# `gdal raster slope`

Added in version 3.11.

Generate a slope map

## Synopsis

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

    Generate a slope 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)
      --unit <UNIT>                                        Unit in which to express slopes. UNIT=degree|percent (default: degree)
      --xscale <XSCALE>                                    Ratio of vertical units to horizontal X axis units
      --yscale <YSCALE>                                    Ratio of vertical units to horizontal Y axis units
      --gradient-alg <GRADIENT-ALG>                        Algorithm used to compute terrain gradient. GRADIENT-ALG=Horn|ZevenbergenThorne (default: Horn)
      --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 slope generates a slope map, from any GDAL-supported elevation raster.

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

It generates a 32-bit float raster with slope values. You have the option of specifying the type of slope value you want: degrees or percent slope. In cases where the horizontal units differ from the vertical units, you can also supply scaling factors to account for differences between vertical and horizontal units.

The value -9999 is used as the output nodata value. A nodata value in the target dataset will 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.

In general, it assumes that x, y and z units are identical. However, if none of `--xscale` and `--yscale` are specified, and the CRS is a geographic or projected CRS, it will automatically determine the appropriate ratio from the units of the CRS, as well as the potential value of the units of the raster band (as returned by `GDALRasterBand::GetUnitsType()`, if it is metre, foot international or US survey foot). Note that for geographic CRS, the result for source datasets at high latitudes may be incorrect, and prior reprojection to a polar projection might be needed using gdal raster reproject.

If x (east-west) and y (north-south) units are identical, but z (elevation) units are different, the `--xscale` and `--yscale` can be used to set the ratio of vertical units to horizontal. For geographic CRS near the equator, where units of latitude and units of longitude are similar, elevation (z) units can be converted to be compatible by using scale=370400 (if elevation is in feet) or scale=111120 (if elevation is in meters). For locations not near the equator, the `--xscale` value can be taken as the `--yscale` value multiplied by the cosine of the mean latitude of the raster.

### 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 slope must be computed.

--unit degree|percent

  Unit in which to express slopes. Defaults to `degree`.

--xscale <scale>

  Ratio of vertical units to horizontal X axis units. If the horizontal unit of the source DEM is degrees (e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical units are meters (or scale=370400 if they are in feet).

  If none of `--xscale` and `--yscale` are specified, and the CRS is a geographic or projected CRS, gdal raster slope will automatically determine the appropriate ratio from the units of the CRS, as well as the potential value of the units of the raster band (as returned by `GDALRasterBand::GetUnitsType()`, if it is metre, foot international or US survey foot). Note that for geographic CRS, the result for source datasets at high latitudes may be incorrect, and prior reprojection to a polar projection might be needed.

  If `--xscale` is specified, `--yscale` must also be specified.

--yscale <scale>

  Ratio of vertical units to horizontal Y axis units. If the horizontal unit of the source DEM is degrees (e.g Lat/Long WGS84 projection), you can use scale=111120 if the vertical units are meters (or scale=370400 if they are in feet)

  If none of `--xscale` and `--yscale` are specified, and the CRS is a geographic or projected CRS, gdal raster slope will automatically determine the appropriate ratio from the units of the CRS, as well as the potential value of the units of the raster band (as returned by `GDALRasterBand::GetUnitsType()`, if it is metre, foot international or US survey foot). Note that for geographic CRS, the result for source datasets at high latitudes may be incorrect, and prior reprojection to a polar projection might be needed.

  If `--yscale` is specified, `--xscale` must also be specified.

--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.

--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 a slope map from a DTED0 file.

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