.TH "gdaladdo" 1 "28 Jun 2006" "GDAL" \" -*- nroff -*-
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.SH NAME
gdaladdo \- gdaladdo
builds or rebuilds overview images
.SH "SYNOPSIS"
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.nf
gdaladdo [-r {nearest,average,average_mp,average_magphase,mode}]
                filename levels
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.SH "DESCRIPTION"
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The gdaladdo utility can be used to build or rebuild overview images for most supported file formats with one over several downsampling algorithms.
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.IP "\fB\fB-r\fP \fI{nearest,average,average_mp,average_magphase,mode}\fP:\fP" 1c
Select a resampling algorithm. 
.IP "\fB\fIfilename\fP:\fP" 1c
The file to build overviews for.  
.IP "\fB\fIlevels\fP:\fP" 1c
A list of integral overview levels to build.  
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\fIMode\fP is not actually implemented, and \fIaverage_mp\fP is unsuitable for use. \fIAverage_magphase\fP averages complex data in mag/phase space. \fINearest\fP and \fIaverage\fP are applicable to normal image data. \fINearest\fP applies a nearest neighbour (simple sampling) resampler, while \fIaverage\fP computes the average of all non-NODATA contributing pixels.
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Selecting a level value like \fI2\fP 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.
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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.
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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)
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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)
.SH "EXAMPLE"
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Create overviews, embedded in the supplied TIFF file:
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.nf
gdaladdo -r average abc.tif 2 4 8 16
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Create an external compressed GeoTIFF overview file from the ERDAS .IMG file:
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gdaladdo --config COMPRESS_OVERVIEW DEFLATE erdas.img 2 4 8 16
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Create an Erdas Imagine format overviews for the indicated JPEG file:
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.nf
gdaladdo --config USE_RRD YES airphoto.jpg 3 9 27 81
.fi
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.SH "AUTHORS"
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Frank Warmerdam <warmerdam@pobox.com>, Silke Reimer <silke@intevation.de>