[Mapserver-users] RE: Regarding very large raster files.

[Ed McNierney]

Gayathri -

I have not obtained any of that data from the seamless data distribution
system, but I do have quite a bit of it in the "bulk" master
distribution format.  That data is distributed in 5,000 x 5,000 pixel
tiles (i.e. a little less than one square mile) as uncompressed 24-bit
true-color GeoTIFFs.  As a result, each file is 75 megabytes (5K * 5K *
3), which is certainly a moderate size to handle with GDAL and
MapServer.  Color infrared DOQQ images are twice that size.

The seamless data appears to only be available (for this dataset) as
TIFF images, so if you want MrSID you'd need to do the compression
yourself.  You don't say how much data / what area you're acquiring, so
it's hard to tell.  If you have or can afford the disk space to store
the data as GeoTIFFs you will get better performance than MrSID images
(except possibly in extreme circumstances) and you will especially
benefit if you have many simultaneous users.  However, if disk space is
at a premium or your user load will be light, MrSID could be the better
choice.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com
-----Original Message-----
From: Swaminathan, Gayathri [mailto:gayathri at ou.edu] 
Sent: Wednesday, June 09, 2004 3:19 PM
To: Ed McNierney
Cc: mapserver-users at lists.gis.umn.edu
Subject: Regarding very large raster files.

Hi:

We are planning to get some 1-foot resolution orthos from the
seamless.gov 

But I have the following queries..and want to be sure of raster handling
before purchase.

1) Is MrSID a preferrable format?
	- My guess is no, correct? Although GDAL supports Mr.SID we are
taking about continuous decompression when the rasters are accessed
which is  
	definetely slower than direct access.
2) Is converting to TIFF the way to go?
	-But GDAL's supported formats link mentions that TIFF can have
max.size of only 4GB...

Any pointers on the above questions will be greatly useful....

Thanks
Gayathri