[Gdal-dev] Building overviews in external .ovr file programatticall

[Tim Sutton]

Hi

Sorry my original message was not very clearly put. I have already
 implemented an overview builder in QGIS (since 0.6 release). Looking at the
 gdaladdo code, its not substantially different to what I have implemented.
 Some users filed bugs about QGIS not producing overviews for certain file
 types e.g. jpg. So I went back to the gdal docs (the gdaladdo docs instead
 of the api docs I previously used) to try to see what the supported file
 types were and then realised that it mentions the ability to e.g. build ovr
 files. On closer investigation however, I have discovered the real problem
 was that I was not handling errors correctly as I'd stubbed out bits of
 error handling code based on gdal api docs that didn't work. To resolve the
 problem I had a poke around in the gdal sources and discovered the following
 small errors in the api docs:

GDALDataset::BuildOverviews 'CPLE_NonSupported' should read
'CPLE_NotSupported'.

The same error is also in GDALRasterBand::BuildOverviews.

Also these same docs sections state that an error can be picked up using
CPLGetLastError(), but after a bit of snooping around in the source is looks
like its actually CPLGetLastErrorNo() that should be used.

That allowed me to implement a better error handler and will hopefully
 resolve my problem mostly.

Hope thats useful :-)

Regards

Tim

On Monday 25 July 2005 16:07, Frank Warmerdam wrote:
> On 7/24/05, Tim Sutton <tim at linfiniti.com> wrote:
> > Hi
> >
> > The docs mention the ability to build .ovr files, but I dont see any way
> > to force the behaviour programmatically. Are .ovr files supported on all
> > formats? Is there a list of supported overview friendly formats if not?
>
> Tim,
>
> Check out the BuildOverviews() method on the GDALDataset for
> information on how to build overviews programmatically.
>
> http://www.gdal.org/classGDALDataset.html#a24
>
> I would add that the gdaladdo source is quite short and you can
> look at it.
>
> There is no clear way to figure out what formats support overviews.
> Most do, but not all.
>
> Best regards,

--
"The mind once expanded to the dimensions of larger ideas never returns to
 its original dimensions."

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