[postgis-users] Raster tile size impact results
Pierre Racine
Pierre.Racine at sbf.ulaval.ca
Mon Jul 25 12:30:18 PDT 2016
I will need to see your last query to try to find the problem.
Pierre
From: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Pierre Bails
Sent: Wednesday, July 20, 2016 5:36 AM
To: PostGIS Users Discussion <postgis-users at lists.osgeo.org>
Subject: Re: [postgis-users] Raster tile size impact results
Hi,
Thank you for the tips.
Well, I don't know why, but the st_clip function doesn't seem work fine.
After clipping and dumping each pixel as point, some points follow tiles, others follow the geometry. Any idea why ?
For now, to avoid the problem, I apply a St_ContainsProperly after the dump.
[unnamed.png]
Red : geometry
Light blue : tiles
Dark blue : pixels as points
Thank you for your help !
Pierre
Le ven. 15 juil. 2016 à 17:28, Pierre Racine <Pierre.Racine at sbf.ulaval.ca<mailto:Pierre.Racine at sbf.ulaval.ca>> a écrit :
Sorry for the late answer.
You have to vectorize them on the fly from within OpenJump:
SELECT (ST_DumpAsPolygons(rast).* FROM yourrastertable;
If your raster is very big and tiled, just vectorize the tiles you need:
SELECT rid, rast::geometry FROM yourrastertable;
Look at the rids and then:
SELECT (ST_DumpAsPolygons(rast).* FROM yourrastertable
WHERE rid = x or rid = y
Pierre
> -----Original Message-----
> From: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org<mailto:postgis-users-bounces at lists.osgeo.org>] On Behalf
> Of Pierre Bails
> Sent: Friday, June 24, 2016 12:32 PM
> To: PostGIS Users Discussion <postgis-users at lists.osgeo.org<mailto:postgis-users at lists.osgeo.org>>
> Subject: Re: [postgis-users] Raster tile size impact results
>
> Hello,
>
> Unfortunatly, I don't find a way to print raster results in OpenJump. Can you
> explain me how I can do it ?
>
> Thank you for your help !
>
> Pierre
>
> Le lun. 20 juin 2016 à 16:16, Pierre Racine <Pierre.Racine at sbf.ulaval.ca<mailto:Pierre.Racine at sbf.ulaval.ca>
> <mailto:Pierre.Racine at sbf.ulaval.ca<mailto:Pierre.Racine at sbf.ulaval.ca>> > a écrit :
>
>
> I would try to understand, visually using OpenJump, how your tiles are
> clipped in the two cases... I guess sometimes 1 pixel wide tiles get clipped in a
> strange way.
>
> Pierre
>
> > -----Original Message-----
> > From: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org<mailto:postgis-users-bounces at lists.osgeo.org>
> <mailto:postgis-users-bounces at lists.osgeo.org<mailto:postgis-users-bounces at lists.osgeo.org>> ] On Behalf
> > Of Pierre Bails
> > Sent: Wednesday, June 15, 2016 11:41 AM
> > To: postgis-users at lists.osgeo.org<mailto:postgis-users at lists.osgeo.org> <mailto:postgis-<mailto:postgis->
> users at lists.osgeo.org<mailto:users at lists.osgeo.org>>
> > Subject: [postgis-users] Raster tile size impact results
> >
> > Hi all,
> >
> > I'm looking for get all pixel's value in a raster insert thanks to
> raster2pgsql
> > intersect by a polygon.
> > Nevertheless, there are some things that I don't understand: depends
> on tile
> > size, I don't have the same result... The error between 2 raster is also
> correlate
> > to the pixel size (I assume it's due to the pixel number).
> >
> > Can you explain me how the tile size can influence the final result ?
> >
> > Here is the query :
> > SELECT DISTINCT SUM((px).val)
> > FROM(
> > SELECT *
> > FROM mns INNER JOIN
> >
> st_setsrid(st_geomfromgeojson('{"type":"Polygon","coordinates":[[[x,y],[x,y],[x
> > ,y] ]]}'), 4326) as geom on ST_Intersects(mns.rast, geom)
> > ) AS clip, ST_PixelAsCentroids (ST_Clip(clip.rast, clip.geom),1) AS px;
> >
> >
> > DSM px size 70cm:
> > raster2pgsql -a -t 250x250 -s 4326 -F pathToDSM.tiff dsmTable (result:
> 46 347
> > 846)
> >
> > raster2pgsql -a -t 50x50 -s 4326 -F pathToDSM.tiff dsmTable : 46 382
> 873
> > Difference: 35027
> >
> >
> > DSM px size 20cm :
> > raster2pgsql -a -t 250x250 -s 4326 -F pathToDSM.tiff dsmTable : 567
> 505 888
> >
> > raster2pgsql -a -t 50x50 -s 4326 -F pathToDSM.tiff dsmTable : 596
> 897 610
> > Difference: 29 391 722
> >
> >
> > If we considere 250x250's result as reference, there is a difference of
> 0.07% in
> > the first case, and 5% in the second. If the polygon area increases, the
> error rate
> > increases.
> >
> > Thank you,
> >
> > Pierre
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