man gdaladdo (Commandes) - builds or rebuilds overview images

NAME

gdaladdo - builds or rebuilds overview images

SYNOPSIS

gdaladdo [-r {nearest,average,average_mp,average_magphase,mode}]
                filename levels

DESCRIPTION

The gdaladdo utility can be used to build or rebuild overview images for most supported file formats with one over several downsampling algorithms.

-r {nearest,average,average_mp,average_magphase,mode}:
Select a resampling algorithm.
filename:
The file to build overviews for.
levels:
A list of integral overview levels to build.

Mode is not actually implemented, and average_mp is unsuitable for use. Average_magphase averages complex data in mag/phase space. Nearest and average are applicable to normal image data. Nearest applies a nearest neighbour (simple sampling) resampler, while average computes the average of all non-NODATA contributing pixels.

Selecting a level value like 2 causes an overview level that is 1/2 the resolution (in each dimension) of the base layer to be computed. If the file has existing overview levels at a level selected, those levels will be recomputed and rewritten in place.

Some format drivers do not support overviews at all. Many format drivers store overviews in a secondary file with the extension .ovr. The GeoTIFF driver stores overviews internally to the file operated on. That file may be compressed. It is controlled via the COMPRESS_OVERVIEW system option. All compression methods, supported by the GeoTIFF driver, available here.

EXAMPLE

Create overviews, embedded in the supplied TIFF file: 

gdaladdo -r average abc.tif 2 4 8 16

Create an external compressed GeoTIFF overview file from the ERDAS .IMG file: 

gdaladdo --config COMPRESS_OVERVIEW DEFLATE erdas.img 2 4 8 16

AUTHORS

Frank Warmerdam <warmerdam@pobox.com> Silke Reimer <silke@intevation.de>