Determines whether points lie inside a polygon.
Points located exactly on polygon edges or vertices are treated as inside.
Usage
ptInPoly(x, y, polyX, polyY)
Arguments
- x
numeric vector of x-coordinates of the query points.
- y
numeric vector of y-coordinates of the query points.
- polyX
numeric vector of x-coordinates of the polygon vertices.
- polyY
numeric vector of y-coordinates of the polygon vertices.
Value
an integer vector of length length(x):
- 0
point is outside the polygon.
- 1
point is inside the polygon or on its boundary.
Details
The function uses a numerically stable angle summation algorithm
implemented in C++ via Rcpp.
The polygon is implicitly closed (last vertex connects to the first).
The polygon is assumed to be non-self-intersecting.
Numerical robustness is ensured via epsilon-based comparisons.
Examples
# Define a square
px <- c(0, 1, 1, 0)
py <- c(0, 0, 1, 1)
# Query points
x <- c(0.5, 1.5, 0, 0.5)
y <- c(0.5, 0.5, 0, 1)
ptInPoly(x, y, px, py)
#> [1] 1 0 1 1
