gdaladdo

builds or rebuilds overview images

SYNOPSIS

gdaladdo [-r {nearest,average,average_mp,average_magphase,mode}]
         [-ro] [--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.

-ro:

open the dataset in read-only mode, in order to generate external overview (for GeoTIFF especially).

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, unless the -ro flag is specified.

External 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). The photometric interpretation can be set with --config PHOTOMETRIC_OVERVIEW {RGB,YCBCR,...}, and the interleaving with --config INTERLEAVE_OVERVIEW {PIXEL|BAND}.

To produce the smallest possible JPEG-In-TIFF overviews, you should use :

--config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config INTERLEAVE_OVERVIEW PIXEL

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 external JPEG-compressed GeoTIFF overview file from a 3-band RGB dataset:

gdaladdo --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR
         --config INTERLEAVE_OVERVIEW PIXEL rgb_dataset.ext 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

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Generated for GDAL by 1.5.1.