Private Function IsValidLatitudeLongitude(lat As Double, lon As Double) As Boolean
 If lat < -90 OrElse lat > 90 OrElse lon <= -180 OrElse lon > 180 Then
  Return False
 End If
 Return True
End Function
  

Whilst some parts of Northern Ireland could be represented by the OS National Grid for Great Britain, they are normally represented using the Irish National Grid.

Public Shared Function IsValidGpsForOsGrid(lat As Double, lon As Double) As Boolean
 ' test valid for all land areas within England, Wales and Scotland (including islands)
 ' offshore locations close to the extreme limits of the OS National Grid could return false "Invalid" result
 If lon < -8 Or lon > 1.9 Then Return False
 If lat < 49.87 Or lat > 61 Then Return False
 If lat < -7 And lon < 54 Then Return False
 Return True
End Function
  

Private Function Degrees_To_DegreesMinutes(deg As Double) As DegreesMinutes
 Dim ret As DegreesMinutes
 ret.Degrees = Math.Floor(deg)
 ret.Minutes = 60 * (deg - ret.Degrees)
 Return ret
End Function
'
Public Structure DegreesMinutes
 Dim Degrees As Integer
 Dim Minutes As Double
End Structure
  

Private Function Degrees_To_DegreesMinutesSeconds(deg As Double) As DegreesMinutesSeconds
 Dim ret As DegreesMinutesSeconds
 Dim minutes As Double
 ret.Degrees = Math.Floor(deg)
 minutes = 60 * (deg - ret.Degrees)
 ret.Minutes = Math.Floor(minutes)
 ret.Seconds = 60 * (minutes - ret.Minutes)
 Return ret
End Function
'
Public Structure DegreesMinutesSeconds
 Dim Degrees As Integer
 Dim Minutes As Integer
 Dim Seconds As Double
End Structure
  

Private Function DegreesMinutesToDegrees(degrees As Double, minutes As Double) As Double
 Return degrees + (minutes / 60)
End Function
  

Private Function DegreesMinutesSecondsToDegrees(degrees As Double, minutes As Double, seconds As Double) As Double
 Return degrees + (minutes / 60) + (seconds / 3600)
End Function
  

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