[Gdal-dev] viewing gdaladdo overlays

Frank Warmerdam warmerdam at pobox.com
Tue Jul 15 23:23:32 EDT 2003

Benjamin Wragg wrote:
> Hi list,
> If I built 4 overlays in a geotiff using gdaladdo, is it possible to 
> view each overlay in some type of GIS/Graphical program? If so what 
> programs support this?


Some programs that support TIFF will let you look at specific sub-images
but this if fairly rare.  An alternative is to use the "tiffsplit"
utility distributed with libtiff to split each TIFF directory into a
seperate file.  That would mean the base image, and each overview would
be a seperate TIFF file. Some information (like the geotiff tags) might be
lost in this process.

Of course, applications that support overviews in TIFF will presumably let
you see the overview levels implicitly.  For instance, if you load an
image in OpenEV that has overviews, go to 1:1 resolution, and then
page out each step should show a different power of 2 overview (assuming
you built your overviews on powers of two).  But it can be hard to be sure
you are getting what you think you should be getting.  I assume you are wanting
to do some quality assurance on the overviews?

Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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