[SOLVED] Calculating the distance/bearing between two lat lon co ordinates

Calculating the distance/bearing between two lat lon co ordinates

I've been trying to work out the bearing between two lat lon co ordinates but am having trouble grasping the concept.

I have been to http://www.movable-type.co.uk/scripts/latlong.html and have been able to change to distance code to work with lua, however the bearing code in the paragraphs under has me a little confused.

local y = Math.sin(dLon) * Math.cos(lat2)
local x = Math.cos(lat1)*Math.sin(lat2) - Math.sin(lat1)*Math.cos(lat2)*Math.cos(dLon)
local brng = Math.atan2(y, x).toDeg()

The naming of the variables (lat1, lat2, dLon) has me confused.

If my initial lat lon is:

Latitude = -33.8830555556 Longitude = 151.216666667

and my destination lat and lon is:

Latitude = 22.25 Longitude = 114.1667

What variables need to match up to which lat and lons?

Is the dLon variable refering to the distance between the two points longitudinally?

Thanks a bunch!

Solution

Based on the JavaScript code, lat1 is the latitude of the initial point and lat2 is the latitude of the destination point.

Note that all latitudes and longitudes must be in radians; use math.rad() for the conversion.

Also the math library in Lua is called math, not Math.