Mapping Math and Javascript

Question

After extensive research and fun learning about Google's mapping api, I am building a digital antenna map application. At this point, the next step in the project plan is to build a memory-map replication of the google map that is locating digital tv stations based upon input from the user's address. So, I am using this math code to formulate the bearing of the center of the google map and a lat/lng point from the database result set.

My question is: How can I complete the math to show the bearing in degrees?

this code is the math that returns the following array result set:

1.21  
1.10  
1.10  
1.10  
1.10  
2.62  
-0.29  
-1.17  
0.12  
3.04  

var y = Math.sin(longitude-center.lng()) * Math.cos(latitude);
var x = Math.cos(center.lat())*Math.sin(latitude) - Math.sin(center.lat())*Math.cos(latitude)*Math.cos(longitude-center.lng());
var bearing = (Math.atan2(y, x)).toFixed(2);

There seems to something missing in my calculations. The db table is holding the longitude values as a negative number to represent the upper western quadrant of the globe.

Any suggestions to complete my math would save a million nuerons, I've already burned a trillion.

Taking the degrees to radian suggestion, I've modified the javascript code:

 var radLat1 = center.lat() * Math.PI / 180;
 var radLat2 = latitude * Math.PI / 180;
 var radLng1 = center.lng() * Math.PI / 180;
 var radLng2 = longitude * Math.PI / 180;

 var y = Math.sin(radLng2- radLng1) * Math.cos(radLng2);
 var x = Math.cos(radLat1)*Math.sin(radLat2) -        Math.sin(radLat1)*Math.cos(radLat2)*Math.cos(radLng2-radLng1);
 var bearing = (Math.atan2(y, x)).toFixed(2);

url to testing project site: click here

the div at the bottom of the page is a result set returned from 2 arrays, the first holding the distance and second holding the bearing measurement.

Answer 1

Google maps returns coordinates in degrees. Of course, trig functions expect radians. So you'll want to convert to radians first:

function deg_to_rad(degrees) {
    return degrees * Math.PI / 180;
}

Your math looks like it's trying to do the the Haversine formula. I found a javascript implementation here for you to check your code against.

You can check your results against the FCC's DTV engineering maps.

Answer 2

With the help of Seth, and using my early morning brain (yes, I'm middle-aged and I am smarter in the morning).

The link to here, which I was studying, and Seth referred to, is the key. I used the code from the js file on the blog entry and morphed the code away from an oo javascript concept to a script running inline.

this is my solution:

var lat1 = center.lat();
var lon1 = center.lng();
var lat2 = latitude;
var lon2 = longitude;

lat1 = lat1 * Math.PI / 180;
lat2 = lat2 * Math.PI / 180;
var dLon = (lon2-lon1) * Math.PI / 180;
var y = Math.sin(dLon) * Math.cos(lat2);
var x = Math.cos(lat1)*Math.sin(lat2) - Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon);

var bearing = Math.atan2(y, x) * 180 / Math.PI;
    if (bearing < 0){
           bearing = bearing + 360;
    }

    bearing = bearing.toFixed(0);

stationDistance.push(distance.toFixed(1));
stationBearing.push(bearing);

I am running the demo google map here.

Thanks for the help and now I can move onto logic code that will recommend the correct product for my client's customer at this url.

stackoverflow ROCKS....

Robert