Generate an outer or inner boundary polygon by buffering an existing boundary

Computes an expanded or shrunken boundary by applying a spatial buffer to an existing polygon. The input can be either boundary points (as returned by getBoundary()) or polygon geometries (as returned by buildBoundaryPoly()). This is useful for defining outer spatial neighborhoods or for shrinking boundaries inward to define inner regions.

Usage

getOuterBoundary(boundary = NULL, dist = 100)

Arguments

boundary

A data frame of boundary points (with columns x, y, region_id) or an sf object.

dist

A numeric value specifying the buffer distance in spatial units. Use positive values to expand (outer boundary), and negative values to shrink (inner boundary). Default is 100.

Value

An sf object of expanded outer boundary polygons with the same region_id values as the original input.

Details

Be careful: when using a negative buffer distance (for inner boundaries), polygons may collapse, become invalid, or disappear entirely if the buffer width exceeds the shape's interior size.

See also

getInnerBoundary() for a simplified wrapper for inward shrinking.

Examples

# Load coordinates
coords <- readRDS(system.file("extdata", "MouseBrainCoords.rds",
    package = "SpNeigh"
))

# Get boundary points of cluster 2
boundary_points <- getBoundary(data = coords, one_cluster = 2)

# Build polygons from boundary points
boundary_polys <- buildBoundaryPoly(boundary_points)

# Generate outer boundaries with 100-unit buffer
outer1 <- getOuterBoundary(boundary_points, dist = 100)
outer2 <- getOuterBoundary(boundary_polys, dist = 100)

# Plot original and expanded boundaries
plot(boundary_polys)
plot(outer2, add = TRUE, border = "red")