[postgis-users] Postgis Raster Performance

[Etienne B. Racine]

Hi Mauricio,

You're right, it sometimes can be quite slow to perform operations in
postgis. However, your question is kind of hard to answer as there is rarely
magic involved, there isn't one operation you must do to improve speed.
Maybe as Pierre suggested you could post your explain query so we know a bit
more about your operations. (You could explain your line intersection as
well, with the result you expected.) I've worked at finding a good
configuration for my specific operations, but it varies for another
operation and furthermore from an hardware to another.

As you said, having the latest SVN might help to improve speed.

Etienne

2011/7/15 Pierre Racine <Pierre.Racine at sbf.ulaval.ca>

> > I'm trying to use postgis raster analysis and I think that it's
> incredibly slow. I
> > wonder if there is a better raster organization for analysis.
> > I've tryed both tiled raster and single row raster and tiled raster was a
> little bit
> > faster when calling intersection.
>
> Could you give me a bit more information: What are you intersecting with
> what? Point, lines, polygons? (lines I guess) How many? How is your raster
> tiled? How big is it? Did you make sure the right index is used with an
> EXPLAIN?
>
> > I don't really understand the results of the intersection. I expected
> that the
> > command would give me a linestring with one coordinate more than the
> > linestring I gave. But instead it gives me many pieces of linestring.
> IMHO it's not
> > a very usefull result. I'd have to join them to get the profile.
>
> What do you expect this information/coordinate to be? The id of the
> intersecting raster? The mean of the intersecting pixel values? The pixel
> value for each piece of intersecting line? There is a different query for
> each and performance is different for each.
>
> Here I get people intersecting 100 000 lines with a 300 MB landsat image in
> 8 minutes and another intersecting 500 000 lidar points in 160 seconds. Do
> you consider this slow?
>
> Also did you read the tutorial?
> http://trac.osgeo.org/postgis/wiki/WKTRasterTutorial01
>
> In opposition to Jorge answer I must say that the gdal driver is not
> involved when doing raster/vector intersections in PostGIS.
>
> Pierre
>
>
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