Re: [UMN_MAPSERVER-USERS] Serving raster images via MapServer?

Thu, 30 Mar 2006 17:28:34 -0800

Wow, Armin's solution (using PostGIS as the tileindex) is well nigh perfect. Have an image metadata table with nice information like capture date, sensor, whatnot, and the path reference to the raw data... then using the arbitrary SQL capabilities of Mapserver/ PostGIS set up to do the "latest-and-greatest" query. For a PoC you could just do a latest-limit-1 query. For a real one, you'll probably have to do some pl/pgsql in order to reduce the return set to just the minimal latest overlapping set. Could be v. v. slick. 

P.

On Mar 30, 2006, at 7:47 AM, Thom DeCarlo wrote:


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: [email protected]
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
[EMAIL PROTECTED]
(978) 251-4242

-----Original Message-----
From: Thom DeCarlo
Sent: Wednesday, March 29, 2006 3:06 PM
To: [email protected]
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.

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