Hello,

I am trying to convert a JavaScript function into an Excel VBA. The
JavaScript function is as follows:

p1 and p2 contain the latitude and longitude in radians

LatLong.distVincenty = function(p1, p2) {
var a = 6378137, b = 6356752.3142, f = 1/298.257223563; // WGS-84
ellipsiod
var L = p2.lon - p1.lon;
var U1 = Math.atan((1-f) * Math.tan(p1.lat));
var U2 = Math.atan((1-f) * Math.tan(p2.lat));
var sinU1 = Math.sin(U1), cosU1 = Math.cos(U1);
var sinU2 = Math.sin(U2), cosU2 = Math.cos(U2);

var lambda = L, lambdaP = 2*Math.PI;
var iterLimit = 20;
while (Math.abs(lambda-lambdaP) 1e-12 && --iterLimit0) {
var sinLambda = Math.sin(lambda), cosLambda = Math.cos(lambda);
var sinSigma = Math.sqrt((cosU2*sinLambda) * (cosU2*sinLambda) +
(cosU1*sinU2-sinU1*cosU2*cosLambda) *
(cosU1*sinU2-sinU1*cosU2*cosLambda));
if (sinSigma==0) return 0; // co-incident points
var cosSigma = sinU1*sinU2 + cosU1*cosU2*cosLambda;
var sigma = Math.atan2(sinSigma, cosSigma);
var sinAlpha = cosU1 * cosU2 * sinLambda / sinSigma;
var cosSqAlpha = 1 - sinAlpha*sinAlpha;
if (cosSqAlpha==0) return Math.abs(a*L).toFixed(3); // two points
on equator
var cos2SigmaM = cosSigma - 2*sinU1*sinU2/cosSqAlpha;
var C = f/16*cosSqAlpha*(4+f*(4-3*cosSqAlpha));
lambdaP = lambda;
lambda = L + (1-C) * f * sinAlpha *
(sigma +
C*sinSigma*(cos2SigmaM+C*cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)));
}
if (iterLimit==0) return NaN // formula failed to converge

var uSq = cosSqAlpha * (a*a - b*b) / (b*b);
var A = 1 + uSq/16384*(4096+uSq*(-768+uSq*(320-175*uSq)));
var B = uSq/1024 * (256+uSq*(-128+uSq*(74-47*uSq)));
var deltaSigma =
B*sinSigma*(cos2SigmaM+B/4*(cosSigma*(-1+2*cos2SigmaM*cos2SigmaM)-

B/6*cos2SigmaM*(-3+4*sinSigma*sinSigma)*(-3+4*cos2SigmaM*cos2SigmaM)));
var s = b*A*(sigma-deltaSigma);

s = s.toFixed(3); // round to 1mm precision
return s;
}


To the best of my knowledge, I have the following VBA code:

Public Const Pi = 3.14159265358979

Public Function Radians(x)
Radians = Pi * x / 180#
End Function

Function SDistance(lat1, lat2, ht1, long1, long2, ht2) ' in meters

' Calculate geodesic distance (in m) between two points specified by
latitude/longitude
' using Vincenty inverse formula for ellipsoids. The latitude/longitude
are in
' decimal degrees.

a = 6378137 ' Part of the WGS-84
b = 6356752.3142 ' ellipsiod datum
f = 1 / 298.257223563

lat1 = Radians(lat1) 'Convert decimal degrees
lat2 = Radians(lat2) 'to radians since Excel trig
long1 = Radians(long1) 'functions use radians by
long2 = Radians(long2) 'default

L = long2 - long1
U1 = Atn((1 - f) * Tan(lat1))
U2 = Atn((1 - f) * Tan(lat2))
sinU1 = Sin(U1)
cosU1 = Cos(U1)
sinU2 = Sin(U2)
cosU2 = Cos(U2)

lambda = L
lambdaP = 2 * Pi
iterLimit = 20

Do While ((Abs(lambda - lambdaP) 1 / (10 ^ 12)) And (iterLimit
0))

iterLimit = iterLimit - 1

sinLambda = Sin(lambda)
cosLambda = Cos(lambda)
sinSigma = ((cosU2 * sinLambda) * (cosU2 * sinLambda) + _
(cosU1 * sinU2 - sinU1 * cosU2 * cosLambda) * (cosU1 * sinU2 -
sinU1 * cosU2 * cosLambda)) ^ (1 / 2)

cosSigma = sinU1 * sinU2 + cosU1 * cosU2 * cosLambda
sigma = Application.WorksheetFunction.Atan2(sinSigma, cosSigma)
sinAlpha = cosU1 * cosU2 * sinLambda / sinSigma
cosSqAlpha = 1 - sinAlpha * sinAlpha

cos2SigmaM = cosSigma - 2 * sinU1 * sinU2 / cosSqAlpha
c = f / 16 * cosSqAlpha * (4 + f * (4 - 3 * cosSqAlpha))
lambdaP = lambda
lambda = L + (1 - c) * f * sinAlpha * (sigma + c * sinSigma *
(cos2SigmaM + c * cosSigma * (-1 + 2 * cos2SigmaM * cos2SigmaM)))

Loop


uSq = cosSqAlpha * (a * a - b * b) / (b * b)
a = 1 + uSq / 16384 * (4096 + uSq * (-768 + uSq * (320 - 175 * uSq)))
b = uSq / 1024 * (256 + uSq * (-128 + uSq * (74 - 47 * uSq)))
deltaSigma = b * sinSigma * (cos2SigmaM + b / 4 * (cosSigma * (-1 + 2
* cos2SigmaM * cos2SigmaM) - b / 6 * cos2SigmaM * (-3 + 4 * sinSigma *
sinSigma) * (-3 + 4 * cos2SigmaM * cos2SigmaM)))
s = b * a * (sigma - deltaSigma)

s = Round(s, 3) 'round to 1mm precision

If (cosSqAlpha = 0) Then
s = Abs(a * L) 'two points on equator
s = Round(s, 3)
End If

htall = ht1 - ht2
sqval = htall ^ 2 + s ^ 2

SDistance = s


If (sinSigma = 0) Then SDistance = 0 'co-incident points

If (iterLimit = 0) Then SDistance = "Error" 'formula failed to
converge

End Function


Unfortunately, I am not getting the same result with the JavaScript
function. Can anyone help?

Thanks!