get_intersection: Spatial intersections with one or more geometries

In edwardlavender/flapper: Routines for the Analysis of Passive Acoustic Telemetry Data

Spatial intersections with one or more geometries

Description

This function is a wrapper for gIntersection that extracts the intersection between inputted geometries. Unlike gIntersection, the function requires geometries to be specified as a list. The intersections between all (one or more) specified geometries, excluding NULL elements, are returned.

Usage

get_intersection(x, ...)

Arguments

x

A list of Spatial* geometries supported by gIntersection. If x is a list with a single Spatial* element, that element is simply returned. If x is a list with two Spatial* elements, gIntersection is implemented directly to obtain the intersection. If x is a list with more than two Spatial* elements, gIntersection is implemented iteratively, effectively intersecting all geometries. NULL elements are ignored.

...

Arguments passed to gIntersection.

Value

The function returns a Spatial* object of the intersection between all inputted geometries.

Author(s)

Edward Lavender

See Also

gIntersection

Examples

## Define raster parameters (for sampling/plotting)
set.seed(1)
n <- raster::ncell(dat_gebco)
xy <- raster::coordinates(dat_gebco)
utm <- raster::crs(dat_gebco)
cols <- c("black", "red", "orange", "green", lwd = 2)
col_int <- scales::alpha("dimgrey", 0.5)

## Define example polygons
n_poly <- 4
polys <- lapply(1:n_poly, function(i) {
  xy_i <- xy[sample(1:n, 1), , drop = FALSE]
  xy_i <- sp::SpatialPoints(xy_i, utm)
  xy_i_buf <- rgeos::gBuffer(xy_i, width = 10000)
  return(xy_i_buf)
})

#### Example (1): Define intersections between multiple (here, four) polygons
# Plot area with polygons
raster::plot(dat_gebco)
lapply(1:length(polys), function(i) raster::lines(polys[[i]], col = cols[i]))
# Get intersection and add
int <- get_intersection(polys)
raster::plot(int, add = TRUE, col = col_int)

#### Example (2): Define intersections between fewer polygons
raster::plot(dat_gebco)
lapply(1:length(polys), function(i) raster::lines(polys[[i]], col = cols[i]))
raster::plot(get_intersection(polys[1:3]), add = TRUE, col = col_int)
raster::plot(get_intersection(list(polys[[1]], polys[[3]])), add = TRUE, col = col_int)

#### Example (3): The function can handle a single element
raster::plot(dat_gebco)
lapply(1:length(polys), function(i) raster::lines(polys[[i]], col = cols[i]))
raster::plot(get_intersection(polys[1]), add = TRUE, col = col_int)

#### Example (4): The function can handle NULL elements
raster::plot(dat_gebco)
lapply(1:length(polys), function(i) raster::lines(polys[[i]], col = cols[i]))
raster::plot(get_intersection(list(polys[[1]], NULL, NULL, polys[[4]])),
  add = TRUE, col = col_int
)

edwardlavender/flapper documentation built on Jan. 22, 2025, 2:44 p.m.