Find internal boundaries (edges shared by exactly 2 features, opposite direction)

Find internal boundaries (edges shared by exactly 2 features, opposite direction)

Usage

find_internal_boundaries(x)

Arguments

x

A wkpool after merge_coincident

Value

A wkpool containing only internal boundary segments

Details

Internal boundaries are edges where one feature has segment (v0 -> v1) and another feature has (v1 -> v0), i.e. they share the edge but traverse it in opposite directions. This is the defining characteristic of a shared polygon boundary.

Examples

x <- wk::as_wkb(c(
  "POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))",
  "POLYGON ((1 0, 2 0, 2 1, 1 1, 1 0))"
))
pool <- establish_topology(x)
merged <- merge_coincident(pool)
find_internal_boundaries(merged)
#> <wkpool[2 segments, 6 vertices]>
#> [1] <segment: 2->3> <segment: 3->2>