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Classify Points by Distance from a Border

Source: R/aoe_border.R
aoe_border.Rd

Given a set of points and a border (line), aoe_border() classifies points by their side relative to the border and their distance from it. Creates equal-area buffer zones on both sides of the border.

Usage

aoe_border(
  points,
  border,
  width = NULL,
  area = NULL,
  halo_width = NULL,
  halo_area = NULL,
  mask = NULL,
  bbox = NULL,
  side_names = c("side_1", "side_2"),
  coords = NULL
)

Arguments

points

An sf object with POINT geometries, or a data.frame with coordinate columns.

border

An sf object with LINESTRING or MULTILINESTRING geometry representing the border.

width

Buffer width in meters (for projected CRS) or degrees (for geographic CRS). Creates core zone within this distance of the border. Cannot be used together with area.

area

Target area for each side's core zone. The function finds the buffer width that produces this area per side. If mask is provided, the width is adjusted to achieve the target area after masking. Cannot be used together with width.

halo_width

Width of the halo zone beyond the core. If NULL (default), equals the core width for symmetric zones.

halo_area

Target area for each side's halo zone. Alternative to halo_width. If NULL and halo_width is NULL, defaults to equal area as core.

mask

Optional mask for clipping the buffer zones. Can be:

  • sf object with POLYGON or MULTIPOLYGON geometry

  • "land": use the bundled global land mask to exclude sea areas

bbox

Optional bounding box to limit the study area. Can be:

  • sf or sfc object (uses its bounding box)

  • Named vector: c(xmin = ..., ymin = ..., xmax = ..., ymax = ...)

  • NULL: no bbox restriction (uses buffer extent)

side_names

Character vector of length 2 naming the sides. Default is c("side_1", "side_2"). The first name is assigned to the left side of the border (when traversing from start to end).

coords

Column names for coordinates when points is a data.frame.

Value

An aoe_border_result object (extends sf) containing classified points with columns:

point_id

Original point identifier

side

Which side of the border: value from side_names

aoe_class

Distance class: "core" or "halo"

Points outside the study area are pruned (not returned).

Details

The function creates symmetric buffer zones around a border line:

  1. Core zone: Points within width (or area) distance of the border

  2. Halo zone: Points beyond core but within width + halo_width

  3. Pruned: Points outside the halo zone (not returned)

Each zone is split by the border line to determine which side the point falls on.

Equal area across sides

When using the area parameter, the buffer width is calculated to produce equal area on both sides of the border. With masking, the width is adjusted so that the masked area on each side equals the target.

Examples

library(sf)

# Create a border line
border <- st_as_sf(
  data.frame(id = 1),
  geometry = st_sfc(st_linestring(matrix(
    c(0, 0, 100, 100), ncol = 2, byrow = TRUE
  ))),
  crs = 32631
)

# Create points
pts <- st_as_sf(
  data.frame(id = 1:6),
  geometry = st_sfc(
    st_point(c(10, 20)),   # near border, side 1
    st_point(c(30, 10)),   # near border, side 2
    st_point(c(50, 80)),   # far from border, side 1
    st_point(c(80, 40)),   # far from border, side 2
    st_point(c(5, 5)),     # very close to border
    st_point(c(200, 200))  # outside study area
  ),
  crs = 32631
)

# Classify by distance from border
result <- aoe_border(pts, border, width = 20)