Flutter : Calculate destination point from current location and bearing

Question

I'm looking to draw a line on a map from current user position with his bearing/heading. But the line always have the same direction even if I rotate the phone to another direction. I wonder if I miss something in my calculation.

final la1 = userPosition.latitude;
final lo1 = userPosition.longitude;

const r = 6367; // earth radius
const d = 40; // distance
const dist = d / r;

final bearing = vector.radians(direction.value);

final la2 =
        asin(sin(la1) * cos(dist) + cos(la1) * sin(dist) * cos(bearing));
final lo2 = lo1 +
        atan2(sin(bearing) * sin(dist) * cos(la1),
            cos(dist) - sin(la1) * sin(la2));


return LatLng(la2, lo2);

As you can see in the screenshots bellow, I create 2 lines with a different bearing (check map orientation), but they look the same.

Answer 1

import 'dart:math';

import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:vector_math/vector_math.dart';

LatLng createCoord(LatLng coord, double bearing, double distance) {
  var radius = 6371e3; //meters
  var delta = (distance) / radius; // angular distance in radians
  var teta = radians(bearing);
  var phi1 = radians(coord.longitude);
  var lambda1 = radians(coord.latitude);

  var phi2 = asin(sin(phi1) * cos(delta) + cos(phi1) * sin(delta) * cos(teta));

  var lambda2 = lambda1 +
      atan2(sin(teta) * sin(delta) * cos(phi1),
          cos(delta) - sin(phi1) * sin(phi2));

  lambda2 = (lambda2 + 3 * pi) % (2 * pi) - pi; // normalise to -180..+180°

  return LatLng(degrees(lambda2), degrees(phi2)); //[lon, lat]
}