How to use the command gdalbuildvrt (with examples)

GDAL (Geospatial Data Abstraction Library) is a powerful open-source command-line tool for reading, writing, and manipulating raster and vector geospatial data formats. One of the commands in the GDAL suite is gdalbuildvrt, which allows you to build virtual datasets from a list of existing datasets. This means you can create a virtual mosaic combining several raster files without actually merging them.

Use case 1: Make a virtual mosaic from all TIFF files contained in a directory

Code:

gdalbuildvrt path/to/output.vrt path/to/input_directory/*.tif

Motivation: This use case is useful when you have a directory with multiple TIFF files that you want to combine into a single mosaic. Instead of physically merging the files, you can create a virtual dataset (.vrt file) that references the individual files and serves as a single logical dataset.

Explanation:

• gdalbuildvrt is the command used to build a virtual dataset.
• path/to/output.vrt specifies the path and filename for the output .vrt file.
• path/to/input_directory/*.tif is a wildcard pattern that matches all TIFF files in the input directory.

Example output: The command will create a virtual mosaic in the specified output path, which can be opened and viewed as a single raster dataset containing all the TIFF files.

Use case 2: Make a virtual mosaic from files whose name is specified in a text file

Code:

gdalbuildvrt -input_file_list path/to/list.txt path/to/output.vrt

Motivation: This use case is helpful when you have a large number of files and want to specify the exact files to include in the virtual mosaic without manually typing their paths. By providing a text file containing the filenames, you can easily create a virtual dataset referencing those files.

Explanation:

• -input_file_list is the option used to specify that the list of input files is provided in a text file.
• path/to/list.txt is the path and filename of the text file containing the list of input files.
• path/to/output.vrt specifies the output path and filename for the virtual mosaic.

Example output: The command will create a virtual mosaic based on the list of files provided in the text file, generating an output .vrt file that can be opened and viewed as a single raster dataset.

Use case 3: Make an RGB virtual mosaic from 3 single-band input files

Code:

gdalbuildvrt -separate path/to/rgb.vrt path/to/red.tif path/to/green.tif path/to/blue.tif

Motivation: This use case is applicable when you have three single-band raster files representing the red, green, and blue channels of an RGB image. By using the -separate option, you can create a virtual mosaic that combines these channels into a single RGB image.

Explanation:

• -separate is the option indicating that the input files represent separate channels of an RGB image.
• path/to/rgb.vrt specifies the path and filename for the output virtual mosaic.
• path/to/red.tif, path/to/green.tif, and path/to/blue.tif are the paths and filenames of the three input single-band raster files.

Example output: The command will create an RGB virtual mosaic in the specified output path, consolidating the red, green, and blue channels of the input files into a single RGB image that can be viewed together.

Use case 4: Make a virtual mosaic with blue background color (RGB: 0 0 255)

Code:

gdalbuildvrt -hidenodata -vrtnodata "0 0 255" path/to/output.vrt path/to/input_directory/*.tif

Motivation: This use case is handy when you want to assign a specific background color to the virtual mosaic. In this example, we set the background color to blue (RGB value: 0 0 255).

Explanation:

• -hidenodata is the option that hides the nodata values, preventing them from being included in the virtual mosaic.
• -vrtnodata is the option used to specify the RGB color values for the nodata background.
• "0 0 255" is the RGB value representing the blue color.
• path/to/output.vrt specifies the output path and filename for the virtual mosaic.
• path/to/input_directory/*.tif is a wildcard pattern that matches all TIFF files in the input directory.

Example output: The command will create a virtual mosaic with a blue background color, excluding the nodata values from the individual TIFF files. The resulting .vrt file can be opened and viewed with the specified background color.