get Angle method to get a simplistic degree bearing for plotting moti…

src/getAngle.test.js

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+import getAngle from './getAngle';
+
+describe('getRhumbLineBearing is not the same as Angle', () => {
+    it('should return a bearing between two points in degrees', () => {
+        expect(
+            getAngle(
+                { latitude: 39.778889, longitude: -104.9825 },
+                { latitude: 43.778889, longitude: -102.9825 }
+            )
+        ).not.toEqual(20.438617005368314); // will return 19
+    });
+});
+
+describe('getAngle is not the same as Angle', () => {
+    it('should return a bearing between two points in degrees', () => {
+        expect(
+            getAngle(
+                { latitude: -2.584148, longitude: -44.243597 },
+                { latitude: -2.584136, longitude: -44.243574 }
+            )
+        ).toEqual(62);
+    });
+});

src/getAngle.ts

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+import getLatitude from './getLatitude';
+import getLongitude from './getLongitude';
+import { GeolibInputCoordinates } from './types';
+
+// Converts from degrees to radians.
+function toRadians(degrees) {
+  return degrees * Math.PI / 180;
+};
+// Converts from radians to degrees.
+function toDegrees(radians) {
+  return radians * 180 / Math.PI;
+};
+
+// Calculates the angle based on the line of two points.
+const getAngle = (
+    from: GeolibInputCoordinates,
+    to: GeolibInputCoordinates,
+    accuracy: number = 1
+) => {
+
+    const fromLat = toRadians(getLatitude(from));
+    const fromLon = toRadians(getLongitude(from));
+    const toLat   = toRadians(getLatitude(to));
+    const toLon   = toRadians(getLongitude(to));
+
+    let y = Math.sin(toLon - fromLon) * Math.cos(toLat);
+    let x = Math.cos(fromLat) * Math.sin(toLat) -
+          Math.sin(fromLat) * Math.cos(toLat) * Math.cos(toLon - fromLon);
+    let bearing = Math.atan2(y, x);
+    bearing = toDegrees(bearing);
+    bearing = (bearing + 360) % 360;
+    return parseInt(bearing || 0);
+
+};
+
+export default getAngle;