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Calculate signed area of a cycle

Source: R/merge_coincident.R
cycle_signed_area.Rd

Calculate signed area of a cycle

Usage

cycle_signed_area(cycle, pool)

Arguments

cycle

Integer vector of .vx IDs forming a closed cycle

pool

Vertex pool data frame (from pool_vertices)

Value

Numeric signed area.

Details

Uses the shoelace formula to compute signed area. The sign indicates winding direction. For typical geographic data (Simple Features convention):

  • Negative area = outer ring

  • Positive area = hole

This is intrinsic to the geometry: we observe winding, not declare it.

Examples

x <- wk::as_wkb("POLYGON ((0 0, 1 0, 1 1, 0 1, 0 0))")
pool <- establish_topology(x)
merged <- merge_coincident(pool)
cycles <- find_cycles(merged)
cycle_signed_area(cycles[[1]], pool_vertices(merged))
#> [1] 1