[Gdal-dev] Creating overviews in different folder

Daniel B äck daniel112b at home.se
Wed Sep 29 09:08:36 EDT 2004

On Tue, 28 Sep 2004 11:04:09 -0400, Frank Warmerdam <warmerdam at pobox.com> wrote:
> Daniel Bäck wrote:
> > Yes i would like to use the overviews with the original file, supplying a
>  > location or name of the overview file in the call to GDALOpen or similar.
> Daniel,
> I am not keen on changing the GDALOpen() or overview generation API to
> start passing in names of overview files.

That's understandable.

> > The solution with the .vrt dataset might work out nicely for me, creating
>  > it with CreateCopy in the new location. Any immediate draw backs to this solution?
> The main downside other than complication is that raster access through
> a virtual file can be somewhat slower depending on how it is done.

I gave the .vrt dataset solution a try and i ran into some problems/questions.

1. If I create .vrt dataset with CreateCopy i can't build overviews for it by calling BuildOverviews. The CreateCopy method doesn't initialize the overview manager on the copy. Of course i can close the copy and then reopen it and then build the overviews but is it intended to work that way?

2. The .vrt dataset doesn't report the blocksize correctly, the VRTRasterBand initializes the block size to MIN(128,nXSize) in the initialize method. I'm not sure i have understood all possibilities with the .vrt dataset and it might just be a good reason to why it behaves like that, is it?



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