/// Based on https://www.movable-type.co.uk/scripts/latlong.html

import "dart:math";

const double earthRadius = 6371;

/// Earth radius in kilometers

class Coordinates {

double latitude;

double longitude;

Coordinates(this.latitude, this.longitude);

}

double haversine(fi) => pow(sin(fi / 2), 2).toDouble();

/// Convert [angle] to radians

double radians(double angle) => (angle * pi) / 180;

/// Calculate distance from [p1] to [p2] in kilometers

/// We assume that earth is perfect sphere (which is not true)

/// In practice you might expect ~1% errors

double distance(Coordinates p1, Coordinates p2) {

double latitudeChange = radians(p2.latitude - p1.latitude);

double latitude1 = radians(p1.latitude);

double latitude2 = radians(p2.latitude);

double longitudeChange = radians(p2.longitude - p1.longitude);

double a =

haversine(latitudeChange) +

cos(latitude1) * cos(latitude2) * haversine(longitudeChange);

double c = 2 * atan2(sqrt(a), sqrt(1 - a));

return earthRadius * c;

}

void main() {

Coordinates newYork = new Coordinates(40.730610, -73.935242);

Coordinates moskov = new Coordinates(55.751244, 37.618423);

Coordinates toronto = new Coordinates(43.651070, -79.347015);

Coordinates seoul = new Coordinates(37.532600, 127.024612);

print("distance(newYork, moskov) = ${distance(newYork, moskov)}km");

print("distance(newYork, toronto) = ${distance(newYork, toronto)}km");

print("distance(seoul, moskov) = ${distance(seoul, moskov)}km");

print("distance(moskov, seoul) = ${distance(moskov, seoul)}km");

}