Unify line measures

All of these algorithm implementations already existed, but I'm
proposing a new way to organize them which I hope will be more
consistent and discoverable.

Note: The new Haversine::bearing and Geodesic::bearing return 0..360,
the legacy traits HaversineBearing and GeodesicBearing returned
-180..180

Additional changes:

Deleted the deprecated `Bearing` trait which was previously superceeded
by the unambiguous `HaversineBearing` trait, but now is re-defined as
`Haversine::bearing`

= Future Work =

In an effort to minimize this PR, while keeping the change reasonably
coherent, I've left some things out

== Methods on Euclidean ==
 -[ ] bearing (doesn't currently exist)
 -[ ] destination (doesn't currently exist)
 -[ ] intermediate (exists, but InterpolatePoint trait also needs intermediate_fill)
 -[ ] intermediate_fill (doesn't currently exist)

== Deprecate Legacy Traits ==
 -[ ] Deprecate Legacy impls
 -[ ] Switcheroo the actual implementation: move the actual implementation to the new traits, and have the legacy traits delegate to the new traits.
 -[ ] Move over any tests from the legacy implementation to the new home

== Methods on Geoms (Future PR) ==
 -[ ] Length
     -[ ] Haversine
     -[ ] Rhumb
     -[ ] Geodesic
     -[ ] Euclidean
 -[ ] Densify
     -[ ] Haversine
     -[ ] Rhumb
     -[ ] Geodesic
     -[ ] Euclidean

FIXES #1210
FIXES #1181

geo/src/algorithm/geodesic_intermediate.rs

@@ -2,7 +2,6 @@ use crate::{CoordFloat, Point};
 use geographiclib_rs::{DirectGeodesic, Geodesic, InverseGeodesic};
 
 /// Returns a new Point along a route between two existing points on an ellipsoidal model of the earth
-
 pub trait GeodesicIntermediate<T: CoordFloat> {
     /// Returns a new Point along a route between two existing points on an ellipsoidal model of the earth
     ///
@@ -25,7 +24,6 @@ pub trait GeodesicIntermediate<T: CoordFloat> {
     /// assert_relative_eq!(i50, i50_should, epsilon = 1.0e-6);
     /// assert_relative_eq!(i80, i80_should, epsilon = 1.0e-6);
     /// ```
-
     fn geodesic_intermediate(&self, other: &Point<T>, f: T) -> Point<T>;
     fn geodesic_intermediate_fill(
         &self,

geo/src/algorithm/line_measures/bearing.rs

@@ -0,0 +1,13 @@
+use geo_types::{CoordFloat, Point};
+
+/// Calculate the bearing between two points
+pub trait Bearing<F: CoordFloat> {
+    /// Calculate the bearing from `origin` to `destination` in degrees.
+    ///
+    /// See [specific implementations](#implementors) for details.
+    ///
+    /// # Units
+    /// - `origin`, `destination`: Point where the units of x/y depend on the [trait implementation](#implementors).
+    /// - returns: degrees, where: North: 0°, East: 90°, South: 180°, West: 270°
+    fn bearing(origin: Point<F>, destination: Point<F>) -> F;
+}

geo/src/algorithm/line_measures/destination.rs

@@ -0,0 +1,19 @@
+use geo_types::{CoordFloat, Point};
+
+/// Calculate the destination point from an origin point, a bearing and a distance.
+pub trait Destination<F: CoordFloat> {
+    /// Returns a new point having travelled the `distance` along a line
+    /// from the `origin` point with the given `bearing`.
+    ///
+    /// See [specific implementations](#implementors) for details.
+    ///
+    /// # Units
+    ///
+    /// - `origin`: Point where the units of x/y depend on the [trait implementation](#implementors).
+    /// - `bearing`: degrees, where: North: 0°, East: 90°, South: 180°, West: 270°
+    /// - `distance`: depends on the [trait implementation](#implementors).
+    /// - returns: Point where the units of x/y depend on the [trait implementation](#implementors).
+    ///
+    /// [`metric_spaces`]: super::metric_spaces
+    fn destination(origin: Point<F>, bearing: F, distance: F) -> Point<F>;
+}

