[postgis-users] Querying Multiple Rasters

Tue Jul 30 09:12:27 PDT 2013

Jayson,

Can you share one of the queries? Also, what check constraints are you
using?

-bborie

On Tue, Jul 30, 2013 at 7:49 AM, Jayson Gallardo <jaysontrades at gmail.com>wrote:

> So, I used Explain on my SELECT statement, and whether
> constraint_exclusion is on or off, it seems to spit out the same number of
> rows in the query plan. Is there something I need to do for my table
> constraints so that it doesn't do a check on every table I have loaded?
>
>
> On Tue, Jul 30, 2013 at 9:20 AM, Jayson Gallardo <jaysontrades at gmail.com>wrote:
>
>> Quick follow up question to my situation... I recently loaded 3m
>> resolution NED for Iowa. I have them loaded to one table per source tile,
>> and have them inheriting from the parent table that the Arkansas NED is
>> inheriting from. Ever since, however, my database seems to be running
>> pretty slow. I've run a full vacuum on the data, and there are constraints
>> on each table.
>>
>> How can I be sure that when I query the parent database that it's not
>> querying every single table?
>>
>>
>> On Tue, Jul 23, 2013 at 3:14 PM, Bborie Park <dustymugs at gmail.com> wrote:
>>
>>> I'm just glad to help. Feel free to post your experience, feedback,
>>> issues and/or wishes on the mailing-list.
>>>
>>> -bborie
>>>
>>>
>>> On Tue, Jul 23, 2013 at 1:10 PM, Jayson Gallardo <jaysontrades at gmail.com
>>> > wrote:
>>>
>>>> Oh, okay. Yeah you're right about it taking time. I wrote a python
>>>> script to generate the raster2pgsql call with the appropriate table name,
>>>> so I can just let it run while I do other things. I really appreciate your
>>>> help on this. I googled your name and I see you're a pretty busy person, so
>>>> I'm glad you're taking the time to answer my questions.
>>>>
>>>>
>>>> On Tue, Jul 23, 2013 at 3:05 PM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>
>>>>> No. I'm suggesting it later as it does take time and separates
>>>>> operations. Get everything imported first and then add constraints.
>>>>>
>>>>> Having said that, you can do it all at once if so desired... just
>>>>> preference depending on volume of import data.
>>>>>
>>>>> -bborie
>>>>>
>>>>>
>>>>> On Tue, Jul 23, 2013 at 1:02 PM, Jayson Gallardo <
>>>>> jaysontrades at gmail.com> wrote:
>>>>>
>>>>>> Okay, is there a specific reason why? As your link states: "
>>>>>> raster2pgsql loader uses this function to register raster tables".
>>>>>> Are you saying I should specify constraints that will be similar across all
>>>>>> tables?
>>>>>>
>>>>>>
>>>>>> On Tue, Jul 23, 2013 at 2:53 PM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>>>
>>>>>>> I'd suggest adding constraints after the fact through SQL instead of
>>>>>>> letting raster2pgsql do it.
>>>>>>>
>>>>>>> http://www.postgis.net/docs/manual-2.0/RT_AddRasterConstraints.html
>>>>>>>
>>>>>>> -bborie
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Jul 23, 2013 at 12:51 PM, Jayson Gallardo <
>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>
>>>>>>>> So based on the link you provided, and what else I've gathered, I
>>>>>>>> first create a parent table:
>>>>>>>>  CREATE TABLE dem_elevation
>>>>>>>> (
>>>>>>>>   rid integer NOT NULL PRIMARY KEY
>>>>>>>>   rast raster,
>>>>>>>>
>>>>>>>> );
>>>>>>>>  Then I run raster2pgsql on all the downloaded elevation data,
>>>>>>>> sending each input tile to its own table, ie. dem_elevation_n36w091. Then
>>>>>>>> alter table to inherit from parent:
>>>>>>>> ALTER TABLE dem_elevation_n36w091 INHERIT dem_elevation;
>>>>>>>>
>>>>>>>> With raster2pgsql taking care of setting the constraints for each
>>>>>>>> table. Now, I can just query the parent table dem_elevation to get what I
>>>>>>>> need?
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Jul 23, 2013 at 2:33 PM, Bborie Park <dustymugs at gmail.com>wrote:
>>>>>>>>
>>>>>>>>> I use the USGS NED 10 meter for California with one table for each
>>>>>>>>> input raster. In the partitioned table scheme, data tables inherit from a
>>>>>>>>> template (parent) table. Queries run on the parent table access the
>>>>>>>>> inherited tables.
>>>>>>>>>
>>>>>>>>> -bborie
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Tue, Jul 23, 2013 at 11:56 AM, Jayson Gallardo <
>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> Yes, it's usgs ned. And I initially went with one table for each
>>>>>>>>>> input tile, but I didn't know how to join (or union) them together for my
>>>>>>>>>> query.
>>>>>>>>>>  On Jul 23, 2013 1:14 PM, "Bborie Park" <dustymugs at gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> Can you describe your elevation dataset? Is it USGS NED? At
>>>>>>>>>>> which resolution (10 meter, 3 meter?)?
>>>>>>>>>>>
>>>>>>>>>>> As for table partitioning...
>>>>>>>>>>>
>>>>>>>>>>> http://www.postgresql.org/docs/9.0/static/ddl-partitioning.html
>>>>>>>>>>>
>>>>>>>>>>> You'll probably partition spatially, though an easy solution is
>>>>>>>>>>> to have a table for each input raster file.
>>>>>>>>>>>
>>>>>>>>>>> -bborie
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Tue, Jul 23, 2013 at 11:05 AM, Jayson Gallardo <
>>>>>>>>>>> jaysontrades at gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Thanks for responding. Could you outline how I would go about
>>>>>>>>>>>> doing a partitioned table structure? My only concern with tile size is
>>>>>>>>>>>> processing time. Most of my queries will involve areas of less than 1 mi^2,
>>>>>>>>>>>> and I would clip the data into that shape. I just don't know where to
>>>>>>>>>>>> start! There's not too many resources online/print dealing with postgis
>>>>>>>>>>>> rasters in detail.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Jul 23, 2013 at 12:57 PM, Bborie Park <
>>>>>>>>>>>> dustymugs at gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> 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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