Distance calculation gives strange output javascript

Question

I need to calculate the distance between two latitude and longitude points. I found this javascript code which I suppose I want. Here comes the problem. I add the two positions lat and lng values in, and sometimes it just gives random output. What happens is two points literally next to other are sometimes like 8000 meters away, but two other much furthest points return only 1500 meters for example.

function degreesToRadians(degrees) {
    return degrees * Math.PI / 180;
  }
  
  function getDistanceFromLatLonInKm(lat1,lon1,lat2,lon2) {
    var R = 6371; // Radius of the earth in km
    var dLat = deg2rad(lat2-lat1);  // deg2rad below
    var dLon = deg2rad(lon2-lon1); 
    var a = 
      Math.sin(dLat/2) * Math.sin(dLat/2) +
      Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * 
      Math.sin(dLon/2) * Math.sin(dLon/2)
      ; 
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
    var d = R * c; // Distance in km
    return d;
  }
  
  function deg2rad(deg) {
    return deg * (Math.PI/180)
  }
const distanceR = getDistanceFromLatLonInKm(userLat, userLng, solLat, solLng)

---

Lat: 68.00757101804007, lng: -49.306640625 

to

lat: 73.26312194058698 lng: -23.535461425781254

is 1143 kilometres, but these two points are next to each other.

lat: 66.75724984139227, lng: -16.259765625000004 

to

lat: 71.99597405683693 lng:-42.31933593750001

is 1161 metres and the points are much farther then the previus one. Here I think it calculates fine, unlike the two previous lat and lng points.

Answer 1

I've tested the examples you provided and did a few on my own and I believe your implementation is working fine. I did however get different results using your examples and code.

The first example returns approx. 1102km, which seems close to the distance using a visualizer. The second example returns 1161 kilometres which visualized again seems about right. Please note: the images in the links were constructed using gpsvisualizer.com which uses a Vincenty formula to calculate distance, hence the slight variation in distance numbers.

function getDistanceFromLatLonInKm(lat1, lon1, lat2, lon2) {
  var R = 6371; // Radius of the earth in km
  var dLat = deg2rad(lat2 - lat1); // deg2rad below
  var dLon = deg2rad(lon2 - lon1);
  var a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c; // Distance in km
  return d;
}

function deg2rad(deg) {
  return deg * (Math.PI / 180)
}

const e1 = {
  lat1: 68.00757101804007,
  lon1: -49.306640625,
  lat2: 73.26312194058698,
  lon2: -23.535461425781254
}
const e2 = {
  lat1: 66.75724984139227,
  lon1: -16.259765625000004,
  lat2: 71.99597405683693,
  lon2: -42.31933593750001
}

const dist1 = getDistanceFromLatLonInKm(e1.lat1, e1.lon1, e1.lat2, e1.lon2);
const dist2 = getDistanceFromLatLonInKm(e2.lat1, e2.lon1, e2.lat2, e2.lon2);
console.log(`Example 1 distance: ${dist1}km. Example 2 distance: ${dist2}km`);

I can not reproduce the issue you are having so I believe your error lies in your visualization of coordinates.