Serving raster images via MapServer?

[Ed McNierney]

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: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of 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.