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use num_traits::{Float, FromPrimitive};
use ::Point;
/// Returns the bearing to another Point in degrees.
///
/// Bullock, R.: Great Circle Distances and Bearings Between Two Locations, 2007.
/// (https://dtcenter.org/met/users/docs/write_ups/gc_simple.pdf)
pub trait Bearing<T: Float> {
/// Returns the bearing to another Point in degrees, where North is 0° and East is 45°.
///
/// ```
/// # extern crate geo;
/// # #[macro_use] extern crate approx;
/// #
/// use geo::Point;
/// use geo::algorithm::bearing::Bearing;
///
/// # fn main() {
/// let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
/// let p_2 = Point::<f64>::new(9.274410083250379, 48.84033282787534);
/// let bearing = p_1.bearing(p_2);
/// assert_relative_eq!(bearing, 45., epsilon = 1.0e-6);
/// # }
/// ```
fn bearing(&self, point: Point<T>) -> T;
}
impl<T> Bearing<T> for Point<T>
where T: Float + FromPrimitive
{
fn bearing(&self, point: Point<T>) -> T {
let (lng_a, lat_a) = (self.x().to_radians(), self.y().to_radians());
let (lng_b, lat_b) = (point.x().to_radians(), point.y().to_radians());
let delta_lng = lng_b - lng_a;
let s = lat_b.cos() * delta_lng.sin();
let c = lat_a.cos() * lat_b.sin() - lat_a.sin() * lat_b.cos() * delta_lng.cos();
T::atan2(s, c).to_degrees()
}
}
#[cfg(test)]
mod test {
use super::*;
use algorithm::bearing::Bearing;
use algorithm::haversine_destination::HaversineDestination;
#[test]
fn returns_the_proper_bearing_to_another_point() {
let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
let p_2 = p_1.haversine_destination(45., 10000.);
let b_1 = p_1.bearing(p_2);
assert_relative_eq!(b_1, 45., epsilon = 1.0e-6);
let p_3 = Point::<f64>::new(9., 47.);
let p_4 = Point::<f64>::new(9., 48.);
let b_2 = p_3.bearing(p_4);
assert_relative_eq!(b_2, 0., epsilon = 1.0e-6);
}
}