.TH "gdaladdo" 1 "16 Sep 2004" "Doxygen" \" -*- nroff -*- .ad l .nh .SH NAME gdaladdo \- builds or rebuilds overview images .SH "SYNOPSIS" .PP .PP .PP .nf gdaladdo [-r {nearest,average,average_mp,average_magphase,mode}] filename levels .fi .PP .SH "DESCRIPTION" .PP The gdaladdo utility can be used to build or rebuild overview images for most supported file formats with one over several downsampling algorithms. .PP .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. .PP .PP \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. .PP 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. .PP 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. .SH "EXAMPLE" .PP .PP Create overviews, embedded in the supplied TIFF file: .PP .PP .nf gdaladdo -r average abc.tif 2 4 8 16 .fi .PP .PP Create an external compressed GeoTIFF overview file from the ERDAS .IMG file: .PP .PP .nf gdaladdo --config COMPRESS_OVERVIEW DEFLATE erdas.img 2 4 8 16 .fi .PP .SH "AUTHORS" .PP Frank Warmerdam Silke Reimer