[Mapserver-users] Raster Image Limitation

[Ed McNierney]

Rene -

To be honest, I highly recommend GeoTIFF.  You sound like your ECW files
are less than 10 gigabytes altogether; what kind of compression ratio
are you using?  If it's, say, 20:1 compression, then you'd have 200
gigabytes of uncompressed data.  200 gigabytes of disk space is pretty
cheap these days...

I do not recommend using any compression format, particularly
wavelet-style formats, when multiuser performance is important.
Decompressing these images quickly can be CPU and memory-intensive.
Particularly if you've got a memory-intensive decompressor, it may work
fine for light loads, but if you hit a few simultaneous users and run
out of physical RAM and start swapping (and you naturally haven't spent
money on fast swap disks <g>) things can deteriorate VERY quickly.

RAM is cheap, and disk is cheap.  Invest in both.  You don't have to go
wild spending money, but you will quickly spend several hundred dollars
in staff time trying to make your current config work, and a few hundred
dollars (even Canadian ones) will buy quite a bit of disk or RAM.

	- 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: Rene Teniere [mailto:TENIERER at gov.ns.ca] 
Sent: Thursday, April 15, 2004 11:52 AM
To: gerry.creager at tamu.edu; Ed McNierney
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] Raster Image Limitation

Thanks Ed, I was hoping you would respond. We have a similar site
running ArcIMS and it is also slow, however, it does not crash when
trying to access the images (It uses MrSID's). What format are you
using, and what would you recommend?

Rene

Rene J.R. Teniere - BSc., D.GIS
GIS Technician
Nova Scotia Department of Natural Resources Forestry Division (GIS) -
Truro

Phone: (902) 893-5655
Mobile: (902) 209-8956

>>> "Ed McNierney" <ed at topozone.com> 2004-04-15 12:42:34 PM >>>
Rene -

If the problem crops up with the high-resolution data only (i.e. the ECW
data) I would look to ECW first.  We certainly run several hundred users
at a time on a database of several hundred thousand raster images and
have no problems like you report; we do not, however, use ECW.

	- 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: Rene Teniere [mailto:TENIERER at gov.ns.ca]
Sent: Thursday, April 15, 2004 10:21 AM
To: gerry.creager at tamu.edu
Cc: mapserver-users at lists.gis.umn.edu
Subject: [Mapserver-users] Raster Image Limitation

Gerry,

I'll have to forward this off to the network admin in order to get those
answers for you.

Rene

>>> Gerry Creager N5JXS <gerry.creager at tamu.edu> 2004-04-15 11:03:04
AM
>>>
What are the particulars on the server?  Also, are you backing up to a

database, or is this solely the rasters?  (Sorry, I'm looking at it now,
but I've not had time to grok it all)... I'm thinking "Server" at this

point, as you're moving a lot of bits and thus have a lot of diskIO.

If you're talking 'bout a SCSI-based RAID5, you've got some of the
overhead covered.  If you're using a slow IDE disk, it's a lot worse.

Gerry

Rene Teniere wrote:
> Hi All,
> 
> We have a site that we want to go public (built using Chameleon
because
> my coded site is not ready yet and this had to be out ASAP) that
uses
a
> lot of rasters (410 indexed ecw's @ 18 - 25mb each). There are 4
other
> full images at much lower resolution that are scale dependent, once
you
> reach a certain scale the high res stuff kicks in. The problem is
that
> it works fine with one person, when multiple people use it, it craps

> out. We tested it out and it seems that it can only handle four high
res
> images at a time. Is this MapServer, ecw, or a server problem? Here
is
> the site:
> 
> http://nfis.gov.ns.ca/gmap/juan/index.phtml
> 
> Thanks for your time,
> 
> Rene
> 
> _______________________________________________
> Mapserver-users mailing list
> Mapserver-users at lists.gis.umn.edu
> http://lists.gis.umn.edu/mailman/listinfo/mapserver-users

--
Gerry Creager -- gerry.creager at tamu.edu 
Network Engineering -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Page: 979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843

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