GeoTIFF overviews / TILEINDEX / Large dataset performance

[Ed McNierney]

Frank -

Yes - that's certainly true.  But I didn't think there was a substantial
difference between a single layer of TIFFs with in-image overviews vs. a
GROUP of layers with MINSCALE/MAXSCALE controls, each layer being an
independent set of resampled TIFFs.

The most important point, of course, is to minimize both the number of
files opened/read and the amount of resampling required for each
request.  Thanks for the help!

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: +1 (978) 251-4242
Fax: +1 (978) 251-1396
ed at topozone.com 

-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com] 
Sent: Monday, June 13, 2005 11:40 PM
To: Ed McNierney
Cc: MAPSERVER-USERS at lists.umn.edu
Subject: Re: [UMN_MAPSERVER-USERS] GeoTIFF overviews / TILEINDEX / Large
dataset performance

On 6/13/05, Ed McNierney <ed at topozone.com> wrote:
> There is a separate, independent effect due to the resampling of the 
> source data.  It is more expensive to resample an image ("zoom out" on
> it) than to display it at "native" resolution.  So to create the most 
> efficient source data for any given map request, you would (ideally) 
> read as few files as possible AND resample each file as little as 
> possible.

Ed,

This is true, but this effect is reduced by building "in image"
overviews since the required resolution of image data may be
approximately available. 

Best regards,
-- 
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