[Gdal-dev] Gdal and pyramid files

[Frank Warmerdam]

Tim Sutton wrote:
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> Hi again
> 
> I have been comparing the performance of (gdal based) qgis against  * ahem * 
> arcmap using the Nasa blue marble visible earth dataset (two tiffs totalling 
> roughly 2.8gig). In general arcmap rendering is faster, especially when 
> zoomed out so that most or all of the dataset is in view.
> 
> I found the following message in the archives:
> 
> http://remotesensing.org/pipermail/gdal-dev/2003-August/000948.html
> 
> And was wondering if the use of rrd files is automatic in the gdal tiff 
> driver, or if there is something special I need to "activate"?

Tim,

GDAL does not use ArcMap .rrd files (really Erdas Imagine files) except
when the base file is an Erdas Imagine file.

> On a similar note, if I create overviews using the gdaladdo utilitiy, does 
> gdal automatically look for and use the associated .ovr file?

If GDAL supports building the overviews for a given format, then it will
auto-detect the .ovr file when reading and use for suitable resolution
requests.

> Lastly, is it possible call gdaladdo programmatically?

Certainly. The core method is the BuildOverviews() method on the GDALDataset
class.  You can look in gdal/apps/gdaladdo.cpp to see how it is called in C++.
There is a corresponding GDALBuildOverviews() C function as well.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent