Attribute VB_Name = "modTerrain"
'The number of points in each cell
Dim points(0 To gridSize - 1, 0 To gridSize - 1) As Integer
Dim grid(0 To gridSize - 1, 0 To gridSize - 1) As Double


Public Sub setpoint(east As Double, north As Double, masl As Double, minEast As Double, maxEast As Double, _
                    minNorth As Double, maxNorth As Double)
   Dim e As Integer
   Dim n As Integer
   Dim tempE As Double
   Dim tempN As Double
   Dim range As Double
   
   'Easting first
   range = maxEast - minEast
   range = 1.000001 * range
   tempE = (east - minEast) / range
   tempE = gridSize * tempE
   e = Int(tempE)
      
   'now northing
   range = maxNorth - minNorth
   range = 1.000001 * range
   tempN = (north - minNorth) / range
   tempN = gridSize * tempN
   n = Int(tempN)
   
   If grid(e, n) > 0 Then
      grid(e, n) = ((grid(e, n) * points(e, n)) + masl) / (points(e, n) + 1)
      
   Else
      grid(e, n) = masl
   End If
   points(e, n) = points(e, n) + 1
   
End Sub

Private Sub countpoints()
    Dim e As Integer
    Dim n As Integer
    Dim count As Long
    
    count = 0
    For e = 0 To gridSize - 1
    For n = 0 To gridSize - 1
    count = count + points(e, n)
    Next n
    Next e
    
    count = 0
    For e = 0 To gridSize - 1
    For n = 0 To gridSize - 1
    If grid(e, n) > 0 Then
        count = count + 1
    End If
 
    Next n
    Next e
 
End Sub
Public Sub makeGrid()
  Dim i As Integer
  Dim minN As Double
  Dim minE As Double
  Dim maxN As Double
  Dim maxE As Double
  
  Let minN = 1000000
  Let minE = 1000000
  Let maxN = 0
  Let maxE = 0
    
  Let minN = getMin(Northing)
  Let minE = getMin(Easting)
  Let maxN = getMax(Northing)
  Let maxE = getMax(Easting)
  
  frmProgress.ProgressBar1.Min = 0
  frmProgress.ProgressBar1.Max = RecordCounter
  frmProgress.ProgressBar1.Value = frmProgress.ProgressBar1.Min
  frmProgress.ProgressBar1.Visible = True
  frmProgress.txtName.Text = "Generating Grid"
  frmProgress.Show
  
  For i = 1 To RecordCounter
    Call setpoint(Easting(i), Northing(i), masl(i), minE, maxE, minN, maxN)
    frmProgress.ProgressBar1.Value = frmProgress.ProgressBar1.Value + 1
    frmProgress.Refresh
  Next i
  frmProgress.Hide
  
End Sub

Public Function getMin(arr() As Double) As Double
    Dim result As Double
    Dim i As Integer
    
    result = arr(1)
    
    For i = 2 To RecordCounter
        If arr(i) < result Then
            result = arr(i)
        End If
    Next i
    
    getMin = result
End Function
Public Function countNorth(n As Integer) As Integer
   'Counts the number of points east for a given northing
   Dim count As Integer
   Dim i As Integer
   
   Let count = 0
   For i = 0 To (gridSize - 1) 'Move through the grid
     If grid(i, n) > 0 Then 'test if a value occurs at each grid point
       Let count = count + 1
     End If
   Next i
   countNorth = count
End Function
Public Function countEast(e As Integer) As Integer
   'Counts the number of points east for a given northing
   Dim count As Integer
   Dim i As Integer
   
   Let count = 0
   For i = 0 To (gridSize - 1) 'Move through the grid
     If grid(e, i) > 0 Then 'test if a value occurs at each grid point
       Let count = count + 1
     End If
   Next i
   countEast = count
End Function

Public Function NextE(n As Integer, Start As Integer) As Integer
   'Finds the Next Point along one grid line heading east in the grid
   Dim i As Integer
   Dim result As Integer
   
   Let result = -1
   'Do While i < gridSize And grid(i, N) = 0   'Test if a value found and if the edge of the grid is reached
   '  i = i + 1
   'Loop
   For i = Start To gridSize - 1
     If grid(i, n) > 0 Then
        result = i
        Exit For
     End If
   Next i
   
   NextE = result
End Function

Public Function NextN(e As Integer, Start As Integer) As Integer
   'Finds the Next Point along one grid line heading north in the grid
   Dim i As Integer
   Dim result As Integer
   
   Let result = -1
   'Do While grid(E, i) = 0 And i < gridSize 'Test if a value found and if the edge of the grid is reached
    ' i = i + 1
   'Loop
   For i = Start To gridSize - 1
     If grid(e, i) > 0 Then
        result = i
        Exit For
     End If
   Next i
   
