Merge georust#124

124: Added destination trait. r=frewsxcv The code is inspired from the turf.js equivalent fn in https://github.com/Turfjs/turf/tree/master/packages/turf-destination It basically shoots a ray on the sphere using a distance and an angle from an existing point to create a new point. This is useful when creating pseudo shapes like circles (split circle in _n_ angle angle slices, create _n_ new Points via `destination` from a circle center Point, then combine the new Points to a Polygon.
NolwennD · Jul 24, 2017 · 283fbbe · 283fbbe
2 parents f15f47b + 99306c9
commit 283fbbe
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diff --git a/src/algorithm/haversine_destination.rs b/src/algorithm/haversine_destination.rs
@@ -0,0 +1,57 @@
+use num_traits::{Float, FromPrimitive};
+use types::Point;
+
+/// Returns a new Point using the distance to the existing Point and a bearing for the direction
+
+pub trait HaversineDestination<T: Float> {
+    /// Returns a new Point using distance to the existing Point and a bearing for the direction
+    ///
+    /// ```
+    /// use geo::Point;
+    /// use geo::algorithm::haversine_destination::HaversineDestination;
+    ///
+    /// 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))
+    /// ```
+    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();
+
+        // WGS84 equatorial radius is 6378137.0
+        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;
+
+    #[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)
+    }
+}
diff --git a/src/algorithm/mod.rs b/src/algorithm/mod.rs
@@ -10,6 +10,8 @@ pub mod area;
 pub mod length;
 /// Returns the Euclidean distance between two geometries.
 pub mod distance;
+/// Returns a new Point using distance and bearing.
+pub mod haversine_destination;
 /// Returns the Haversine distance between two geometries.
 pub mod haversine_distance;
 /// Returns the Bbox of a geometry.
@@ -22,7 +24,7 @@ pub mod simplifyvw;
 pub mod convexhull;
 /// Orients a Polygon's exterior and interior rings.
 pub mod orient;
-/// Returns the extreme indices of a `Polygon`, `MultiPolygon`, or `MultiPoint`. 
+/// Returns the extreme indices of a `Polygon`, `MultiPolygon`, or `MultiPoint`.
 pub mod extremes;
 /// Rotates a geometry around either its centroid or a point by an angle, given in degrees.
 pub mod rotate;