[FWTools] overviews internal and macro tiling

Travis Kirstine GIS Tech tkirstine at jdbarnes.com
Thu Nov 3 09:06:58 EST 2005

I have some general questions regarding overviews and performance in
mapserver.  I've been going through the past user lists and it seems the
general consensus it that creating sets of images (small tiles to large
merged tiles) at different cell resolutions (reduced resolution as you zoom
out) that are activated by the MIN MAX Scale definitions in the mapfile is
the optimal why to go.  I was wondering is it still beneficial to create
internal overviews for these images using tool like gdaladdo.  I've been
doing some testing and don't see much of a change between aggregate images
and aggregate images with overview.  I was also hoping someone could  shed
some light around at what scale internal overviews are activated. For
instance our data is 0.20m pixel size 1 km square tiles and I run gdaladdo
on it

gdaladdo -r average image_1.tif 2 4 8 16 32

Right now its my understanding that the first level creates a resampled
internal image that is half the resolution 0.4m and second level would
resample the image to 0.8m resolution and so on.  If I'm zoomed all the way
in 1:1 and begin zooming out at what mapscale is the first overview level

Travis Kirstine
First Base Solutions Limited
140 Renfrew Dr, Suite 100
Markham ON
L3R 6B3
Phone 905.477.3600
Fax 905.477.3882
tkirstine at jdbarnes.com

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