viewscape (version 2.0.2)

compute_viewshed: compute_viewshed

Description

The compute_viewshed function is designed for computing viewsheds, which are areas visible from specific viewpoints, based on a Digital Surface Model (DSM). It provides flexibility for single or multi-viewpoint analyses and allows options for parallel processing, raster output, and plotting.

Usage

compute_viewshed(
  dsm,
  viewpoints,
  offset_viewpoint = 1.7,
  offset_height = 0,
  r = NULL,
  refraction_factor = 0.13,
  method = "plane",
  parallel = FALSE,
  workers = 1,
  raster = FALSE,
  plot = FALSE
)

Value

Raster or list. For single-viewpoint analysis, the function returns either a raster (raster is TRUE) or a viewshed object. Value 1 means visible while value 0 means invisible. For multi-viewpoint analysis, a list of viewsheds is returned.

Arguments

dsm

Raster, the digital surface model/digital elevation model

viewpoints

sf point(s) or vector including x,y coordinates of a viewpoint or a matrix including several viewpoints with x,y coordinates

offset_viewpoint

numeric, setting the height of the viewpoint. (default is 1.7 meters).

offset_height

numeric, setting the height of positions that a given viewpoint will look at. (defaut is 0)

r

Numeric (optional), setting the radius for viewshed analysis. (The default is 1000m/3281ft)

refraction_factor

Number, indicating the refraction factor. The refraction factor adjusts the effect of atmospheric refraction on the apparent curvature of the Earth. In most standard applications, a refraction factor of 0.13 is used, and so does this function. However, the appropriate refraction factor may vary depending on environmental conditions.

method

Character, The algorithm for computing a viewshed: "plane" and "los" (see details). "plane" is used as default.

parallel

Logical, (default is FALSE) indicating if parallel computing should be used to compute viewsheds of multiview points. When it is TRUE, arguements 'raster' and 'plot' are ignored

workers

Numeric, indicating the number of CPU cores that will be used for parallel computing. It is required if 'parallel' is 'TRUE'.

raster

Logical, (default is FALSE) if it is TRUE, the raster of viewshed will be returned. The default is FALSE

plot

Logical, (default is FALSE) if it is TRUE, the raster of viewshed will be displayed

Details

For method, "plane" is the reference plane algorithm introduced by Wang et al. (2000) and "los" is the line of sight algorithm (Franklin & Ray, 1994). The reference plane algorithm can be more time-efficient than the line of sight algorithm, whereas the accuracy of the line of sight is better.

References

Franklin, W. R., & Ray, C. (1994, May). Higher isn’t necessarily better: Visibility algorithms and experiments. In Advances in GIS research: sixth international symposium on spatial data handling (Vol. 2, pp. 751-770). Edinburgh: Taylor & Francis.

Wang, J., Robinson, G. J., & White, K. (2000). Generating viewsheds without using sightlines. Photogrammetric engineering and remote sensing, 66(1), 87-90.

See Also

fov_mask() visual_magnitude()

Examples

# Load a viewpoint
test_viewpoint <- sf::read_sf(system.file("test_viewpoint.shp", package = "viewscape"))
# load dsm raster
dsm <- terra::rast(system.file("test_dsm.tif", package ="viewscape"))
#Compute viewshed
output <- viewscape::compute_viewshed(dsm = dsm,
                                      viewpoints = test_viewpoint,
                                      offset_viewpoint = 6, r = 1600)