Raster - TIF vs JPG

[Kralidis,Tom [Burlington]]

TIFFs w/ overviews provide efficient performance as the 'overviews' are the result of the GDAL utility gdaladdo, which (basically) creates snapshots of the TIFF file with a lower resolution, based on the scale(s) you choose.  So the TIFF draws quicker given a certain scale range, which eliminates the need to fetch the *actual* TIFF data at a, say, national scale.

So, a good option would be:

1./ use gdaladdo on each TIFF file
2./ use gdaltindex to create a tile index (shapefile) with file pointers to each TIFF
3./ reference the tile index shapefile in MapServer to display your TIFF data.

Also, see Chris Hodgson's presentation from MUM3/EOGEO 2005 for more info:

http://mapserver.gis.umn.edu/community/conferences/MUM3/present/session2/hodgsonppt/view

..Tom



________________________________

	From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Roland Martin
	Sent: 21 August, 2006 11:41 AM
	To: MAPSERVER-USERS at LISTS.UMN.EDU
	Subject: Re: [UMN_MAPSERVER-USERS] Raster - TIF vs JPG
	
	
	"Tiled TIFF files with overviews pre-built are one of the highest performance ways of serving large raster images."
	From: http://mapserver.gis.umn.edu/docs/howto/raster_data/?searchterm=raster%20tiff
	
	Not sure what it means by 'overviews', though!
	
	Presumably JPG images require decompression prior to creating the output image, whereas TIFFs can just be read straight off. 
	
	Cheers,
	Roland.
	
	
	
	
	On 21/08/06, Léveillé, James <James.Leveille at mtq.gouv.qc.ca> wrote: 

		Hi,
		 
		I have about 4 000 georeferenced images.
		I can use either TIF (with overviews) or JPG format.
		Which one should I use with MapServer ?
		Which one offers the most performance ?
		 
		Regards
		 
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