Direction between two locations

Former Member over 9 years ago

Hello together, I'm currently trying to calculate the direction from one point to another. What I found so far is this formula:

var y = Math.sin(&#955;2-&#955;1) * Math.cos(&#966;2);

var x = Math.cos(&#966;1)*Math.sin(&#966;2) -

        Math.sin(&#966;1)*Math.cos(&#966;2)*Math.cos(&#955;2-&#955;1);

var brng = Math.atan2(y, x).toDegrees();

This is my Monkey C implementation:

function getBearing(oldPos, newPos)

    {

    	var lat1 = oldPos.toRadians()[0];

		var lat2 = newPos.toRadians()[0];

		var lon1 = oldPos.toRadians()[1];

		var lon2 = newPos.toRadians()[1];

    	var y = Math.sin(lon2 - lon1) * Math.cos(lat2);

    	var x = Math.cos(lat1) * Math.sin(lat2) -

    			Math.sin(lat1) * Math.cos(lat2) * Math.cos(lon2 - lon1);

    	return atan2(y,x);

    }

I call this with the two positions I want to calculate the direction from like this:

bearing = toDegrees(getBearing(oldPosition, newPosition));

These are my helper functions:

function toDegrees(radian)

    {

    	var degree = radian * 180 / Math.PI;

    	

    	if(degree < 0)

    	{

    		degree = 180 + (180 + degree);

    	}

    	

    	return degree;

    }



function atan2(y,x)

	{

	    var angle = 0;

	    if (x == 0)

	    {

	        if (y == 0)

	        {

	            angle = 0;

	        }

	        else if (y > 0)

	        {

	            angle = Math.PI/2;

	        }

	        else

	        {

	            angle = -Math.PI/2;

	        }

	    }

	    else

	    {

	        angle = Math.atan(y/x);

	        if (x < 0)

	        {

	            if (y > 0)

	            {

	                angle += Math.PI;

	            }

	            else if (y < 0)

	            {

	                angle -= Math.PI;

	            }

	            else

	            {

	                angle = Math.PI;

	            }

	        }

	    }

	    return angle;

	}

What I want to see is the direction in degrees from the new Position to the old position. I'm not sure what exactly is wrong here but the result is definately not correct. I'm getting a value in degrees, but it can't be correct. Any help would be appreciated. Thanks in advance.

/Romano

travis.vitek over 9 years ago

I have code to do this in my Compass App/Widget. If nobody has found your problem by the time I get home from work, I'll post the code.

Former Member over 9 years ago

I have code to do this in my Compass App/Widget. If nobody has found your problem by the time I get home from work, I'll post the code.

HI Travis, I've solved the problem. It Was a missmatch in the two positions. Works flawless now. Thank you.

powerlord over 9 years ago

Hi, can you post your code now it is working please?

I've got the following, which is coming up with totally different bearings from your code - and you didn't post the fix you said you'd found:

function computeBearing(pos1, pos2){
var la1 = pos1.toDegrees()[0];
var lo1 = pos1.toDegrees()[1];
var la2 = pos2.toDegrees()[0];
var lo2 = pos2.toDegrees()[1];

var y = Math.sin(toRadians(lo2-lo1)) * Math.cos(toRadians(la2));
var x = Math.cos(toRadians(la1))*Math.sin(toRadians(la2)) - Math.sin(toRadians(la1))*Math.cos(toRadians(la2))*Math.cos(toRadians(lo2-lo1));
var bearing = atan2(y, x);
bearing = bearing * 180 / Math.PI;
bearingToStart = bearing;
}

function atan2(y,x)
{
var angle = 0;
if (x == 0)
{
if (y == 0)
{
angle = 0;
}
else if (y > 0)
{
angle = Math.PI/2;
}
else
{
angle = -Math.PI/2;
}
}
else
{
angle = Math.atan(y/x);
if (x < 0)
{
if (y > 0)
{
angle += Math.PI;
}
else if (y < 0)
{
angle -= Math.PI;
}
else
{
angle = Math.PI;
}
}
}
return angle;
}