geo/src/algorithm/line_measures/distance.rs

@@ -0,0 +1,12 @@
+/// Calculate the distance between the `Origin` and `Destination` geometry.
+pub trait Distance<F, Origin, Destination> {
+    /// Note that not all implementations support all geometry combinations, but at least `Point` to `Point`
+    /// is supported.
+    /// See [specific implementations](#implementors) for details.
+    ///
+    /// # Units
+    ///
+    /// - `origin`, `destination`: geometry where the units of x/y depend on the trait implementation.
+    /// - returns: depends on the trait implementation.
+    fn distance(origin: Origin, destination: Destination) -> F;
+}

geo/src/algorithm/line_measures/interpolate_point.rs

@@ -0,0 +1,34 @@
+use crate::{CoordFloat, Point};
+
+// REVIEW: Naming alternatives:
+// - LinearReferencing
+// - PointAlongLine
+// - LineInterpolatePoint (postgis)
+// - Interpolate (shapely)
+// - Position (geographiclib)
+// - Intermediate (georust::geo)
+pub trait InterpolatePoint<F: CoordFloat> {
+    /// Returns a new Point along a line between two existing points
+    ///
+    /// See [specific implementations](#implementors) for details.
+    fn point_at_ratio_between(start: Point<F>, end: Point<F>, ratio_from_start: F) -> Point<F>;
+
+    // TODO:
+    // fn point_at_distance_between(start: Point<F>, end: Point<F>, distance_from_start: F) -> Point<F>;
+
+    /// Interpolates `Point`s along a line between `start` and `end`.
+    ///
+    /// See [specific implementations](#implementors) for details.
+    ///
+    /// As many points as necessary will be added such that the distance between points
+    /// never exceeds `max_distance`. If the distance between start and end is less than
+    /// `max_distance`, no additional points will be included in the output.
+    ///
+    /// `include_ends`: Should the start and end points be included in the output?
+    fn points_along_line(
+        start: Point<F>,
+        end: Point<F>,
+        max_distance: F,
+        include_ends: bool,
+    ) -> impl Iterator<Item = Point<F>>;
+}

geo/src/algorithm/line_measures/metric_spaces/euclidean.rs

@@ -0,0 +1,71 @@
+use super::super::Distance;
+use crate::{GeoFloat, Point};
+
+/// Euclidean space measures distance with the pythagorean formula - what you'd measure with a ruler.
+///
+/// You must use projected coordinates with Euclidean space —
+/// for lon/lat points, use the [`Haversine`], [`Geodesic`], or other [metric spaces].
+///
+/// [`Haversine`]: super::Haversine
+/// [`Geodesic`]: super::Geodesic
+/// [metric spaces]: super
+pub struct Euclidean;
+
+/// Calculate the Euclidean distance (a.k.a. pythagorean distance) between two Points
+impl<F: GeoFloat> Distance<F, Point<F>, Point<F>> for Euclidean {
+    /// Calculate the Euclidean distance (a.k.a. pythagorean distance) between two Points
+    ///
+    /// # Units
+    /// - `origin`, `destination`: Point where the units of x/y represent non-angular units
+    ///    — e.g. meters or miles, not lon/lat. For lon/lat points, use the
+    ///    [`Haversine`] or [`Geodesic`] [metric spaces].
+    /// - returns: distance in the same units as the `origin` and `destination` points
+    ///
+    /// # Example
+    /// ```
+    /// use geo::{Euclidean, Distance};
+    /// use geo::Point;
+    /// // web mercator
+    /// let new_york_city = Point::new(-8238310.24, 4942194.78);
+    /// // web mercator
+    /// let london = Point::new(-14226.63, 6678077.70);
+    /// let distance: f64 = Euclidean::distance(new_york_city, london);
+    ///
+    /// assert_eq!(
+    ///     8_405_286., // meters in web mercator
+    ///     distance.round()
+    /// );
+    /// ```
+    ///
+    /// [`Haversine`]: super::Haversine
+    /// [`Geodesic`]: super::Geodesic
+    /// [metric spaces]: super
+    fn distance(origin: Point<F>, destination: Point<F>) -> F {
+        crate::EuclideanDistance::euclidean_distance(&origin, &destination)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    type MetricSpace = Euclidean;
+
+    mod distance {
+        use super::*;
+
+        #[test]
+        fn new_york_to_london() {
+            // web mercator
+            let new_york_city = Point::new(-8238310.24, 4942194.78);
+            // web mercator
+            let london = Point::new(-14226.63, 6678077.70);
+            let distance: f64 = MetricSpace::distance(new_york_city, london);
+
+            assert_relative_eq!(
+                8_405_286., // meters in web mercator
+                distance.round()
+            );
+        }
+    }
+}