[postgis-users] st_union(rast) returning null because of non alignment,

[Rhys A.D. Stewart]

So given that st_union is not the solution, how would I go about merging
two adjacent raster tiles?


On Wed, Nov 7, 2012 at 6:12 PM, Rhys A.D. Stewart <rhys.stewart at gmail.com>wrote:

> ok, well that may be the issue, I was trying to union a rasterised table
> of adjacent polygons. So will the corners may touch I doubt they overlap,
> but here is the output of st_metadata for two of the polygons that are
> adjacent:
>
> Clarendon 698486.043582936 617384.893096908 153 229 250 250 0 0 3448 4
> Manchester 683177.872077352 632613.85425893 117 182 250 250 0 0 3448 4
>
>
>
> On Wed, Nov 7, 2012 at 6:01 PM, Pierre Racine <Pierre.Racine at sbf.ulaval.ca
> > wrote:
>
>> By "on the same grid" I mean " at least one of any of the four corners of
>> any pixel of one raster falls on any corner of the grid of the other
>> raster" as stated in the ST_SameAlignment() doc.
>>
>> What is (are) the pixel size?
>>
>> > -----Original Message-----
>> > From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-
>> > bounces at lists.osgeo.org] On Behalf Of Rhys A.D. Stewart
>> > Sent: Wednesday, November 07, 2012 5:51 PM
>> > To: PostGIS Users Discussion
>> > Subject: Re: [postgis-users] st_union(rast) returning null because of
>> non
>> > alignment,
>> >
>> > Pierre,
>> >
>> > If by on the same grid you mean equal, then no hey are not. Here they
>> are.
>> >
>> >
>> > 1: POLYGON((766242.610093044 641994.463110607,779742.610093044
>> > 641994.463110607,779742.610093044 648494.463110607,766242.610093044
>> > 648494.463110607,766242.610093044 641994.463110607))
>> > 2:POLYGON((698486.043582936 617384.893096908,736736.043582936
>> > 617384.893096908,736736.043582936 674634.893096908,698486.043582936
>> > 674634.893096908,698486.043582936 617384.893096908))
>> >
>> > Thanks,
>> >
>> > Rhys
>> >
>> >
>> > On Wed, Nov 7, 2012 at 5:40 PM, Pierre Racine <
>> Pierre.Racine at sbf.ulaval.ca>
>> > wrote:
>> >
>> >
>> >       Hi Rhys,
>> >
>> >       Both rasters must also have their upperlefx and upperlefty on the
>> same
>> > grid.
>> >
>> >       Could you do:
>> >
>> >       SELECT ST_AsText(ST_ConvexHull(rast))
>> >
>> >       on both rasters and post the result here?
>> >
>> >       Thanks,
>> >
>> >       Pierre
>> >
>> >
>> >       > -----Original Message-----
>> >       > From: postgis-users-bounces at lists.osgeo.org [mailto:
>> postgis-users-
>> >       > bounces at lists.osgeo.org] On Behalf Of Rhys A.D. Stewart
>> >       > Sent: Wednesday, November 07, 2012 5:33 PM
>> >       > To: PostGIS Users Discussion
>> >       > Subject: [postgis-users] st_union(rast) returning null because
>> of non
>> > alignment,
>> >       >
>> >       > Greetings,
>> >       >
>> >       > according to the trusty docs online two rasters are aligned
>> when they
>> > share the
>> >       > same skew, scale and srid. Created a raster using st_asraster
>>  and
>> > according to
>> >       > st_metadata scale, skew and srid are all equal. Howvere st_unon
>> > complains
>> >       > saying that 'The two rasters provided do not have the same
>> alignment.
>> >       > Returning NULL'
>> >       >
>> >       > I noticed that  ticket #1336 as possibly relating to my issue,
>> but I'm not
>> > entirely
>> >       > sure. My posgis version is:
>> >       > POSTGIS="2.0.0 r9605" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.8.0,
>> 6
>> > March
>> >       > 2012" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8"
>> >       > LIBJSON="UNKNOWN" TOPOLOGY RASTER
>> >       >
>> >       >
>> >       > What am I missing or doing incorrectly?
>> >       >
>> >       > Regards,
>> >       >
>> >       > Rhys
>> >
>> >       _______________________________________________
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>> >
>> >
>>
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