Serving raster images via MapServer?

[Thom DeCarlo]

Hey Ed,
(So, you and Norm are over here, too. Small world!)

This sounds good. I've been reading up on the gdaltindex and I think I
understand how to get it set up. But, what is this shptree thing you
mentioned? 
Also, two other issues. First, the client is going to be continually
requesting map updates and the server will be getting frequent additions to
its repository. If the tile index is held in a shapefile will the MapServer
re-read that file when a new client request comes in or is it only read when
Mapserver starts?
Second, since I've already got a PostgreSQL server managing the vector data,
can the tile index be held in it, too? I'm going to have a lot of
overlapping imagery and it seems (to the novice that I am) that SQL queries
could find the best/newest data to serve out to the client. Or, is this just
unnecessary overhead?

Thanks!
Thom

--
Thom DeCarlo
--------------------------------------------------------
      Any sufficiently advanced technology
    is indistinguishable from a rigged demo.


> -----Original Message-----
> From: Ed McNierney
> Sent: Wednesday, March 29, 2006 3:36 PM
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: Re: [UMN_MAPSERVER-USERS] Serving raster images via MapServer?
> 
> Thom -
> 
> There are a few general principles for working with large raster data
> sets in MapServer.  Some of these are generalizations that apply to many
> similar applications and aren't necessarily MapServer-specific.
> 
> If your imagery is updated with any frequency, you'll want to simplify
> things and avoid lots of complex fiddling with the images.  For most
> users, it's good to keep the data on disks organized in a manner that's
> consistent with the way you receive the data and updates.
> 
> For performance reasons, GeoTIFF is almost always the preferred format.
> Compression generally costs you in performance, and particularly costs
> you in scalability; some decompressors run quickly but require lots of
> RAM.  That's fine for a small number of users, but if you scale up you
> may suffer as you can run out of physical RAM quickly.  Disk space is
> cheap - I never compress imagery.
> 
> If you can structure your GeoTIFFs to be internally tiled (using
> gdal_translate) with overviews (via gdaladdo) you can get GeoTIFFs that
> can be read quickly at a variety of scale levels.
> 
> Organize your GeoTIFFs using TILEINDEX shapefiles (via gdaltindex) and
> index those shapefiles with shptree.
> 
> Reprojection of raster data is faster than many folks think, but it's
> much slower than reprojecting vector data.  Where possible, store your
> imagery in the same projection as you serve it.
> 
> Keeping things simple is good - it's really not that complicated.  I'm
> currently providing WMS service (via MapServer) to just over 40
> terabytes of imagery in around 500,000 image files, using roughly the
> sort of system described above.
> 
> 	- Ed
> 
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> ed at topozone.com
> (978) 251-4242
> 
> -----Original Message-----
> From: Thom DeCarlo
> Sent: Wednesday, March 29, 2006 3:06 PM
> To: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: [UMN_MAPSERVER-USERS] Serving raster images via MapServer?
> 
> Hi,
> I've got a fairly large archive of raster images that we would like to
> deliver to remote clients through WMS. I've still got much to learn
> about the technology. I thought I should ask the first obvious question
> here.
> 
> Is there an accepted "best way" to organize and deliver imagery using
> MapServer? I have a PostgreSQL/PostGIS server set up to handle our
> vector data, but there doesn't seem to be support for raster data in
> that database.
> 
> Thanks,
> Thom
> --
> Thom DeCarlo
> --------------------------------------
>      That Which Does Not Kill Me
>      Can Still Hurt Really Bad.