[postgis-users] Re: Rasters (once more)

[Frank Warmerdam]

On 10/17/05, Patrick <pvanlaake at users.sourceforge.net> wrote:
> * Grid coordinate system starts at [0,0] in the upper-left corner. This may
> be extended by allowing grids coordinate systems to start in any corner and
> progress in any direction. Makes internal functionality quite a bit harder
> to write.
> * Rows and columns are supplied at the raster level, so all bands have those
> dimensions. This is one of my personal favourites, but I am open to
> discussion. Some logical combinations of bands would then be disallowed,
> such as Landsat thermal band, PAN band in several image formats, or ASTER
> band 3B vs VIS bands.

Patrick,

I prefer all bands in a raster to be of the same dimension as well.  If not,
the "raster" association between band objects becomes pretty vague.

This brings up another issue.  Your formulation does not seem to address
the georeferencing at all.  I normally associate georeferencing with the
raster (dataset in GDAL-speak) and this is one of the reasons that all the
bands are required to have the same size.

> * Bands are 2-dimensional. Could be changed, but I would like to hear some
> good arguments to do so.

This is very much my bias as well, but I am learning for the meteological,
and oceanography communities that my remote sensing / gis bias may be
limiting.  I think this might need some further consideration though bands
of more than 2 dimensions will substantially complicate some things.
Amoung other things, it would raise the question of whether we need
distinct bands, or whether a stack of 2D bands should just be a 3d object.

> * Many features still need to be added, such as palette information for
> integer types, and possibly a mechanism to link attributes.

Your proposed set of pixel types differs from that of GDAL in several regards.
You have various partial-byte types which GDAL lacks.  I can see real value
in the 1-bit type for masking but you might find it better eventually
to drop the
rest.  Likewise, I don't bother modelling a signed 8bit type.  It has
little utility
and can be easily handled by 16bit signed values where needed.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent