viewshed function

Compute a viewshed

Use elevation data to compute the locations that can be seen, or how much higher they would have to be to be seen, from a certain position. The raster data coordinate reference system must planar (not lon/lat), with the elevation values in the same unit as the distance unit of the coordinate reference system.

## S4 method for signature 'SpatRaster'
viewshed(x, loc, observer=1.80, target=0, curvcoef=6/7, output="yes/no", filename="", ...)

Arguments

• x: SpatRaster, single layer with elevation values. Values should have the same unit as the map units
• loc: location (x and y coordinates) or a cell number
• observer: numeric. The height above the elevation data of the observer
• target: numeric. The height above the elevation data of the targets
• curvcoef: numeric. Coefficient to consider the effect of the curvature of the earth and refraction of the atmosphere. The elevation values are corrected with: elevation = elevation - curvcoeff * (distance)^2 / (earth_diameter). This means that with the default value of 0.85714, you lose sight of about 1 meter of elevation for each 385 m of planar distance
• output: character. Can be "yes/no" to get a binary (logical) output showing what areas are visible; "land" to get the height above the current elevation that would be visible; or "sea" the elevation above sea level that would be visible
• filename: character. Output filename
• ...: Options for writing files as in writeRaster

See Also

terrain

References

The algorithm used is by Wang et al.: https://www.asprs.org/wp-content/uploads/pers/2000journal/january/2000_jan_87-90.pdf.

Examples

f <- system.file("ex/elev.tif", package="terra")
r <- rast(f)
x <- project(r, "EPSG:2169")
p <- cbind(70300, 96982)
v <- viewshed(x, p, 0, 0, 0.85714)