[postgis-users] Inconsistency between St_Value and ST_DumpAsPolygons

[Bborie Park]

ST_Value and ST_DumpAsPolygons do very different things. ST_Value gets a
value for a specific pixel while ST_DumpAsPolygons() dumps values by
merging pixels with same value in an area.

-bborie


On Thu, Jun 6, 2013 at 12:38 PM, Jean Marchal <jean.d.marchal at gmail.com>wrote:

> Dear List,
>
> value's number 4 in this raster come out with ST_Value:
>
> SELECT ST_Value(rast, 1, 8, 2), ST_BandnoDataValue(rast),
> ST_BandPixelType(rast)
> FROM (SELECT '
> 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'::raster
> rast) foo
>
> but not with ST_DumpAsPolygons:
>
> SELECT (ST_DumpAsPolygons(rast)).val
> FROM (SELECT
> '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'::raster
> rast) foo
>
> Is this a bug or I am doing something wrong ?
>
> Thanks,
>
> Jean
>
>
> --
> Jean Marchal
>
> Etudiant au doctorat / PHD student
> Université Laval - Pavillon Abitibi-Price
> Faculté de foresterie, de géographie et de géomatique
> 2405, rue de la Terrasse
> Québec (Québec) G1V 0A6
>
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