[Gdal-dev] optimum overview settings?

[Xiaodong Zhang]

Hi Frank,

Hope you don't mind my jumping into this discussion. Just want to double check
with you. I run overview at 2 4 8 16 for all the images using crontab. I noticed
the crontab did not run for a period of time and I don't know which images have
or not have overview. So I just run the overview again to all the images with
the same overview scheme 2 4 8 16. Will this create a duplicate overview of 2 4
8 16 2 4 8 16 as suggested by Martin, or as you have indicated it will simply
replace the existing matching overview layer.

Thanks
Xiaodong

Quoting Frank Warmerdam <warmerdam at pobox.com>:

> Matt Wilkie wrote:
> > Chapman, Martin wrote:
> > 
> >> Matt,
> >>
> >> Also, be aware that if you are writing an ovr file, and an ovr file with
> >> the same name exists, the gdal lib will append to the file, resulting in
> >> a file with more ovr's than you expect.  Moral of the story...delete the
> >> other ovr first.   
> 
> Martin / Matt,
> 
> Martin is right that you have to be wary about existing overviews.  gdaladdo
> attempts to add requested overview levels to existing levels or recreate
> existing levels if they match requested levels.
> 
> > What happens with geotiffs, where the overviews are embedded?
> 
> They cannot be easily deleted (like external files) so if you really want
> to get rid of them you pretty much have to gdal_translate the file to a new
> file which won't have 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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