Error running gdaladdo on images with an internal overview

[brushtyler]

I get an error running gdaladdo on a geotiff with an internal overview.

I'm trying to create an external overview (-ro option) for the file but I get the following error:

ERROR 4: `../001.tif.ovr' does not exist in the file system,
and is not recognised as a supported dataset name.

Obviously 001.tif.ovr doesn't exist as 001.tif has an internal overview.

The same problem using as input a .img file with an internal overview, so I can suppose it's a general problem not related to the tiff format.

[Even Rouault]

I'm not sure what was your expectation from this experiment...

Are you just reporting that the error message is misleading (this should likely be fixed), or do you expect the GTiff and HFA drivers to be abloe to mix external overviews and internal overviews ?

The current behaviour is that the GTiff driver will only return internal overviews if they exist, and ignore completely the .tif.ovr file (the same applies for HFA driver)

[Even Rouault]

r22318 /trunk/gdal/frmts/ (gtiff/geotiff.cpp hfa/hfadataset.cpp): HFA and GTiff: add explicit error message when trying to add external overviews when there are already internal overviews (#4044)