visor (version 0.1.1)

get_isovist: Calculate isovist from one or multiple viewpoints

Description

Isovists are estimated by shooting a set of rays from each viewpoint, and by constructing the envelope of the (partially occluded) rays.

Usage

get_isovist(
  viewpoints,
  occluders = NULL,
  ray_num = 40,
  ray_length = 100,
  remove_holes = TRUE
)

Value

object of class sfc_POLYGON or sfc_MULTIPOLYGON

Arguments

viewpoints

object of class sf_POINT or sfc_POINT

occluders

object of class sf, sfc or sfg

ray_num

number of rays per viewpoint. The number of rays per quadrant needs to be a whole number, so ray_num will be rounded to the closest multiple of four

ray_length

length of rays

remove_holes

whether to remove holes from the overall isovist geometry

Examples

# Define viewpoints and occluder geometries
viewpoints <- sf::st_sfc(
  sf::st_point(c(-1, 1)),
  sf::st_point(c(0, 0)),
  sf::st_point(c(1, -1))
)
occluder1 <- sf::st_polygon(list(sf::st_linestring(
  cbind(c(-1, -1, -0.9, -0.9, -1),
        c(-1, -0.9, -0.9, -1, -1))
)))
occluder2 <- sf::st_polygon(list(sf::st_linestring(
  cbind(c(0.4, 0.4, 0.6, 0.6, 0.4),
        c(0.5, 0.7, 0.7, 0.5, 0.5))
)))
occluders <- sf::st_sfc(occluder1, occluder2)

# Calculare isovist based on 40 rays (default)
get_isovist(viewpoints, occluders, ray_length = 1.5)

# Increase number of rays to get higher resolution
get_isovist(viewpoints, occluders, ray_num = 400, ray_length = 1.5)