[postgis-devel] [PostGIS] #2122: [raster] Real extent feature lost after metadata as views

[Bborie Park]

>
> "4. The right most column, and bottom row of blocks may have portions
> that extend beyond the raster extent. These areas will be assumed to be
> NODATA and not part of the described raster."
>
> http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01
>

After looking at that chunk as well as that page as whole, I still
haven't found anything that concretely defines the extent.  In EVERY
version of that spec page, the "extent" column of raster_columns is
described as:

"a polygon geometry containing all raster tiles, or NULL if predefined
bounds are not known. For "regular_blocking" cases this geometry will
be a simple rectangle. In other cases it might be an irregular
polygon. "

The only other items that discusses extent are:

1. A link to ST_Extent(geometry set):
http://postgis.refractions.net/documentation/manual-1.4/ST_Extent.html

2. A description to a non-existent function: "ST_Box2D(raster) ->
BOX2D - Returns a BOX2D representing the extent of the raster."

Due to the lack of an actual definition of what a raster extent is, I
have to fall back upon what PostGIS defines an extent as:

"an aggregate function that returns the bounding box that bounds rows
of geometries."

And based upon that, what is currently implemented is closest.

At the same time, if you're going to point out rule 4 of
regular_blocking as defining that a raster extent is only the extent
of where spatially the data is present, I may as well as point out
rule 1 of regular_blocking.

"All tiles must have the same size (blocksize_x and blocksize_y)."

-bborie