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Connect a sf LINESTRING object to border nodes of an sf POLYGON object

Source: R/desplim_connect_border.R
desplim_connect_border.Rd

Compute the optimal connections between nodes of a sf LINESTRING object and border nodes of a sf POLYGON object based on user input.

Usage

desplim_connect_border(
  input_linestring,
  input_polygon,
  input_buildings = NULL,
  distance_intersect = 500,
  distance_nodes = 250,
  minimum_angle = 30,
  num_candidates = 3
)

Arguments

input_linestring

object of class sf of type LINESTRING or MULTILINESTRING.

input_polygon

object of class sf of type POLYGON.

input_buildings

object of class sf of type POLYGON or MULTIPOLYGON. Contains elements which should not overlap with output border connetions. Default is NULL.

distance_intersect

numerical; the minimum distance from exsting intersections of input_linestring and the border of input_polygon for a border node of input_polygon to be considered for a new connection. Default is 500 units.

distance_nodes

numerical; maximum distance from the border nodes of input_polygon to for a node of input_linestring to be considered for a new connection. Default is 250 units.

minimum_angle

numerical; minimum angle between a new connection and the border of input_polygon required for the new connection to be c onsidered. Default is 30 degrees.

num_candidates

numerical; number of connections to attempt for each border node. Default is 3.

Value

An sf object of type LINESTRING connecting nodes in input_linestring to border nodes of input_polygon.

Details

For each candidate border node, num_candidates candidate connections are generated. Only candidate connections which meet the requirements of minimum_angle, are fully covered by the input polygon and do not cross any existing linestrings are selected. The border node closest to an existing intersection is considered first. If more than one valid connection for the border node is found, the shortest connection is selected and the set of other candidate border nodes is updated to exclude those who are within distance_intersect of the new connection. If no valid connection for the border node exist, the border node is removed from the set of candidate border nodes.

Examples

# Create input polygon
poly_coords <- list(matrix(
  c(0, 0, 10, 0, 16, 3, 10, 10, 0, 10, -4, 5, 0, 0),
  ncol = 2,
  byrow = TRUE
))
input_poly <- sf::st_sf(
  geometry = sf::st_sfc(sf::st_polygon(poly_coords), crs = 32612)
)

# Create input linestring
line_coords <- matrix(
  c(-4, 5, -2, 5, 7, 8, 9, 6, 9, 1),
  ncol = 2,
  byrow = TRUE
)
input_line <- sf::st_sf(
  geometry = sf::st_sfc(sf::st_linestring(line_coords), crs = 32612)
)

# Create input building(s)
building_coords <- list(matrix(
  c(3, 9, 9, 9, 9, 8.5, 3, 8.5, 3, 9),
  ncol = 2,
  byrow = TRUE
))
input_build <- sf::st_sf(
  geometry = sf::st_sfc(sf::st_polygon(building_coords), crs = 32612)
)

# Function call
border_connections <- desplim_connect_border(
  input_linestring = input_line,
  input_polygon = input_poly,
  input_buildings = input_build,
  distance_intersect = 3, # Small for example
  distance_nodes = 5, # Small for example
  minimum_angle = 30,
  num_candidates = 3
)

# Visualisation
plot(sf::st_geometry(input_poly), border = 'black', lwd = 2)
plot(sf::st_geometry(input_build), col = 'tomato3', add = TRUE)
plot(sf::st_geometry(input_line), col = 'olivedrab', lwd = 4, add = TRUE)
plot(
  sf::st_geometry(border_connections),
  col = 'slateblue3',
  lwd = 3,
  lty = 2,
  add = TRUE
)