[Gdal-dev] ArcSDE Support in GDAL/OGR

[Duarte Carreira]

Hi all.

I'm using ArcSDE for storing what we like to think are large raster
mosaics, although our scale may be a bit smaller than yours... Portugal
is small.

I would like to 'defend' the raster-in-database approach and also point
out why we like to use GDAL/OGR with our ArcSDE database.

I build raster mosaics by merging all images into a single table. As
each image is merged, pyramid levels are built for that area, turning
the mosaic into a kind of sid/ecw/jp2 huge file.

Now, about the advantages over file-based mosaics?
In my opinion they are the following:
 - I can extract a window extremely fast, and even choose the pyramid
level I want - in fact choosing the output resolution;
 - I can update a portion of the mosaic and rebuild pyramids for that
area, extremely fast;
 - I can add new areas just by importing a new image, extremely fast;
 - I can have all my desktop GIS users and Intranet and Internet users
accessing the same mosaic at what we perceive as an excellent
performance (and our servers are single-P4 based...) - I think the usual
RDBMS advantages apply here;
 - I am under the impression (but have no numbers to support this) that
big raster files in a file-share have less performance than accessing
the same information on a RDBMS - of course this varies with your LAN
and RDBMS, access patterns, and file sizes, but I feel this is really
true in our case here;
 - I prefer using mosaics over collections of independent rasters, since
I find managing collections to be more work-intensive, being referenced
or in the database;
 - ArcSDE integrates extremely well with ArcGIS and ArcIMS (but this is
obviously only important because we use ArcGIS and ArcIMS);

Why am I interested in having GDAL/OGR reading ArcSDE?
 - ArcGIS is slow exporting raster mosaics - we use ArcSDE command-line
utilities which are veeery fast;
 - ArcSDE command-line tools only export to TIF format;
 - I would prefer having GDAL exporting to a plethora of formats and
letting the user choose one;
 - I would prefer to use GDAL instead of ArcSDE command-line tools
because I feel I shouldn't have to install ArcSDE binaries on users'
PCs;
 - OGR read access to ArcSDE is important to me IF there are GIS desktop
tools that use it to access the data (I'm thinking QGIS or others...),
and IF mapservers use it (mapserver, geoserver, ...);
 - Finally, by using GDAL/OGR libs I can develop a small viewer in-house
that could show ArcSDE data (though I'm not considering it).

On a foot-note, I have stumbled on a few discussions about having
raster-data on a RDBMS or not. Isn't it just a matter of selecting the
right rows for the viewing window in both cases - vector and raster? I
feel the same reasoning applied to vector data should apply to raster
data. If you see advantages for the former the same should apply to the
later.

Regards,
Duarte Carreira

-----Mensagem original-----
De: Simon Perkins [mailto:sy at perkins.net] 
Enviada: quarta-feira, 4 de Julho de 2007 0:47
Para: Christopher Barker
Cc: gdal-dev
Assunto: Re: [Gdal-dev] ArcSDE Support in GDAL/OGR

Christopher Barker wrote:
>> I don't know any
>> other good cheap/free raster-in-database solutions.
>
> PostGIS can't do it? Darn.

There have been a couple of musings about raster support in PostGIS over
the last few years, but I haven't seen anything ready for primetime.

> Is it really critical that the rasters themselves be stored in the 
> database? Rather than say, references to files instead?

We may fall back on the file reference model, but our first preference
is to put all the data in the database. It's something of a marketing
strategy as well - all your data in one place.

Cheers,

Simon