Nice Label Algorithm for Charts with minimum ticks

Question

I need to calculate the Ticklabels and the Tickrange for charts manually.

I know the \"standard\" algorithm for nice ticks (see http://books.google.de/books?id=fvA7

Answer 1

This is the VB.NET version.

Public Class NiceScale

Private minPoint As Double
Private maxPoint As Double
Private maxTicks As Double = 10
Private tickSpacing
Private range As Double
Private niceMin As Double
Private niceMax As Double

Public Sub New(min As Double, max As Double)
    minPoint = min
    maxPoint = max
    calculate()
End Sub

Private Sub calculate()
    range = niceNum(maxPoint - minPoint, False)
    tickSpacing = niceNum(range / (maxTicks - 1), True)
    niceMin = Math.Floor(minPoint / tickSpacing) * tickSpacing
    niceMax = Math.Ceiling(maxPoint / tickSpacing) * tickSpacing
End Sub

Private Function niceNum(range As Double, round As Boolean) As Double
    Dim exponent As Double '/** exponent of range */
    Dim fraction As Double '/** fractional part of range */
    Dim niceFraction As Double '/** nice, rounded fraction */

    exponent = Math.Floor(Math.Log10(range))
    fraction = range / Math.Pow(10, exponent)

    If round Then
        If (fraction < 1.5) Then
            niceFraction = 1
        ElseIf (fraction < 3) Then
            niceFraction = 2
        ElseIf (fraction < 7) Then
            niceFraction = 5
        Else
            niceFraction = 10
        End If
    Else
        If (fraction <= 1) Then
            niceFraction = 1
        ElseIf (fraction <= 2) Then
            niceFraction = 2
        ElseIf (fraction <= 5) Then
            niceFraction = 5
        Else
            niceFraction = 10
        End If
    End If

    Return niceFraction * Math.Pow(10, exponent)
End Function

Public Sub setMinMaxPoints(minPoint As Double, maxPoint As Double)
    minPoint = minPoint
    maxPoint = maxPoint
    calculate()
End Sub

Public Sub setMaxTicks(maxTicks As Double)
    maxTicks = maxTicks
    calculate()
End Sub

Public Function getTickSpacing() As Double
    Return tickSpacing
End Function

Public Function getNiceMin() As Double
    Return niceMin
End Function

Public Function getNiceMax() As Double
    Return niceMax
End Function

End Class