[postgis-users] ST_Value

[Pierre Racine]

>  I tried to extract the elavation value of a particular location on the SRTM data i
> loaded on my database using the following command SELECT
> ST_Value(rast,ST_Point(-106.2,38.6)) AS Elevation  From srtm;
> 
> but it only brought out a long  elevation column with no value shown.
> What could be the issue?

You have to assign a SRID to your point with ST_SetSRID(). If this SRID is not the same as the raster you must then reproject your point using ST_Transform().

> Also If i try to issue a command like this :
> 
> SELECT ST_Value(rast) AS Elevation
>  From srtm
>  Where rid = 1304;
> 
> Error message. "function st_value(raster) does not exist"

ST_Value is for extracting one value from a raster. What you wrote makes no sense since you are not saying which one to extract... You must specify the x and y of the pixel for which you want a value or pass a geometry point (in the same SRID).

Pierre