# `gdal raster mosaic`

Added in version 3.11.

Build a mosaic, either virtual (VRT) or materialized

## Synopsis

    Usage: gdal raster mosaic [OPTIONS] [<INPUTS>...] <OUTPUT>

    Build a mosaic, either virtual (VRT) or materialized.

    Positional arguments:
      -i, --input <INPUTS>                                            Input raster datasets (or specify a @<filename> to point to a file containing filenames) [1.. values]
      -o, --output <OUTPUT>                                           Output raster dataset (created by algorithm) [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:
      -f, --of, --format, --output-format <OUTPUT-FORMAT>             Output format ("GDALG" allowed)
      --co, --creation-option <KEY>=<VALUE>                           Creation option [may be repeated]
      -b, --band <BAND>                                               Input band(s) (1-based index) [may be repeated]
      --overwrite                                                     Whether overwriting existing output is allowed
      --resolution <xres>,<yres>|same|average|common|highest|lowest>  Target resolution (in destination CRS units) (default: same)
      --bbox <BBOX>                                                   Target bounding box as xmin,ymin,xmax,ymax (in destination CRS units)
      --target-aligned-pixels                                         Round target extent to target resolution
      --src-nodata <SRC-NODATA>                                       Set nodata values for input bands. [1.. values]
      --dst-nodata <DST-NODATA>                                       Set nodata values at the destination band level. [1.. values]
      --hide-nodata                                                   Makes the destination band not report the NoData.
      --add-alpha                                                     Adds an alpha mask band to the destination when the source raster have none.

## Description

This program builds a mosaic of a list of input GDAL datasets, that can be either a virtual mosaic in the VRT (Virtual Dataset) format, or in a more conventional raster format such as GeoTIFF.

The list of input GDAL datasets can be specified at the end of the command line or put in a text file (one filename per line) for very long lists. Wildcards '*', '?' or '['] of `VSIGlob()` can be used, even on files located on network file systems such as /vsis3/, /vsigs/, /vsiaz/, etc.

gdal raster mosaic does some checks to ensure that all files that will be put in the resulting file have similar characteristics: number of bands, projection, color interpretation, etc. If not, files that do not match the common characteristics will be skipped.

If the inputs spatially overlap, the order of the input list is used to determine priority. Files that are listed at the end are the ones from which the content will be fetched. Note that nodata will be taken into account to potentially fetch data from lower-priority datasets, but currently, alpha channel is not taken into account to do alpha compositing (so a source with alpha=0 appearing on top of another source will override its content). This might be changed in later versions.

The following options are available:

-f, --of, --format, --output-format <OUTPUT-FORMAT>

  Which output raster format to use. Allowed values may be given by `gdal --formats | grep raster | grep rw | sort`

--co <NAME>=<VALUE>

  Many formats have one or more optional creation options that can be used to control particulars about the file created. For instance, the GeoTIFF driver supports creation options to control compression, and whether the file should be tiled.

  May be repeated.

  The creation options available vary by format driver, and some simple formats have no creation options at all. A list of options supported for a format can be listed with the --formats command line option but the documentation for the format is the definitive source of information on driver creation options. See Raster drivers format specific documentation for legal creation options for each format.

--overwrite

  Allow program to overwrite existing target file or dataset. Otherwise, by default, gdal errors out if the target file or dataset already exists.

-b <band>

  Select an input <band> to be processed. Bands are numbered from 1. If input bands not set all bands will be added to the output. Multiple `-b` switches may be used to select a set of input bands.

--resolution {<xres,yres>|same|highest|lowest|average}

  In case the resolution of all input files is not the same, the `--resolution` flag enables the user to control the way the output resolution is computed.

  same, the default, checks that all source rasters have the same resolution and errors out when this is not the case.

  highest will pick the smallest values of pixel dimensions within the set of source rasters.

  lowest will pick the largest values of pixel dimensions within the set of source rasters.

  average will compute an average of pixel dimensions within the set of source rasters.

  common determines the greatest common divisor of the source pixel dimensions, e.g. 0.2 for source pixel dimensions of 0.4 and 0.6.

  <xres>,<yres>. The values must be expressed in georeferenced units. Both must be positive values.

--bbox <xmin>,<ymin>,<xmax>,<ymax>

  Set georeferenced extents of output file. The values must be expressed in georeferenced units. If not specified, the extent of the output is the minimum bounding box of the set of source rasters. Pixels within the extent of the output but not covered by a source raster will be read as valid pixels with a value of zero unless a NODATA value is specified using `--dst-nodata` or an alpha mask band is added with `--add-alpha`.

--target-aligned-pixels

  (target aligned pixels) align the coordinates of the extent of the output file to the values of the `--resolution`, such that the aligned extent includes the minimum extent. Alignment means that xmin / resx, ymin / resy, xmax / resx and ymax / resy are integer values.

--src-nodata <value>[,<value>]...

  Set nodata values for input bands (different values can be supplied for each band). If the option is not specified, the intrinsic nodata settings on the source datasets will be used (if they exist). The value set by this option is written in the NODATA element of each `ComplexSource` element.

--dst-nodata <value>[,<value>]...

  Set nodata values at the output band level (different values can be supplied for each band). If more than one value is supplied, all values should be quoted to keep them together as a single operating system argument (Example 1). If the option is not specified, intrinsic nodata settings on the first dataset will be used (if they exist). The value set by this option is written in the `NoDataValue` element of each `VRTRasterBand element`. Use a value of None to ignore intrinsic nodata settings on the source datasets.

--add-alpha

  Adds an alpha mask band to the output when the source raster have none. Mainly useful for RGB sources (or grey-level sources). The alpha band is filled on-the-fly with the value 0 in areas without any source raster, and with value 255 in areas with source raster. The effect is that a RGBA viewer will render the areas without source rasters as transparent and areas with source rasters as opaque.

--hide-nodata

  Even if any band contains nodata value, giving this option makes the output band not report the NoData. Useful when you want to control the background color of the dataset. By using along with the `--add-alpha` option, you can prepare a dataset which doesn't report nodata value but is transparent in areas with no data.

## GDALG output (on-the-fly / streamed dataset)

This program supports serializing the command line as a JSON file using the `GDALG` output format. The resulting file can then be opened as a raster dataset using the GDALG: GDAL Streamed Algorithm driver, and apply the specified pipeline in a on-the-fly / streamed way.

## Examples

### Example 1: Make a virtual mosaic with blue background colour (RGB: 0 0 255)

    gdal raster mosaic --hide-nodata --dst-nodata=0,0,255 doq/*.tif doq_index.vrt