[gdal-dev] gdaladdo, overviews and NODATA

[Armin Burger]

Hi all

I have a question regarding the gdaladdo tool and NODATA pixels:

When using resampling like "average" it seems that along the border of 
DATA and NODATA pixels there happens an averaging also of some of the 
original NODATA pixels (looks like 1-2 pixel width). This way in the 
overviews they get values higher than 0 (0 is defined as NODATA). Using 
this type of data in mapserver leads to small black borders when the 
overviews are taken since the tag
   OFFSITE 0 0 0
does not work anymore for the small border of now only "nearly-black" 
pixels.

I tried to set the metadata NODATA of the images to 0 for each band but 
it had no effect. Only when I use resampling "nearest" then every NODATA 
pixel of the overviews retains the full black 0 0 0.

Is there a way to force to exclude NODATA pixels during the "average" 
resampling so that they retain their NODATA values?

Thanks
Armin