[postgis-users] PostGIS Raster Performance

Mon Jan 31 08:14:00 PST 2011

Just to mention that I did try the gdal driver for PGRaster and it is
working. I can't tell the speed, and like mentionnend Simon it depends of
many things. But I did succeed to render (query and write to disk as an
ascii file with prj file) a 100x100 pixels 32b float, single band using
gdal_translate in the latest release version.

Etienne

On Mon, Jan 31, 2011 at 10:46 AM, Pierre Racine <Pierre.Racine at sbf.ulaval.ca
> wrote:

> Sunny,
>
>
>
> There are two planned options for serving raster from PostGIS raster:
>
>
>
> The first (1) is to just register the raster as out-of db raster. Only the
> georeferences of each tile/raster is stored in the database along with the
> path to the raster itself in the filesystem (you can add any other attribute
> as additional columns). PostGIS raster in this case act like a quick SQL
> raster catalog. Actual raster data (pixel values) are not stored in the
> database. They are store as JPEG or TIFF in the filesystem. It is up to the
> application to fetch them where they are. In this case their should be no
> performance lost comparing with any existing raster server solution storing
> raster coverage in the filesystem. This options still need
> testing/improvement. For example, the loader (raster2pgsql.py) is not able,
> right now, to split big raster into multiple JPEG tiles when you use the –k
> option. It does it only when you store the tiles in-db.
>
>
>
> The second (2) option is to store everything in the DB. The raster is then
> stored in the PostGIS raster format and need to be converted to JPEG before
> being sent to web client (desktop applications do not have to rely on this
> conversion as can implement native support for the PostGIS raster WKB format
> or rely on GDAL). There are two ways to convert PostGIS raster to JPEG or
> whatever: the first one (2.1) is to rely on the PostGIS raster GDAL driver
> used by the application (this is how we got almost free support in
> MapServer). The second one (2.2) is to ask the database to convert PostGIS
> rasters to JPEG or whatever format with SQL functions like ST_AsJPEG(rast)
> or ST_AsTIFF(rast) so that the application receive a JPEG or TIFF binary
> stream. These function are planned but not yet implemented. This option
> should be a bit slower than the first as raster are converted on the fly.
>
>
>
> Option (1), storing out-of-db, targets applications needing VERY faster
> retrieval not requering raster edit or analysis and not implemented to read
> native PostGIS or GDAL raster.
>
>
>
> Option (2), in-db storage, targets applications needing raster edit or
> analysis and able to read native PostGIS or GDAL raster.
>
>
>
> Options 1 and 2.2 assume that raster tiles can be sent to the web
> application without having to be blended with other layers. Application
> (like MapServer) that has to read and blend rasters with other layers before
> sending them should rely on 2.1 (GDAL). I think this last option has the
> better future. It is however not very well tested right now and the GDAL
> driver just got reimplemented in december. We might have to tweak it at some
> point to get the kind of performance expected by web applications.
>
>
>
> I suggest you give a try to MapServer (Regina & Leo explain how to
> configure it in PostGIS in Action) and, if it is not fast enough, see with
> Jorge what we can do.
>
>
>
> To answer your other questions: raster loading in PostGIS raster is quite
> fast even if it still need improvement like not passing through a large
> intermediate SQL file.
>
>
>
> Could you elaborate a bit more on the multiband issue? I’m not very
> familiar with tile caching tech anymore.
>
>
>
> Pierre
>
>
>
>
>
> *From:* postgis-users-bounces at postgis.refractions.net [mailto:
> postgis-users-bounces at postgis.refractions.net] *On Behalf Of *Sunny Teo
> *Sent:* 29 janvier 2011 21:25
> *To:* PostGIS Users Discussion
> *Subject:* Re: [postgis-users] PostGIS Raster Performance
>
>
>
> Hi Regina,
>
>
>
> Thanks for the lead on this.
>
>
>
> It opens up the light and the room for discussion. Well, as far as I know,
> Oracle Georaster is not good for serving purpose and on top of it, that
> takes awful amount of time to load the data into Oracle. I assume that its
> not the case with PG Raster.
>
>
>
> The other issue is, even if one dont want to do store the multiband (say 8
> band) imagery into the PG Raster for the Speed issue, can we target to link
> up the Cache into this? If GWC or Tile Cache jpg/png tiles can be kept here
> and then publish... it will be nice. Again, the issue will be speed ... or
> some may argue the fact the it defeats the purpose of Cache which is suppose
> to be non "ram" required serving.
>
>
>
> my only wish, that one day we should be able to easily load the images into
> PG Raster and publish into a web application and get a performance/speed as
> good as any image servers.
>
>
>
> btw, it was a news to me that GeoServer dont support PG Raster yet... I
> hope they are working on it now...
>
>
>
>
>
> Thank you;
>
> Sunny
>
>
>
>
>
> On Sun, Jan 30, 2011 at 6:30 AM, Paragon Corporation <lr at pcorp.us> wrote:
>
> Sunny,
>
>
>
> Good question.  I suspect it will be worse at least at the moment (just as
> PostGIS was worse when it first came out than reading from shapefile).  How
> much worse I'm not sure.  If you try and see speed issues, we can tackle
> them, but it hasn't really been our main focus.
>
>
>
>  I suspect no one has tested it extensively as far as dishing out large
> datasets.  The primary focus of PostGIS Raster is for analysis and then
> secondary is the rendering.  That is not to say it will work badly or we
> don't care about rendering speed, just that the GDAL drivers etc. needed by
> Mapserver probably still have a few wrinkles which would make it suboptimal
> for that kind of work.  The more people use it and find issues, the faster
> issues will be addressed since we would have data points to go by.
>
>
>
> As far as GeoServer goes, I recall reading a thread where Chris Holmes said
> he would work on a PostGIS Raster support for GeoServer, but not sure where
> that is down the pipe, but to my knowledge, GeoServer does not YET support
> PostGIS raster.
>
>
>
> Hope that helps,
>
> Regina
>
>
> ------------------------------
>
> *From:* postgis-users-bounces at postgis.refractions.net [mailto:
> postgis-users-bounces at postgis.refractions.net] *On Behalf Of *Sunny Teo
> *Sent:* Saturday, January 29, 2011 3:44 AM
> *To:* postgis-users at postgis.refractions.net
> *Subject:* [postgis-users] PostGIS Raster Performance
>
> List,
>
>
>
> Can anyone comment on the "Performance" of the PostGIS Rater or WKTRaster ?
>
>
>
> If you were to serve this onto a web application, how effective are they?
> Well, I'm talking of very large datasets like 10GB each and 100 of them. How
> does it compare with serving the images as files directly.. from a GeoTIFF,
> ECW, Sid, etc. (obviously using Geoserver/Mapserver or some specialized
> image serving solution)
>
>
>
> Been searching all over the web for the answers, but no luck.
>
>
>
> Hope to get some insights from the users.
>
>
>
>
>
>
>
> Thank you;
>
> Sunny.
>
>
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