Proof of concept: Allow custom earth radii

geo/src/algorithm/rhumb/distance.rs

@@ -1,4 +1,4 @@
-use crate::{CoordFloat, Point, MEAN_EARTH_RADIUS};
+use crate::{earth_radius::{MeanEarthRadius, Iugg}, CoordFloat, Point};
 use num_traits::FromPrimitive;
 
 use super::RhumbCalculations;
@@ -7,7 +7,7 @@ use super::RhumbCalculations;
 ///
 /// [rhumb line]: https://en.wikipedia.org/wiki/Rhumb_line
 ///
-/// *Note*: this implementation uses a mean earth radius of 6371.088 km, based on the [recommendation of
+/// *Note*: this implementation defaults to a mean earth radius of 6371.088 km, based on the [recommendation of
 /// the IUGG](ftp://athena.fsv.cvut.cz/ZFG/grs80-Moritz.pdf)
 pub trait RhumbDistance<T, Rhs = Self> {
     /// Determine the distance between along the [rhumb line] between two geometries.
@@ -37,16 +37,20 @@ pub trait RhumbDistance<T, Rhs = Self> {
     /// ```
     ///
     /// [rhumb line]: https://en.wikipedia.org/wiki/Rhumb_line
-    fn rhumb_distance(&self, rhs: &Rhs) -> T;
+    fn rhumb_distance(&self, rhs: &Rhs) -> T {
+        self.rhumb_distance_with_radius::<Iugg>(rhs)
+    }
+
+    fn rhumb_distance_with_radius<Radius: MeanEarthRadius>(&self, rhs: &Rhs) -> T;
 }
 
 impl<T> RhumbDistance<T, Point<T>> for Point<T>
 where
     T: CoordFloat + FromPrimitive,
 {
-    fn rhumb_distance(&self, rhs: &Point<T>) -> T {
+    fn rhumb_distance_with_radius<Radius: MeanEarthRadius>(&self, rhs: &Point<T>) -> T {
         let calculations = RhumbCalculations::new(self, rhs);
-        calculations.delta() * T::from(MEAN_EARTH_RADIUS).unwrap()
+        calculations.delta() * Radius::value()
     }
 }
 

geo/src/earth_radius.rs

@@ -0,0 +1,57 @@
+use crate::CoordNum;
+use num_traits::FromPrimitive;
+
+/// Trait representing different mean earth radii
+pub trait MeanEarthRadius {
+    const VALUE: f64;
+
+    fn value<T: CoordNum + FromPrimitive>() -> T {
+        T::from(Self::VALUE).unwrap()
+    }
+}
+
+/// Represents the WGS84 mean earth radius.
+///
+/// The WGS84 (World Geodetic System 1984) is a standard for use in cartography, geodesy, and satellite navigation.
+/// The mean earth radius for WGS84 is approximately 6378137.0 meters.
+pub struct Wgs84;
+
+/// Represents the GRS80 mean earth radius.
+///
+/// The GRS80 (Geodetic Reference System 1980) is a geodetic reference system consisting of a global reference ellipsoid and a gravity field model.
+/// The mean earth radius for GRS80 is approximately 6378137.0 meters.
+pub struct Grs80;
+
+/// Represents the mean earth radius as recommended by the IUGG.
+///
+/// The mean earth radius for this model is approximately 6371008.8 meters.
+/// This value is recommended by the IUGG:
+/// Moritz, H. (2000). Geodetic Reference System 1980. Journal of Geodesy, 74(1), 128–133. doi:10.1007/s001900050278
+/// "Derived Geometric Constants: mean radius" (p133)
+/// https://link.springer.com/article/10.1007/s001900050278
+/// https://sci-hub.se/https://doi.org/10.1007/s001900050278
+/// https://en.wikipedia.org/wiki/Earth_radius#Mean_radius
+pub struct Iugg;
+
+/// Represents a spherical mean earth radius.
+///
+/// This is a simplified model assuming the Earth is a perfect sphere.
+/// The mean earth radius for a sphere is approximately 6371000.0 meters.
+/// This value is commonly used in various scientific, educational, and engineering contexts for simplicity.
+pub struct Sphere;
+
+impl MeanEarthRadius for Wgs84 {
+    const VALUE: f64 = 6378137.0;
+}
+
+impl MeanEarthRadius for Grs80 {
+    const VALUE: f64 = 6378137.0;
+}
+
+impl MeanEarthRadius for Iugg {
+    const VALUE: f64 = 6371008.8;
+}
+
+impl MeanEarthRadius for Sphere {
+    const VALUE: f64 = 6371000.0;
+}

geo/src/lib.rs

@@ -236,13 +236,17 @@ mod utils;
 use crate::kernels::{RobustKernel, SimpleKernel};
 pub(crate) use geometry_cow::GeometryCow;
 
+pub mod earth_radius;
+
 #[cfg(test)]
 #[macro_use]
 extern crate approx;
 
 #[macro_use]
 extern crate log;
 
+// TODO: remove below?
+
 /// Mean radius of Earth in meters
 /// This is the value recommended by the IUGG:
 /// Moritz, H. (2000). Geodetic Reference System 1980. Journal of Geodesy, 74(1), 128–133. doi:10.1007/s001900050278