[postgis-users] may have postgis store limits for a big project?

[Pierre Racine]

>We do not know yet.. it could be even hundreds !

WKT Raster is not really limited in size. But we still have to test on datasets the size you are using.

>each region (european country, US state, province, etc...) would have few raster (even 20) >representing different kind of information... (each pixel would be 5mx5rm)...

With WKT Raster, you can store all those rasters as a unique tiled coverage. In Oracle probably you stored them one table per raster?

>and I need to know the value of a pixel for all the rasters in that particular coordinates...

For this you typically use ST_Value() like this:

SELECT ST_Value(rast, ST_Geomfromtext('Point(-78.1 58.1)', 4326))
FROM srtm_tiled_100x100
WHERE ST_Intersects(rast::geometry, ST_Geomfromtext('Point(-78.1 58.1)', 4326))

One query like this takes 16 milliseconds on my machine on a 100 pixels x 100 pixels tiled coverage. There are 46800 tiles.

Don't forget to assign a reference system to your raster when converting it to .sql (-s gdal2wktraster's option) and to construct an index on the table (-I option).

>with Oracle 11g GEORaster it is possible to compress the rasters (and get lower performance of >course)... in my case the compression rate is up to 600 !!!... so the amount of data is >drastically reduced...

WKT Raster relies on PostgreSQL for compression. I don't know the compression rate.

>nevertheless I need to be able to do a few (up to 20) queries like this at the same time in in a >fraction of second...: select pixel from raster where (x=X and y=Y). One query for each raster, >representing a different information

If you tile and index everything properly that should not be a big deal. Let us know!

>If WKTRaster is mature enough, we can create a cluster without the need of paying a prohibitive license per CPU as for Oracle !

If you save extra money by not having buying an Oracle license and you are interested in collaborating in the development of WKT Raster, let us know ;-)

Pierre

Sebastian
On Mon, Jul 19, 2010 at 5:00 PM, Pierre Racine <Pierre.Racine at sbf.ulaval.ca> wrote:
Hi Sebastian,

What kind of query are you planning on the raster? You know you can also use WKT Raster to simply "register" filesystem rasters, creating a king of geospatial catalog, without actually storing them in the database...

How many 16GB raster do you have? Are your raster all representing the same theme? Are they overlapping (or they form a regular grid)?

We don't know of that many users cases up to now, but WKT Raster prooved to be very stable working on 1 GB raster coverage (see the tutorial).

Pierre

From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Sebastian E. Ovide
Sent: 19 juillet 2010 11:34
To: PostGIS Users Discussion
Subject: Re: [postgis-users] may have postgis store limits for a big project?

Hi All,

I am interesting too... I am considering PostGIS+WKTRaster instead of Oracle GeoRaster... but for that can happen, Postgresql must be able of managing some simple tables of 30+M (Millions) rows plus a lot of Rasters of 16GB each... (16GB not compress data... so are huge images !). Each query (simple look up) must response in a fraction of second....

any successful case ?

Thanks !
On Fri, Jul 16, 2010 at 1:13 AM, salas <fsalas at geocuba.cu> wrote:
Hello to all:
I am working in a project where they are managed more than 20 geoespatials thematics. Each thematic one has a considerable volume of since information it is of the whole country (I am speaking of a lot more than a million of records). In the project we need to make (mostly) intersection consultations keeping in mind literal attributes.
I need to know the experience of somebody in a project of this span and if PostGIS would present some limitation therewith.

regards yuriesky

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