   NextN = result
End Function

Public Sub inTerPolate()
  'Estimate the values of cells in the grid between the measured points
  'Firstly in an easterly direction then northerly
  'Negate the interpolated points so they can be determine from the measured ones
  Dim e As Integer
  Dim n As Integer
  Dim i As Integer
  Dim iFrom As Integer
  Dim iTo As Integer
  Dim STeps As Integer
  Dim Interval As Integer
  Dim HeightDiff As Double
  Dim temp As Double
  
  frmProgress.ProgressBar1.Min = 0
  frmProgress.ProgressBar1.Max = gridSize + gridSize
  frmProgress.ProgressBar1.Value = frmProgress.ProgressBar1.Min
  frmProgress.ProgressBar1.Visible = True
  frmProgress.Show
    
  'East first
  For e = 0 To gridSize - 1
     count = countEast(e)
     If count > 1 Then
        Let STeps = 0
        Let iFrom = 0
        Do
           Let iFrom = NextN(e, iFrom)
           Let iTo = NextN(e, iFrom + 1)
           STeps = STeps + 1
           Interval = iTo - iFrom
           HeightDiff = grid(e, iTo) - grid(e, iFrom)
           For i = iFrom + 1 To iTo - 1
             grid(e, i) = (i - iFrom) * HeightDiff / Interval + grid(e, iFrom)
             Let grid(e, i) = -grid(e, i)
           Next i
           iFrom = iTo
        Loop While STeps < count - 1
     End If
     frmProgress.ProgressBar1.Value = frmProgress.ProgressBar1.Value + 1
     frmProgress.Refresh
  Next e
  'next north
  For n = 0 To gridSize - 1
     count = countNorth(n)
     If count > 1 Then
        Let STeps = 0
        Let iFrom = 0
        Do
           Let iFrom = NextE(n, iFrom)
           Let iTo = NextE(n, iFrom + 1)
           STeps = STeps + 1
           Interval = iTo - iFrom
           HeightDiff = grid(iTo, n) - grid(iFrom, n)
           For i = iFrom + 1 To iTo - 1
             Let temp = grid(i, n)
             grid(i, n) = (i - iFrom) * HeightDiff / Interval + grid(iFrom, n)
             Let grid(i, n) = -grid(i, n)
             If Abs(temp) > 0 Then
                'Due to the fact points heights are geing averaged there might be a
                'difference in height between the north and east grid lines
                'so we are averaging out the height at the intersections
                Let grid(i, n) = (Abs(temp) + Abs(grid(i, n))) / 2
                Let grid(i, n) = -grid(i, n)
             End If
           Next i
           iFrom = iTo
        Loop While STeps < count - 1
     End If
     frmProgress.ProgressBar1.Value = frmProgress.ProgressBar1.Value + 1
     frmProgress.Refresh
  Next n
  frmProgress.Hide
End Sub
Public Sub resetPoints()
   'resets the negative values (used to differenciate calulated values)
   Dim count As Long
   
   Dim e As Integer
   Dim n As Integer
   
   For e = 0 To gridSize - 1
      For n = 0 To gridSize - 1
         grid(e, n) = Abs(grid(e, n))
         If (grid(e, n) > 0) Then
             count = count + 1
        End If
      Next n
   Next e

End Sub
Public Function getMax(arr() As Double) As Double
    Dim result As Double
    Dim i As Integer
    
    result = arr(1)
    
    For i = 2 To RecordCounter
        If arr(i) > result Then
            result = arr(i)
        End If
    Next i
    
    getMax = result
End Function

Private Sub MapTerrain(minMASL As Double, maxMASL As Double)
  'MapTerrain scale the measured data so that they correspond
  'to the height range of MASL.

  Dim e As Integer
  Dim n As Integer
  Dim rangeMASL As Double
  
  Let rangeMASL = maxMASL - minMASL
    For e = 0 To gridSize - 1
      For n = 0 To gridSize - 1
    
       If grid(e, n) > 0 Then
          Terrain(e, n) = _
            Int(255 * (grid(e, n) - minMASL) / rangeMASL)
          If (Terrain(e, n) > 255) Then
            MsgBox "Terrain too big", vbOKOnly
          End If
          If (Terrain(e, n) < 0) Then
            MsgBox "Terrain too small", vbOKOnly
          End If
        Else
            Terrain(e, n) = 0
        End If
       Next n
    Next e

End Sub


Public Sub genTerrain()
  Dim minMASL As Double
  Dim maxMASL As Double
  
  minMASL = getMin(masl)
  maxMASL = getMax(masl)
  
  frmProgress.txtName.Text = "Interpolating Points Pass 1 of 2"
  Call inTerPolate
  Call resetPoints
  'functions are recalled to cover any new points exposed
  frmProgress.txtName.Text = "Interpolating Points Pass 2 of 2"
  Call inTerPolate
  Call resetPoints
  Call MapTerrain(minMASL, maxMASL)
End Sub