Calculating the distance between 2 points in c#

Question

I am trying to sort out a method to calculate the distance between 2 points in c#.

This is the code I have been trying though I fear the answer I get is not correct.

Answer 1

double lat1 = {};
double lat2 = {};
double lon1 = {};
double lon2 = {};

var R = 6376.5000; //Km
lat1 = lat1.ToRad();
lat2 = lat2.ToRad();
lon1 = lon1.ToRad();
lon2 = lon2.ToRad();
var dLat = lat2 - lat1;
var dLon = lon2 - lon1;
var a = Math.Pow(Math.Sin(dLat / 2), 2) + (Math.Pow(Math.Sin(dLon / 2), 2) * Math.Cos(lat1) * Math.Cos(lat2));
var c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
var distance = R * c;

public double ToRad(this double degs) {
    return degs * (Math.PI/180.0);
}

Input expects doubles.

This is the haversine formula, it's used to calculate the distances on our globe between two points. This is the distance in a straight line, if you need the distance on a path you will have to find all points on that path and then calculate the distances between each two points and then take the sum of that.