# `gdal raster overview add`

Added in version 3.11.

Add overviews to a raster dataset

## Synopsis

    Usage: gdal raster overview add [OPTIONS] <DATASET>

    Adding overviews.

    Positional arguments:
      --dataset <DATASET>                Dataset (to be updated in-place, unless --external) [required]

    Common Options:
      -h, --help                         Display help message and exit
      --json-usage                       Display usage as JSON document and exit
      --config <KEY>=<VALUE>             Configuration option [may be repeated]
      --progress                         Display progress bar

    Options:
      --external                         Add external overviews
      -r, --resampling <RESAMPLING>      Resampling method. RESAMPLING=nearest|average|cubic|cubicspline|lanczos|bilinear|gauss|average_magphase|rms|mode
      --levels <LEVELS>                  Levels / decimation factors [may be repeated]
      --min-size <MIN-SIZE>              Maximum width or height of the smallest overview level.

    Advanced Options:
      --oo, --open-option <KEY>=<VALUE>  Open options [may be repeated]

## Description

gdal raster overview add can be used to build or rebuild overview images for most supported file formats with one of several downsampling algorithms.

--dataset <DATASET>

  Dataset name, to be updated in-place by default (unless `--external` is specified). Required.

--external

  Create external `.ovr` overviews as GeoTIFF files.

--resampling {nearest|average|cubic|cubicspline|lanczos|bilinear|gauss|average_magphase|rms|mode}

  Select a resampling algorithm. The default is `nearest`, which is generally not appropriate if sub-pixel accuracy is desired.

  When refreshing existing TIFF overviews, the previously used method, as noted in the RESAMPLING metadata item of the overview, will be used if `-r` is not specified.

  The available methods are:

  `nearest` applies a nearest neighbour (simple sampling) resampler.

  `average` computes the average of all non-NODATA contributing pixels. This is a weighted average taking into account properly the weight of source pixels not contributing fully to the target pixel.

  `bilinear` applies a bilinear convolution kernel.

  `cubic` applies a cubic convolution kernel.

  `cubicspline` applies a B-Spline convolution kernel.

  `lanczos` applies a Lanczos windowed sinc convolution kernel.

  `gauss` applies a Gaussian kernel before computing the overview, which can lead to better results than simple averaging in e.g case of sharp edges with high contrast or noisy patterns. The advised level values should be 2, 4, 8, ... so that a 3x3 resampling Gaussian kernel is selected.

  `average_magphase` averages complex data in mag/phase space.

  `rms` computes the root mean squared / quadratic mean of all non-NODATA contributing pixels

  `mode` selects the value which appears most often of all the sampled points.

--levels <level1,level2,...>

  A list of overview levels to build. Each overview level must be an integer value greater or equal to 2.

  When explicit levels are not specified,

  - If there are already existing overviews, the corresponding levels will be used to refresh them if no explicit levels are specified.

  - Otherwise, appropriate overview power-of-two factors will be selected until the smallest overview is smaller than the value of the `--min-size` switch.

--min-size <val>

  Maximum width or height of the smallest overview level. Only taken into account if explicit levels are not specified. Defaults to 256.

## Examples

### Example 1: Create overviews, embedded in the supplied TIFF file, with automatic computation of levels

    gdal raster overview add -r average abc.tif

### Example 2: Create overviews, embedded in the supplied TIFF file

    gdal raster overview add -r average --levels=2,4,8,16 abc.tif

### Example 3: Create an external compressed GeoTIFF overview file from the ERDAS .IMG file

    gdal raster overview add --external --levels=2,4,8,16 --config COMPRESS_OVERVIEW=DEFLATE erdas.img

### Example 4: Create an external JPEG-compressed GeoTIFF overview file from a 3-band RGB dataset

If the dataset is a writable GeoTIFF, you also need to add the `--external` option to force the generation of external overview.

    gdal raster overview add --config COMPRESS_OVERVIEW=JPEG --config PHOTOMETRIC_OVERVIEW=YCBCR
             --config INTERLEAVE_OVERVIEW=PIXEL rgb_dataset.ext 2 4 8 16

### Example 5: Create overviews for a specific subdataset

For example, one of potentially many raster layers in a GeoPackage (the "filename" parameter must be driver prefix, filename and subdataset name, like e.g. shown by gdalinfo):

    gdal raster overview add GPKG:file.gpkg:layer