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
)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_numwill 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)
#> Geometry set for 1 feature
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: -2.5 ymin: -2.5 xmax: 2.5 ymax: 2.5
#> CRS: NA
#> POLYGON ((2.426585 -1.463525, 2.33651 -1.680986...
# Increase number of rays to get higher resolution
get_isovist(viewpoints, occluders, ray_num = 400, ray_length = 1.5)
#> Geometry set for 1 feature
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: -2.5 ymin: -2.5 xmax: 2.5 ymax: 2.5
#> CRS: NA
#> POLYGON ((2.49926 -1.047116, 2.498335 -1.07066,...