In this tutorial, we will show you how to calculate the distance between two locations geolocated by using latitude and longitude in .NET. This distance calculation uses the **Spherical Law of Cosines**, which uses trigonometry to measure the curvature of the earth, to accurately measure the distances on the Earth.

```
<%
const pi = 3.14159265358979323846
Function distance(lat1, lon1, lat2, lon2, unit)
Dim theta, dist
If lat1 = lat2 And lon1 = lon2 Then
distance = 0
Else
theta = lon1 - lon2
dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) + cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta))
dist = acos(dist)
dist = rad2deg(dist)
distance = dist * 60 * 1.1515
Select Case ucase(unit)
Case "K"
distance = distance * 1.609344
Case "N"
distance = distance * 0.8684
End Select
End If
End Function
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'::: This function get the arccos function from arctan function :::
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Function acos(rad)
If Abs(rad) <> 1 Then
acos = pi/2 - Atn(rad / Sqr(1 - rad * rad))
ElseIf rad = -1 Then
acos = pi
End If
End function
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'::: This function converts decimal degrees to radians :::
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Function deg2rad(Deg)
deg2rad = cdbl(Deg * pi / 180)
End Function
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'::: This function converts radians to decimal degrees :::
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Function rad2deg(Rad)
rad2deg = cdbl(Rad * 180 / pi)
End Function
response.write distance(32.9697, -96.80322, 29.46786, -98.53506, "M") & " Miles<br>"
response.write distance(32.9697, -96.80322, 29.46786, -98.53506, "K") & " Kilometers<br>"
response.write distance(32.9697, -96.80322, 29.46786, -98.53506, "N") & " Nautical Miles<br>"
%>
```

The code above creates the function named **distance **to calculate the distance between two locations. It implies the simple spherical law of cosines that gives well-conditioned results down to distances as small as a few meters on the Earth’s surface. The distance function makes use of the spherical law of cosines formula `cos `

and derived into the distance calculation.*c* = cos *a* cos *b* + sin *a* sin *b* cos *C*

Parameters that are passed to the distance function are:**lat1**, **lon1** = Latitude and Longitude of point 1 in decimal degrees**lat2**, **lon2 **= Latitude and Longitude of point 2 in decimal degrees**unit **= the unit you desire for results where ‘M’ is the statute miles (default), ‘K’ is kilometers and ‘N’ is nautical miles