cheap-ruler-rs

Port to safe Rust of cheap-ruler and cheap-ruler-cpp, a collection of very fast approximations to common geodesic measurements.

The approximations are based on WGS84 and its ellipsoidal model of the Earth. The results of calculations are accurate to small differences of the latitude provided at construction, and are less computationally expensive.

See cheap-ruler's readme for accuracy claims compared to the Vincenty formulas.

Usage

Here's example program to print the distance and bearing between two points:

extern crate cheap_ruler;
#[macro_use] extern crate geo_types;

use cheap_ruler::{CheapRuler, DistanceUnit};

fn main() {
  let ruler = CheapRuler::new(44.7192003, DistanceUnit::Meters);
  let p1 = point!(x: 14.8901816, y: 44.7209699);
  let p2 = point!(x: 14.8905188, y: 44.7209699);

  let dist = ruler.distance(&p1, &p2);
  let bearing = ruler.bearing(&p1, &p2);

  println!("Distance between points: {}", dist);
  println!("Bearing: {}", bearing);
}

Unit of distance

This Rust port additionally allows the distance unit of the ruler to be changed and retrieved at any point after construction at the cost of larger memory size of the ruler struct itself (40 bytes instead of 16 bytes), but with no additional overhead.

extern crate cheap_ruler;
use cheap_ruler::{CheapRuler, DistanceUnit};

fn main() {
  let mut ruler = CheapRuler::new(44.7192003, DistanceUnit::Meters);
  println!("Distance unit: {:?}", ruler.distance_unit());

  ruler.change_unit(DistanceUnit::Miles);
  println!("Distance unit: {:?}", ruler.distance_unit());
}

geo_types

The library uses the geo-types crate for representation of points and coordinates. The one exception are the BBox functions, which use a custom Rect implementation that does not automatically swap min/max bounds:

extern crate cheap_ruler;
#[macro_use] extern crate geo_types;

use cheap_ruler::{CheapRuler, DistanceUnit, Rect};
use geo_types::{Coordinate};

fn main() {
  let ruler = CheapRuler::new(32.8351, DistanceUnit::Kilometers);
  let bbox = Rect::new(
      Coordinate { x: 179.9, y: 32.7 },
      Coordinate { x: -179.9, y: 32.9 },
  );
  let p = point!(x: 180.0, y: 32.8);
  assert!(ruler.inside_bbox(&p, &bbox));
}

Benchmarks

Cheap ruler's distance calculation is about 16 times faster than the geo crate's haversine algorithm implementation (times below are from a machine with Intel Core i7-8550U).

distance/cheap_ruler    time:   [291.10 ps 292.38 ps 293.89 ps]
distance/haversine      time:   [4.7215 ns 4.8545 ns 5.0086 ns]
distance/vincenty       time:   [315.83 ns 320.75 ns 325.93 ns]

Changelog

See the CHANGELOG file for details.

License

This library is licensed under the ISC License. See the LICENSE file for the full license content.

TODO

• Use idiomatic Rust for methods that follow C++ conventions.