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.TH "GDAL_VIEWSHED" "1" "Mar 05, 2021" "" "GDAL"
.SH NAME
gdal_viewshed \- Calculates a viewshed raster from an input raster DEM for a user defined point
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.SH SYNOPSIS
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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>
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.SH DESCRIPTION
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By default the \fBgdal_viewshed\fP 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.
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\fBNOTE:\fP
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The algorithm as implemented currently will only output meaningful results
if the georeferencing is in a projected coordinate reference system.
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.TP
.B \-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.
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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.
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.TP
.B \-b <band>
Select an input band \fBband\fP 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.
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.B \-a_nodata <value>
The value to be set for the cells in the output raster that have no data.
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\fBNOTE:\fP
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Currently, no special processing of input cells at a nodata
value is done (which may result in erroneous results).
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.B \-ox <value>
The X position of the observer (in SRS units).
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.B \-oy <value>
The Y position of the observer (in SRS units).
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.B \-oz <value>
The height of the observer above the DEM surface in the height unit of the DEM. Default: 2
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.B \-tz <value>
The height of the target above the DEM surface in the height unit of the DEM. Default: 0
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.B \-md <value>
Maximum distance from observer to compute visibiliy.
It is also used to clamp the extent of the output raster.
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.B \-cc <value>
Coefficient to consider the effect of the curvature and refraction.
The height of the DEM is corrected according to the following formula:
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.ce
Height_{Corrected}=Height_{DEM}\-{CurvCoeff}\efrac{{TargetDistance}^2}{SphereDiameter}
.ce 0
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For atmospheric refraction we can use 0.85714
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.B \-iv <value>
Pixel value to set for invisible areas. Default: 0
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.B \-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
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.B \-vv <value>
Pixel value to set for visible areas. Default: 255
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.B \-om <output mode>
Sets what information the output contains.
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Possible values: VISIBLE, DEM, GROUND
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VISIBLE returns a raster of type Byte containing visible locations.
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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.
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Default VISIBLE
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.SH C API
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Functionality of this utility can be done from C with \fBGDALViewshedGenerate()\fP\&.
.SH EXAMPLE
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Compute the visibility of an elevation raster data source with defaults
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[image]
A computed visibility for two separate \fI\-ox\fP and \fI\-oy\fP points on a DEM..UNINDENT
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gdal_viewshed \-md 500 \-ox \-10147017 \-oy 5108065 source.tif destination.tif
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.IP [Wang2000] 5
Generating Viewsheds without Using Sightlines. Wang, Jianjun,
Robinson, Gary J., and White, Kevin. Photogrammetric Engineering and Remote
Sensing. p81. \fI\%https://www.asprs.org/wp\-content/uploads/pers/2000journal/january/2000_jan_87\-90.pdf\fP
.SH AUTHOR
Tamas Szekeres <szekerest@gmail.com>
.SH COPYRIGHT
1998-2021
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