[Gdal-dev] optimum overview settings?

[Matt Wilkie]

Hi Listers,

What is the optimum number of overviews versus file size when stored in 
geotiffs? And if the end goal is viewing perfomance, as measured by an 
application like ArcMap? Mapserver?

The gdal_utilities web page[0] gives "2 4 8 16" as an example, however 
significant file size savings can be realized if we use just 4-16. What 
is sacrificed by dropping 2?

Are powers of two just convenience? Would 3 9 18 36 work just as well?

And does the size of the image determine how many overview levels are 
useful? For example a 100mb image might not benefit much from an upper 
overview of 16, while a 3gb image might need to go all the way up 128 or 
more.

Are there any guidelines for choosing overview levels?


[0] http://www.remotesensing.org/gdal/gdal_utilities.html

thanks for your time,

-- 
matt wilkie
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