[Gdal-dev] GDAL Postgis Raster Driver

[Benjamin Simon]

Roger,

If you mean "Why use a database engine to store rasters?" then the answer is :

- Use spatial queries among tables of rasters images (i.e extracting
the right image when given an address or any geocoded object)
- Benefit from the database storage assets  ( -> security, fast access
with spatial indexes, backup, ...)
- Merge your spatial raster data with any other data you may have in
your database

I think one can find many good reasons for using databases, it is just
a very powerfull tool for managing your data, whatever its type or
whatever the volume you have. You just need to have the good
structures inside your RDBMS to manipulate it. And that's what the
CHIP structure aims at.

On the other hand, if you just mean "Why use the Postgis CHIP C
structure instead of redesigning a more approriate new one ?" , then
the answer is :

- The Postgis CHIP type is quite well optimized, there could just be
minor improvments to it
and that's what i'm working on at the moment. If Postgis development
team doesn't want to modify the structure, then we might consider to
design a new type in PostgreSQL to store raster data or just cope with
it.

I hope you've found your answer in these words.

Regards,
Benjamin.


2005/8/31, Roger <roger at sylvanascent.com>:
> Ben,
> What are the advantages of using this chip scheme?
> 
> Roger
> 
> -----Original Message-----
> From: gdal-dev-bounces at lists.maptools.org
> [mailto:gdal-dev-bounces at lists.maptools.org] On Behalf Of Benjamin Simon
> Sent: Tuesday, August 30, 2005 5:58 AM
> To: gdal-dev at lists.maptools.org
> Subject: [Gdal-dev] GDAL Postgis Raster Driver
> 
> 
> Hi all,
> 
> I've been playing a bit with GDAL driver implementation and as I am quite
> interested in database development, I 've decided to write a Postgis wrapper
> for GDAL. I've used the Postgis CHIP datatype to store rasters in
> PostgreSQL.
> 
> Basically, the driver can read files with a pixel definition of 8 or 16
> bits. It can deal with 1 or 4 bands (GREY_SCALE, PALETTE and RGBA). I've
> only tested to import PNG, BMP, JPEG and TIF files and I think the driver is
> not stable yet with any other formats. The driver is supposed to be capable
> of dealing with projections if Postgis was built with the proj4 library.
> 
> I do think it could be good to move some of the functions from the GDAL
> Driver source code to Postgis source. However, this would require I contact
> Postgis development team and I prefer to finalize the driver before, as it
> is really easier to test and develop.
> 
> I have contacted Frank so that this new experimental driver can soon be part
> of the global GDAL source tree.
> 
> If you can't wait unil then or if you're interested in testing, you can
> download the source code from this address:
> http://simon.benjamin.free.fr/pgchip/ and follow the installation
> instructions.
> 
> Any suggestions, comments, questions or help are welcome.
> 
> Regards,
> Benjamin.
> 
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