distanceToLine static method

double distanceToLine(Point<double> p, Point<double> start, Point<double> end)

Computes the distance on the sphere between the point p and the line segment from start to end.

Returns the distance in meters (assuming spherical earth).

Implementation

static double distanceToLine(final Point<double> p, final Point<double> start,
    final Point<double> end) {
  if (start == end) {
    return SphericalUtils.computeDistanceBetween(end, p);
  }

  final s0lat = SphericalUtils.toRadians(p.x);
  final s0lng = SphericalUtils.toRadians(p.y);
  final s1lat = SphericalUtils.toRadians(start.x);
  final s1lng = SphericalUtils.toRadians(start.y);
  final s2lat = SphericalUtils.toRadians(end.x);
  final s2lng = SphericalUtils.toRadians(end.y);

  final s2s1lat = s2lat - s1lat;
  final s2s1lng = s2lng - s1lng;
  final u = ((s0lat - s1lat) * s2s1lat + (s0lng - s1lng) * s2s1lng) /
      (s2s1lat * s2s1lat + s2s1lng * s2s1lng);

  if (u <= 0) {
    return SphericalUtils.computeDistanceBetween(p, start);
  } else if (u >= 1) {
    return SphericalUtils.computeDistanceBetween(p, end);
  }

  final latLng = Point(
    start.x + u * (end.x - start.x),
    start.y + u * (end.y - start.y),
  );
  return SphericalUtils.computeDistanceBetween(p, latLng);
}