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use num_traits::{Float, FromPrimitive};
use types::Point;
pub trait HaversineDestination<T: Float> {
fn haversine_destination(&self, bearing: T, distance: T) -> Point<T>;
}
impl<T> HaversineDestination<T> for Point<T>
where
T: Float + FromPrimitive,
{
fn haversine_destination(&self, bearing: T, distance: T) -> Point<T> {
let center_lng = self.x().to_radians();
let center_lat = self.y().to_radians();
let bearing_rad = bearing.to_radians();
let rad = distance / T::from(6371000.0).unwrap();
let lat = { center_lat.sin() * rad.cos() + center_lat.cos() * rad.sin() * bearing_rad.cos() }.asin();
let lng = { bearing_rad.sin() * rad.sin() * center_lat.cos() }
.atan2(rad.cos() - center_lat.sin() * lat.sin()) + center_lng;
Point::new(lng.to_degrees(), lat.to_degrees())
}
}
#[cfg(test)]
mod test {
use super::*;
use algorithm::haversine_distance::HaversineDistance;
use num_traits::pow;
#[test]
fn returns_a_new_point() {
let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
let p_2 = p_1.haversine_destination(45., 10000.);
assert_eq!(p_2, Point::<f64>::new(9.274410083250379, 48.84033282787534));
let distance = p_1.haversine_distance(&p_2);
assert_relative_eq!(distance, 10000., epsilon = 1.0e-6)
}
#[test]
fn direct_and_indirect_destinations_are_close() {
let p_1 = Point::<f64>::new(9.177789688110352, 48.776781529534965);
let p_2 = p_1.haversine_destination(45., 10000.);
let square_edge = { pow(10000., 2) / 2. }.sqrt();
let p_3 = p_1.haversine_destination(0., square_edge);
let p_4 = p_3.haversine_destination(90., square_edge);
assert_relative_eq!(p_4.x(), p_2.x(), epsilon = 1.0e-6);
assert_relative_eq!(p_4.y(), p_2.y(), epsilon = 1.0e-6);
}
}