How to Calculate Total Distance From LatLng List In Flutter?

• General

When we use flutter and the ‘package:latlong/latlong.dart‘ to parse a GPX file into a list of LatLng objects. So Lets take a dive into learning how to Calculate Total Distance From LatLng List In Flutter.

How to Calculate Total Distance From LatLng List In Flutter?

You can do a loop and find the total distance by using 2 points each time. Here are some added random dummy data to show how it works.

import 'dart:math' show cos, sqrt, asin;

void main() {
  double calculateDistance(lat1, lon1, lat2, lon2){
    var p = 0.017453292519943295;
    var c = cos;
    var a = 0.5 - c((lat2 - lat1) * p)/2 + 
          c(lat1 * p) * c(lat2 * p) * 
          (1 - c((lon2 - lon1) * p))/2;
    return 12742 * asin(sqrt(a));
  }

  List<dynamic> data = [
    {
      "lat": 44.968046,
      "lng": -94.420307
    },{
      "lat": 44.33328,
      "lng": -89.132008
    },{
      "lat": 33.755787,
      "lng": -116.359998
    },{
      "lat": 33.844843,
      "lng": -116.54911
    },{
      "lat": 44.92057,
      "lng": -93.44786
    },{
      "lat": 44.240309,
      "lng": -91.493619
    },{
      "lat": 44.968041,
      "lng": -94.419696
    },{
      "lat": 44.333304,
      "lng": -89.132027
    },{
      "lat": 33.755783,
      "lng": -116.360066
    },{
      "lat": 33.844847,
      "lng": -116.549069
    },
  ];
  double totalDistance = 0;
  for(var i = 0; i < data.length-1; i++){
    totalDistance += calculateDistance(data[i]["lat"], data[i]["lng"], data[i+1]["lat"], data[i+1]["lng"]);
  }
  print(totalDistance);
}

This function calculates the distance between two points. You can also try with the below code snippet:

unit = the unit you desire for results              
      where: 'M' is statute miles (default) 
             'K' is kilometers            
             'N' is nautical miles
String distance(
          double lat1, double lon1, double lat2, double lon2, String unit) {
         double theta = lon1 - lon2;
         double dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) +
         cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta));
         dist = acos(dist);
         dist = rad2deg(dist);
         dist = dist * 60 * 1.1515;
          if (unit == 'K') {
            dist = dist * 1.609344;
          } else if (unit == 'N') {
            dist = dist * 0.8684;
          }
          return dist.toStringAsFixed(2);
        }

    double deg2rad(double deg) {
      return (deg * pi / 180.0);
    }

    double rad2deg(double rad) {
      return (rad * 180.0 / pi);
    }

    void main() {
      print("Distance : " + distance(32.9697, -96.80322, 29.46786, -98.53506, 'K'));
    }

Use the library latlong for common latitude and longitude calculation. This supports both, the “Haversine” and the “Vincenty” algorithm.

List<dynamic> data = [
    {
        "lat": 44.968046,
        "lng": -94.420307
    },
    ...
];


final Distance distance = Distance();
double totalDistanceInM = 0;
double totalDistanceInKm = 0;

for(var i = 0; i < data.length - 1; i++){
    totalDistanceInM += distance(
        LatLng(data[i]["lat"], data[i]["lng"]),
        LatLng(data[i+1]["lat"], data[i+1]["lng"])
    );

    totalDistanceInKm += distance.as(
        LengthUnit.Kilometer, 
        LatLng(data[i]["lat"], data[i]["lng"]), 
        LatLng(data[i+1]["lat"], data[i+1]["lng"]),
    );
}

You can also geolocator plugin for the same.

Geolocator.distanceBetween(lat1, lon1, lat2, lon2);

I’ve used the vector_math for converting degree to radians and also the geolocator for getting the current user latitude and longitude.

If in case searching from the current location also there is a method wherein you can calculate the distance between two locations directly as Geolocator.distanceBetween startLatitude, startLongitude, endLatitude, endLongitude.

import 'dart:math' show sin, cos, sqrt, atan2;
import 'package:vector_math/vector_math.dart';
import 'package:geolocator/geolocator.dart';

Position _currentPosition;
double earthRadius = 6371000; 

//Using pLat and pLng as dummy location
double pLat = 22.8965265;   double pLng = 76.2545445; 


//Use Geolocator to find the current location(latitude & longitude)
getUserLocation() async {
   _currentPosition = await GeoLocator.getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
}

//Calculating the distance between two points without Geolocator plugin
getDistance(){
   var dLat = radians(pLat - _currentPosition.latitude);
   var dLng = radians(pLng - _currentPosition.longitude);
   var a = sin(dLat/2) * sin(dLat/2) + cos(radians(_currentPosition.latitude)) 
           * cos(radians(pLat)) * sin(dLng/2) * sin(dLng/2);
   var c = 2 * atan2(sqrt(a), sqrt(1-a));
   var d = earthRadius * c;
   print(d); //d is the distance in meters
}

//Calculating the distance between two points with Geolocator plugin
getDistance(){
   final double distance = Geolocator.distanceBetween(pLat, pLng, 
           _currentPosition.latitude, _currentPosition.longitude); 
   print(distance);
}

Conclusion:

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Written by Nirali Patel

Nirali Patel is a dedicated Flutter developer with over two years of experience, specializing in creating seamless mobile applications using Dart. With a passion for crafting user-centric solutions, Nirali combines technical proficiency with innovative thinking to push the boundaries of mobile app development.