Function TwoDimInterpol(x As Double, Y As Double, Matrix As Range, OrderX As Integer, OrderY As Integer) As Variant
'function to perform two-dimentional linear interpolation in elevation tables
'INPUT:
'-x Latitude
'-Y LONGITUDE
'-OrderX use digit 0 if X values are organized in descending manner, 1 if X values are ascending
'-OrderY use digit 0 if Y values are organized in descending manner, 1 if Y values are ascending
'Matrix: table organized in the following manner:

'         Y1     Y2     Y3     Y4     Y5
' X1    value  value  value  value  value
' X2    value  value  value  value  value
' X3    value  value  value  value  value
' X4    value  value  value  value  value

'Reading the dimensions of the matrix
'Number of rows
m = Matrix.Rows.Count
'Number of columns
N = Matrix.Columns.Count

'Checking is value X is within the Matrix ranges
If OrderX = 1 Then
    If x < Matrix(2, 1) Or x > Matrix(m, 1) Then
        Err = 1
    End If
Else
    If x > Matrix(2, 1) Or x < Matrix(m, 1) Then
        Err = 1
    End If
End If
'Checking is value Y is within the Matrix ranges
If OrderY = 1 Then
    If Y < Matrix(1, 2) Or Y > Matrix(1, N) Then
        Err = 1
    End If
Else
    If Y > Matrix(1, 2) Or Y < Matrix(1, N) Then
        Err = 1
    End If
End If
'If values are not in the matrix range return a message
flg = False
If Err = 1 Then
    TwoDimInterpol = "Value not in range"
Else
    'Searching through the table
    For i = 2 To m - 1
        If OrderX = 0 Then
            If x <= Matrix(i, 1) And x >= Matrix(i + 1, 1) Then
                For j = 2 To N - 1
                    If OrderY = 0 Then
                        If Y <= Matrix(1, j) And Y >= Matrix(1, j + 1) Then
                            flg = True
                            Exit For
                        End If
                    Else
                        If Y >= Matrix(1, j) And Y <= Matrix(1, j + 1) Then
                            flg = True
                            Exit For
                        End If
                    End If
                Next
            End If
        Else
            If x >= Matrix(i, 1) And x <= Matrix(i + 1, 1) Then
                For j = 2 To N - 1
                    If OrderY = 0 Then
                        If Y <= Matrix(1, j) And Y >= Matrix(1, j + 1) Then
                            flg = True
                            Exit For
                        End If
                    Else
                        If Y >= Matrix(1, j) And Y <= Matrix(1, j + 1) Then
                            flg = True
                            Exit For
                        End If
                    End If
                Next
            End If
        End If
        If flg = True Then
            Exit For
        End If
    Next
    VAR_x11_i = lininterpol(Matrix(i, 1), Matrix(i, j), Matrix(i + 1, 1), Matrix(i + 1, j), x)
    Var_x12_i = lininterpol(Matrix(i, 1), Matrix(i, j + 1), Matrix(i + 1, 1), Matrix(i + 1, j + 1), x)
    TwoDimInterpol = lininterpol(Matrix(1, j), VAR_x11_i, Matrix(1, j + 1), Var_x12_i, Y)
End If

End Function

Function lininterpol(x1, y1, x2, y2, x)
    lininterpol = (((y2 - y1) / (x2 - x1)) * (x - x1)) + y1
End Function