[Gdal-dev] Question about retreving a image from a geodatabase

[Douglas Coward]

I'm sorry,
 I know this is a pretty fundamental question to ask on this list, but I 
need to ask anyway.
 I am trying to understand geodatabases and how to build an application to 
work with one. I have search the Web and read books like Web Mapping 
Illustrated.  I am famillar with using the GDAL libraries in an application 
to load a GeoTIFF image, I have used the utilities like GDAL_translate in a 
command line interface and I am very famillar with Shapefiles.
  But I still don't understand the interaction of a C++ windows application 
retreving a raster image
from a geodatabase and the role of the GDAL/OGR libraries in this kind of 
exchange.

  My question is can anyone give me an example of the queries and the 
responses when a 
visualization application starts with a geographical rectangle and wants to 
query a PostGIS database for a raster image trimmed to fit that rectangle 
and how the image is returned to the application ready to be displayed?
   Being more specific....
  Is a raster image, like a landsat image, actually stored in the database, 
or is the image stored local to application and represented in the database 
by a bounding rectangle and the local filename?
  What happens when the queried rectangle overlaps more than one database 
image? How are the pieces composited together into one image?
  My only assumption right now is that the process begins with the 
application sending an SQL query through OGR to the PostGIS libraries for 
the rectangle in question. Beyond that I'm lost.
 
  Any replies will be appreciated. And if there is a link to a nuts and 
bolts kind of tutorial, I would very much appreciate that also.
 Thank you for your time.
  --Doug
 



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