A dart helper to calculate the distance between two geometric points

distance.dart

import 'dart:math';

double calculateDifference(double lat1, double lon1, double lat2, double lon2) {
    double radius = 6371; // km
    double changeInLat = toRad(lat2 - lat1);
    double changeInLong = toRad(lon2 - lon1);
    double lat1Rad = toRad(lat1);
    double lat2Rad = toRad(lat2);

    double formula = sin(changeInLat / 2) * sin(changeInLat / 2) +
        sin(changeInLong / 2) *
            sin(changeInLong / 2) *
            cos(lat1Rad) *
            cos(lat2Rad);
    double c = 2 * atan2(sqrt(formula), sqrt(1 - formula));
    return radius * c;
  }