48 02 79 35
Rainer.Zaiss at ird.fr<mailto:RaRainer.Zaiss at ird.fr>
http://www.bondy.ird.fr/carto
________________________________
De : Pierre Racine [mailto:Pierre.Racine at sbf.ulaval.ca]
Envoyé : mardi 9 février 2010 14:19
À : Rainer.Zaiss at ird.fr; PostGIS Users Discussion
Objet : RE: [postgis-users] WKTraster pixel value

Rainer,

There is a difference between accessing a whole band of a multiband raster and access a single pixel value.

The ST_Band(rast raster, band integer) function (not yet implemented) will return a whole band (i.e. an object of type raster).

The ST_Value(rast raster, band integer, x integer, y integer) function (implemented but not yet documented) returns the value of a single pixel expressed as a float point value.

Pierre

From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Rainer Zaiss
Sent: 9 février 2010 04:10
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] WKTraster pixel value

Dear list,

I just played around with WKTraster. I just want to have a confirmation that the function to access the pixel values is not yet implied (ST_Band(raster, band)) ?

Thank you very much for your help

Rainer


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