how to calculate angle between two path lines on google map using lat-long coordinates

Question

I want to calculate angle between two path lines on Google map. I have the lat-long coordinates of the end points of the lines. Please suggest If there is other information I can use to do this that is available from Google maps.

Answer 1

If the distances are small you can use this method. The accuracy reduces with large distances and the further you move from the equator. First find bearings with computeHeading()

computeHeading(from:LatLng, to:LatLng) .Returns the heading from one LatLng to another LatLng. Headings are expressed in degrees clockwise from North within the range [-180,180).

function getBearings(){
    var spherical = google.maps.geometry.spherical; 
    var point1 = markers[0].getPosition();// latlng of point1
    var point2 = markers[1].getPosition();
    var point3 = markers[2].getPosition();
    var bearing1 = google.maps.geometry.spherical.computeHeading(point1,point2);
    var bearing2 = google.maps.geometry.spherical.computeHeading(point2,point3);
    var angle =getDifference(bearing1, bearing2);
    return angle;
}

You can then use this function to calculate angle between the bearings.

function getDifference(a1, a2) {
    al = (a1>0) ? a1 : 360+a1;
    a2 = (a2>0) ? a2 : 360+a2;
    var angle = Math.abs(a1-a2)+180;
    if (angle > 180){
        angle = 360 - angle;
    }
   return   Math.abs(angle);
}

Answer 2

Calculate both bearings using an API you have. Then write a function angleDiff(angle1, angle2).

There are two possible angleDiff types: One that retunrs negative angles, too. And one that only delivers positive angles.

Test that function with these test cases:

angleDiff(350, 10): diff = 20
10, 350: diff = 20 (or -20)

170, 190 :diff = 20
190, 170: diff 20 (or -20)

0,360 and 360,0: diff = 0