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

[Nordgren, Bryce]

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?  

Bryce


-----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.