[postgis-users] Raster Points in Polygon (was Re: PostGIS Raster for Met Data)

[Bryce L Nordgren]

postgis-users-bounces at postgis.refractions.net wrote on 08/25/2011 05:25:56 
PM:

> > If I understand this right, SRID 900917 is a custom coordinate system
> > for the (i,j) pixel coordinates of the image? Wouldn't this mean that
> > you have to have a different SRID for every tile (raster) of the
> > image, since each tile starts with (1,1)?
> 
> No. We deal with meteorological data rather than data images, and 
> apart from topography data (which can be pretty massive), none of 
> our raw data is tiled.

Understood. I think our issue is with the term "tile". If you store your 
massive data in more than one (say N) database rows, then you require N 
SRIDs to represent the N transforms from the within-the-tile coordinates 
to real world coordinates. If, however, the within-the-tile coordinates 
are first transformed to the (i,j) coordinates from the original grid 
(e.g., the coordinates from before you loaded it into your database), then 
you only need a single SRID. I did not see such a transformation in my 
cursory examination of the code posted to the list.

Even without a formal definition, the unique SRIDs should be used to 
distinguish between within-the-tile coordinates from different tiles 
(database rows). You'll then need another SRID to represent "original 
grid" coordinates.

Bryce
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