[postgis-users] Re: Re: Rasters (once more)
pvanlaake at users.sourceforge.net
Mon Oct 17 23:43:40 PDT 2005
On 17-Oct-2005, Frank Warmerdam <warmerdam at pobox.com> ever so gracefully
> 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.
The raster table contains an srid which references a coordinate system, a
single tie point in the form of ulx and uly, a pixel size, an implied grid
coordinate system starting at [0,0] in the upper-left corner, and an implied
north-orientation. What information is lacking?
The implied north-orientation is another point for discussion, by the way.
> > * 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.
I agree with you on both counts (the need and the complexity), and I am
"blessed" with the same bias as you are. I suppose that some input from the
meteorologic, atmospheric, oceanographic and geologic communities could be
very useful here. Two scenarios should at least be considered: 1) general
multidimensionality, potentially beyond 3D; and 2) time series. As you said,
everything can be solved with 2D bands, but more elegant and efficient (time
series) solutions may exist.
> Your proposed set of pixel types differs from that of GDAL in several
> You have various partial-byte types which GDAL lacks. I can see real
> 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.
The 2-bit and 4-bit types are in the OGC spec. I admit that I do not use
them myself, but there should still be a vast body of older satellite
imagery with 4-bit classification out there. Int8 is another borderline
case. Does anybody ever use it? Anyway, I don't think there is a major
penalty for supporting it.
In general, I prefer to stay as close to GDAL as possible (even if I use my
own home-grown Delphi DAL) so any help you can offer is greatly appreciated.
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