# `gdal raster aspect`

Added in version 3.11.

Generate an aspect map

## Synopsis

    Usage: gdal raster aspect [OPTIONS] <INPUT> <OUTPUT>

    Generate an aspect map

    Positional arguments:
      -i, --input <INPUT>                                  Input raster dataset [required]
      -o, --output <OUTPUT>                                Output raster dataset [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]
      --overwrite                                          Whether overwriting existing output is allowed
      -b, --band <BAND>                                    Input band (1-based index) (default: 1)
      --convention <CONVENTION>                            Convention for output angles. CONVENTION=azimuth|trigonometric-angle (default: azimuth)
      --gradient-alg <GRADIENT-ALG>                        Algorithm used to compute terrain gradient. GRADIENT-ALG=Horn|ZevenbergenThorne (default: Horn)
      --zero-for-flat                                      Whether to output zero for flat areas
      --no-edges                                           Do not try to interpolate values at dataset edges or close to nodata values

    Advanced Options:
      --if, --input-format <INPUT-FORMAT>                  Input formats [may be repeated]
      --oo, --open-option <KEY>=<VALUE>                    Open options [may be repeated]

## Description

gdal raster aspect generates an aspect map, from any GDAL-supported elevation raster.

This subcommand is also available as a potential step of gdal raster pipeline

It outputs a 32-bit float raster with values between 0° and 360° representing the azimuth that slopes are facing. The definition of the azimuth is such that: - 0° means that the slope is facing the North, - 90° it's facing the East, - 180° it's facing the South - and 270° it's facing the West (provided that the top of your input raster is north oriented).

The aspect value -9999 is used as the nodata value to indicate undefined aspect in flat areas with slope=0.

A nodata value in the target dataset will also be emitted if at least one pixel set to the nodata value is found in the 3x3 window centered around each source pixel. By default, the algorithm will compute values at image edges or if a nodata value is found in the 3x3 window, by interpolating missing values, unless `--no-edges` is specified, in which case a 1-pixel border around the image will be set with the nodata value.

### Standard options

-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 <BAND>

  Index (starting at 1) of the band to which the aspect must be computed.

--convention azimuth|trigonometric-angle

  Convention for output angles.

  Defaults to `azimuth`, that is to say: - 0° means that the slope is facing the North, - 90° it's facing the East, - 180° it's facing the South - and 270° it's facing the West (provided that the top of your input raster is north oriented).

  If set to `trigonometric-angle`, - 0° means that the slope is facing the East, - 90° it's facing the North, - 180° it's facing the West - and 270° it's facing the South

--gradient-alg Horn|ZevenbergenThorne

  Algorithm used to compute terrain gradient. The default is `Horn`. The literature suggests Zevenbergen & Thorne to be more suited to smooth landscapes, whereas Horn's formula to perform better on rougher terrain.

--zero-for-flat

  Whether to output zero for flat areas. By default, flat areas where the slope is null will be assigned a nodata value (-9999). When setting this option, they are set to 0.

--no-edges

  Do not try to interpolate values at dataset edges or close to nodata values

## 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: Generates an aspect map from a DTED0 file.

    $ gdal raster aspect n43.dt0 out.tif --overwrite