Bearing ange from 2 GPS coordinates

Hello all,

I'm trying to find the bearing\azimuth (an angle from North to the object) from 2 GPS coordinates I have (the first one is my target's coordinate and the second is my own coordinates).

Then I'm planning to draw a marker with this angle on my compass bar on the screen. I think to draw that with GUI.Label.

I've found the following topic :

http://answers.unity3d.com/questions/908877/get-azimuth-from-relative-direction.html and the following line(c#):

var azimuth : float = Mathf.Atan2(direction.x, direction.z)*Mathf.Rad2Deg

Why this line has this?

*Mathf.Rad2Deg

Here I've also found the formula to calculate the bearing\azimuth:

http://www.igismap.com/formula-to-find-bearing-or-heading-angle-between-two-points-latitude-longitude/

Bearing\azimuth from point A to B, can be calculated as,

β = atan2(X,Y),

where, X and Y are two quantities and can be calculated as:

(1) X = cos θb * sin ∆L

(2) Y = cos θa sin θb – sin θa cos θb * cos ∆L

‘L’ is the longitude, ‘θ’ is the latitude,

1) So, is this

*Mathf.Rad2Deg

needed?

2) How to choose which point will be "a" and "b" for the formula((1) and (2)) above?