[postgis-users] Retrieving Data from PostGIS Raster using ST_Value

Nordgren, Bryce bnordgren at fs.fed.us
Wed Oct 12 13:01:48 PDT 2011

1.44 million pixel accesses does not sound like something that should take 1/2 hour.  

For better or worse, raster depends on Postgresql's underlying caching mechanism to make data I/O efficient; and the unit of caching is one "raster tile". If I read the SRTM3 data description correctly, each pixel is a 16 bit int, making for a 2.88 Mb "raster tile" (if you loaded it all into one row.) I'm a little out of my depth here, but your tile may be too big for postgresql to cache.  Does performance improve if you load the SRTM data into many raster tiles?  


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of elliott
Sent: Wednesday, October 12, 2011 8:28 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Retrieving Data from PostGIS Raster using ST_Value

It is just one SRTM3 tile which is 1201 x 1201.  The data is used by scientific codes to determine the elevation at a given latitude and longitude.

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