Robin,
I can't say for certain but it looks like your client (not psql) is
sending off multiple queries. The nulls would return if the point being
sampled isn't in any of the tiles.
You could enable statement logging (log_statement) in PostgreSQL to see
what statements are being run from your connector.
http://www.postgresql.org/docs/9.0/interactive/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHAT
-bborie
On 06/29/2012 09:51 AM, Robin Wilson wrote:
> Hi,
>
> I'm fairly new to PostGIS and PostGIS raster stuff, so this may be a really
> simple question - hopefully someone will be able to help me anyway.
>
> I am running the following SQL statement:
>
> SELECT ST_Value(rast, ST_PointFromText('POINT(-59 -1)', 4326)) FROM modis.test
>
> In this case, rast is the raster column in the table modis.test, which has a
> tiled raster dataset in it. When I run this query through psql I get a single
> result (4993), but when I run it through the Postgres adaptor in the
> programming language I'm using (node.js in this case) I get lots and lots of
> null results, with the one real value (4993) in the middle of them, with one
> row for each tile of the data.
>
> [ { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: null },
> { st_value: 4993 },
> { st_value: null },
> { st_value: null } ]
>
> Is there a way to stop this happening? I have tried adding a "WHERE st_value
> IS NOT NULL" but that doesn't seem to give any results at all. Is there a way
> of getting the SQL statement to treat the raster dataset like GDAL does with
> mode = 2 - ie. a table as one whole tiled raster not individual rasters?
>
> Cheers,
>
> Robin
> PhD Student
> University of Southampton
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--
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
bkp...@ucdavis.edu
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