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# gdaladdo

builds or rebuilds overview images

## SYNOPSIS

    gdaladdo [-r {nearest,average,average_mp,average_magphase,mode}]
             [--help-general] 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 that is actually in TIFF format. The GeoTIFF driver stores overviews internally to the file operated on.

Overviews created in TIFF format may be compressed using the COMPRESS_OVERVIEW configuration option. All compression methods, supported by the GeoTIFF driver, available here. (eg --config COMPRESS_OVERVIEW DEFLATE)

Most drivers also support an alternate overview format using Erdas Imagine format. To trigger this use the USE_RRD=YES configuration option. This will place the overviews in an associated .aux file suitable for direct use with Imagine or ArcGIS as well as GDAL applications. (eg --config USE_RRD YES)

## EXAMPLE

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

Create an Erdas Imagine format overviews for the indicated JPEG file:

    gdaladdo --config USE_RRD YES airphoto.jpg 3 9 27 81

Generated for GDAL by 1.5.1.