Thread: Translate from javascript to VBA

This one is beyond me.

I'm trying to work out the compass bearing of a direct (rhumb line, constant bearing) route between two points on a sphere using latitude and longitude in radians. I've found a formula online but don't understand a word of it:

Formula:	Δφ = ln(tan(lat2/2+π/4)/tan(lat1/2+π/4))	 [= the ‘stretched’ latitude difference]
if E:W line,	q = cos(lat1)	 
otherwise,	q = Δlat/Δφ	 
 	d = √(Δlat² + q².Δlon²).R	[pythagoras]
 	θ = atan2(Δlon, Δφ)	 
 	where ln is natural log, Δlon is taking shortest route (<180º), and R is the earth’s radius

Someone much clevered than me has posted this in javascript:

var dPhi = Math.log(Math.tan(lat2/2+Math.PI/4)/Math.tan(lat1/2+Math.PI/4));
var q = (!isNaN(dLat/dPhi)) ? dLat/dPhi : Math.cos(lat1);  // E-W line gives dPhi=0

// if dLon over 180° take shorter rhumb across 180° meridian:
if (Math.abs(dLon) > Math.PI) {
  dLon = dLon>0 ? -(2*Math.PI-dLon) : (2*Math.PI+dLon);
}
var d = Math.sqrt(dLat*dLat + q*q*dLon*dLon) * R;
var brng = Math.atan2(dLon, dPhi);

And I dont speak java. I vaguely get the first line but don't understand the var q = line at all. Does anyone speak Java in here?

And yes, I realise I've put a formula in [ code ] tags but it may as well be in code.....a 64bit encrypted code.

I'm not going to even try to understand the maths, but the js above can be written as the below, hope it makes more sense to you than me!

Dim pi As Double

Sub JStoVBA()
Dim dPhi As Double
Dim brng As Double
Dim dLon As Double
Dim dLat As Double
Dim q As Double
Dim R As Double
Dim d As Double
Dim lat2
Dim lat1


pi = 4 * Atn(1)

'Formula
dPhi = Log(Tan(lat2 / 2 + pi / 4) / Tan(lat1 / 2 + pi / 4))

'IF E:W Line
On Error Resume Next
If dLat / dPhi Then
    q = Cos(lat1)
Else
'OtherWise
    q=dLat/dPhi
End If
Err.Clear

If Abs(dLon) > pi Then
    If dLon > 0 Then
        dLon = -(2 * pi - dLon)
    Else
        dLon = (2 * pi + dLon)
    End If
End If

d = Sqr(dLat * dLat + q * q * dLon * dLon) * R

brng = Atan2(dLon, dPhi)

        

End Sub

Function Atan2(y As Double, x As Double) As Double

If x > 0 Then
    Atan2 = Atn(y / x)
  ElseIf x < 0 Then
    Atan2 = Sgn(y) * (pi - Atn(Abs(y / x)))
  ElseIf y = 0 Then
    Atan2 = 0
  Else
    Atan2 = Sgn(y) * pi / 2
  End If
End Function