# gdal_viewshed

Calculates a viewshed raster from an input raster DEM using method defined in [Wang2000] for a user defined point.

New in version 3.1.0.

## Synopsis

    gdal_viewshed [-b <band>]
                  [-a_nodata <value>] [-f <formatname>]
                  [-oz <observer_height>] [-tz <target_height>] [-md <max_distance>]
                  -ox <observer_x> -oy <observer_y>
                  [-vv <visibility>] [-iv <invisibility>]
                  [-ov <out_of_range>] [-cc <curvature_coef>]
                  [[-co NAME=VALUE] ...]
                  [-q] [-om <output mode>]
                  <src_filename> <dst_filename>

## Description

By default the gdal_viewshed generates a binary visibility raster from one band of the input raster elevation model (DEM). The output raster will be of type Byte. With the -mode flag can also return a minimum visible height raster of type Float64.

Note

The algorithm as implemented currently will only output meaningful results if the georeferencing is in a projected coordinate reference system.

`-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.

  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.

`-b``<band>`

  Select an input band band containing the DEM data. Bands are numbered from 1. Only a single band can be used. Only the part of the raster within the specified maximum distance around the observer point is processed.

`-a_nodata``<value>`

  The value to be set for the cells in the output raster that have no data.

  Note

  Currently, no special processing of input cells at a nodata value is done (which may result in erroneous results).

`-ox``<value>`

  The X position of the observer (in SRS units).

`-oy``<value>`

  The Y position of the observer (in SRS units).

`-oz``<value>`

  The height of the observer above the DEM surface in the height unit of the DEM. Default: 2

`-tz``<value>`

  The height of the target above the DEM surface in the height unit of the DEM. Default: 0

`-md``<value>`

  Maximum distance from observer to compute visibiliy. It is also used to clamp the extent of the output raster.

`-cc``<value>`

  Coefficient to consider the effect of the curvature and refraction. The height of the DEM is corrected according to the following formula:

  \[Height_{Corrected}=Height_{DEM}-{CurvCoeff}\frac{{TargetDistance}^2}{SphereDiameter}\]

  For atmospheric refraction we can use 0.85714

`-iv``<value>`

  Pixel value to set for invisible areas. Default: 0

`-ov``<value>`

  Pixel value to set for the cells that fall outside of the range specified by the observer location and the maximum distance. Default: 0

`-vv``<value>`

  Pixel value to set for visible areas. Default: 255

`-om``<output mode>`

  Sets what information the output contains.

  Possible values: VISIBLE, DEM, GROUND

  VISIBLE returns a raster of type Byte containing visible locations.

  DEM and GROUND will return a raster of type Float64 containing the minimum target height for target to be visible from the DEM surface or ground level respectively. Flags -tz, -iv and -vv will be ignored.

  Default VISIBLE

## C API

Functionality of this utility can be done from C with `GDALViewshedGenerate()`.

## Example

Compute the visibility of an elevation raster data source with defaults

A computed visibility for two separate -ox and -oy points on a DEM.

    gdal_viewshed -md 500 -ox -10147017 -oy 5108065 source.tif destination.tif

Wang2000

  Generating Viewsheds without Using Sightlines. Wang, Jianjun, Robinson, Gary J., and White, Kevin. Photogrammetric Engineering and Remote Sensing. p81. https://www.asprs.org/wp-content/uploads/pers/2000journal/january/2000_jan_87-90.pdf