This is a simple snippet of code...
B4X:
' Antipodes -Wikipedia: "The Antipode of any spot on Earth is the point on Earth's surface diametrically opposite to it."
' In other words: Given a spot on Earth, the Antipode is the spot on the exact opposite side of the world through the center.
' Given the decimal degrees for Latitude and Longitude of a spot, these two subs will return the Antipode of that spot
' Use like: Log(AntipodeLat(-27.683528)) -and- Log(AntipodeLng(130.078125))
Sub AntipodeLat (Lat As Double) As Double
Return Lat * -1
End Sub
Sub AntipodeLng (Lng As Double) As Double
If Lng <= 0 Then
Return Lng + 180
Else
Return Lng - 180
End If
End Sub