[postgis-users] rasters in PostGIS...

[Guido Lemoine]

Dear List,

Very interesting discussion on raster functionality. In general, I agree 
that
the image files should remain on disk. As a remote sensing user, I would
see benefits in the following "use cases":

1. sub-image extracts (e.g. for a polygon, along a line, or plane, for 
3D data);
2. running image processing routines (filters, histogram analysis, 
enhancement);
3. data look up (e.g. extract all pixels/regions with a certain [range 
of] values;
4. image classification (segmentation), which would be some combination 
of 1-3.

The db should handle *ALL* image metadata, including transformation between
image space and projections (avoiding reprojection of the images), look 
up tables,
tile indexing, etc. Problem is that in the remote sensing field alone, 
there are too
many image formats around, although GeoTIFF should be a good starting point.
Also, image metadata means different things to different users. For SAR, for
instance, we would be interested in storing all sorts of processing 
parameters from
the [CEOS] headers. Others may need much less details. So generalising 
this is not
trivial.

The suggestions to base any development on GDAL and OGR would avoid
reinventing the wheel (GDAL has quite a neat image data model). We also 
have
some experience with Java Advanced Imaging (JAI), which has a lot of 
sophisticated
image pyramid handling, Region Of Interest extraction, filtering and 
histogram
routines. I understand that JAI code is now in the Open Source domain 
(though not
sure).

Guido Lemoine


Matthew Perry wrote:

> I have no idea what it would take to truly implement rasters in 
> postgis but I've been lurking on this whole debate and I have two 
> major questions:
>
> 1. If you're going to run any useful SQL, your "atomic unit" has got 
> to be a single "cell", correct? What are the disk space costs of doing 
> this? I can imagine storing each cell of 16-bit tiff as a row in my 
> "raster table" would take massive amounts of disk space and be 
> painfully slow to access.
>
> 2. When selecting a raster what format would it return? There's no 
> WKT/GML/WKB equivalent in the raster world. You'd have to pick a 
> binary format but which one?
>
> Personally I'll just use GDAL (can r/w any number of raster formats) 
> along with OGR (can read/write postgis) along with python to script my 
> raster/postgis alogrithms.
>
> -- 
> Matt Perry
> perrygeo at gmail.com <mailto:perrygeo at gmail.com>
> http://www.perrygeo.net
>
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