[postgis-users] Querying Multiple Rasters

[Bborie Park]

You may not need to drop all the constraints when adding additional data to
the table. You most likely will need to drop is the maximum extent
constraint. Assuming the input rasters have the same scale, skew and SRID
as that found in the table, you don't need to drop those corresponding
constraints.

If you're going to do the continental US at a fine resolution (e.g. 1
meter), you do NOT want to put all the rasters in one table. You'll want to
use a partitioned table structure and should consider a bigger tile size
(depending on your hardware).

-bborie


On Tue, Jul 23, 2013 at 10:43 AM, Jayson Gallardo <jaysontrades at gmail.com>wrote:

> I've looked and looked, but I have not been able to find an answer to my
> question. I have downloaded elevation data for the state of Arkansas (in
> the form of multiple tiles), and used raster2pgsql to upload it into a
> single table:
>
> raster2pgsql -I -C -e -F -t 50x50 -l 2,4 n*/grdn* public.dem_elevation |
> psql -U postgres -d testdb -h localhost -p 5432
>
> I did this because I didn't know how to pull the data if they were in
> separate tables. Now, however I would like to add elevation data for other
> areas. I tried to just add it to the current table, but that required
> dropping the constraints which for such a huge amount of data seems to take
> a long time (I let it run for 24+ hours and it didn't finish). So, my
> question is, if I load all my rasters as individual tables, how could I run
> something similar to this query on them all (from a python script):
>
> SELECT ST_AsGDALRaster(ST_CLIP(ST_Union(rast),
> ST_GeomFromText(WKT,900913)),'GTiff') FROM "dem_elevation" WHERE
> ST_Intersects(rast, ST_Transform(ST_GeomFromText(WKT,900913),4269))
>
> My goal, if it's not obvious, is to clip elevation data and export it to a
> GTiff format and perform some operations on that raster data. Eventually, I
> would like to put the whole continental US elevation data into my database,
> so I need to be able to do so, while still being able to query them based
> on an area of interest the user selects from a map. I started working with
> PostGIS and Mapserver last month, so please forgive my ignorance on such
> topics. Thanks in advance
>
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