ChartDirector 6.0 (ASP/COM/VB Edition)

General Curve Fitting




This example demonstrates the LOWESS general purpose curve fitting that is built into ChartDirector.

In regression curve fitting, a function type have to be chosen first, and the data are used to compute the best parameters of that function. For example, in polynomial regression, the function type is a polynomial of a given degree, and the data are used to determine the optimal polynomial coefficients.

However, in many applications, the function type is not known or not expressible in algebraic form. To handle these cases, ChartDirector supports a general curve fitting algorithm known as LOWESS. For details, please refer to ArrayMath.lowess and ArrayMath.lowess2.

The LOWESS algorithm only adjusts the points to smoothen them. They still need to be joined together. In this example, the adjusted points are joined with a spline layer using XYChart.addSplineLayer.

Source Code Listing

[Web Version (in ASP)] aspdemo\curvefitting.asp
<%@ language="vbscript" %>
<%
Set cd = CreateObject("ChartDirector.API")

' Use random table to generate a random series. The random table is set to 1 col x 51 rows, with 9
' as the seed
Set rantable = cd.RanTable(9, 1, 51)

' Set the 1st column to start from 100, with changes between rows from -5 to +5
Call rantable.setCol(0, 100, -5, 5)

' Get the 1st column of the random table as the data set
data = rantable.getCol(0)

' Create a XYChart object of size 600 x 300 pixels
Set c = cd.XYChart(600, 300)

' Set the plotarea at (50, 35) and of size 500 x 240 pixels. Enable both the horizontal and vertical
' grids by setting their colors to grey (0xc0c0c0)
Call c.setPlotArea(50, 35, 500, 240).setGridColor(&Hc0c0c0, &Hc0c0c0)

' Add a title to the chart using 18 point Times Bold Itatic font.
Call c.addTitle("LOWESS Generic Curve Fitting Algorithm", "timesbi.ttf", 18)

' Set the y axis line width to 3 pixels
Call c.yAxis().setWidth(3)

' Add a title to the x axis using 12pt Arial Bold Italic font
Call c.xAxis().setTitle("Server Load (TPS)", "arialbi.ttf", 12)

' Set the x axis line width to 3 pixels
Call c.xAxis().setWidth(3)

' Set the x axis scale from 0 - 50, with major tick every 5 units and minor tick every 1 unit
Call c.xAxis().setLinearScale(0, 50, 5, 1)

' Add a blue layer to the chart
Set layer = c.addLineLayer2()

' Add a red (0x80ff0000) data set to the chart with square symbols
Call layer.addDataSet(data, &H80ff0000).setDataSymbol(cd.SquareSymbol)

' Set the line width to 2 pixels
Call layer.setLineWidth(2)

' Use lowess for curve fitting, and plot the fitted data using a spline layer with line width set to
' 3 pixels
Call c.addSplineLayer(cd.ArrayMath(data).lowess().result(), &H0000ff).setLineWidth(3)

' Set zero affinity to 0 to make sure the line is displayed in the most detail scale
Call c.yAxis().setAutoScale(0, 0, 0)

' Output the chart
Response.ContentType = "image/png"
Response.BinaryWrite c.makeChart2(cd.PNG)
Response.End
%>

[Windows Version (in Visual Basic)] vbdemo\curvefitting.cls
Public Sub createChart(viewer As Object, chartIndex As Integer)

    Dim cd As New ChartDirector.API

    ' Use random table to generate a random series. The random table is set to 1 col x 51 rows, with
    ' 9 as the seed
    Dim rantable As RanTable
    Set rantable = cd.RanTable(9, 1, 51)

    ' Set the 1st column to start from 100, with changes between rows from -5 to +5
    Call rantable.setCol(0, 100, -5, 5)

    ' Get the 1st column of the random table as the data set
    Dim data()
    data = rantable.getCol(0)

    ' Create a XYChart object of size 600 x 300 pixels
    Dim c As XYChart
    Set c = cd.XYChart(600, 300)

    ' Set the plotarea at (50, 35) and of size 500 x 240 pixels. Enable both the horizontal and
    ' vertical grids by setting their colors to grey (0xc0c0c0)
    Call c.setPlotArea(50, 35, 500, 240).setGridColor(&Hc0c0c0, &Hc0c0c0)

    ' Add a title to the chart using 18 point Times Bold Itatic font.
    Call c.addTitle("LOWESS Generic Curve Fitting Algorithm", "timesbi.ttf", 18)

    ' Set the y axis line width to 3 pixels
    Call c.yAxis().setWidth(3)

    ' Add a title to the x axis using 12pt Arial Bold Italic font
    Call c.xAxis().setTitle("Server Load (TPS)", "arialbi.ttf", 12)

    ' Set the x axis line width to 3 pixels
    Call c.xAxis().setWidth(3)

    ' Set the x axis scale from 0 - 50, with major tick every 5 units and minor tick every 1 unit
    Call c.xAxis().setLinearScale(0, 50, 5, 1)

    ' Add a blue layer to the chart
    Dim layer As LineLayer
    Set layer = c.addLineLayer2()

    ' Add a red (0x80ff0000) data set to the chart with square symbols
    Call layer.addDataSet(data, &H80ff0000).setDataSymbol(cd.SquareSymbol)

    ' Set the line width to 2 pixels
    Call layer.setLineWidth(2)

    ' Use lowess for curve fitting, and plot the fitted data using a spline layer with line width
    ' set to 3 pixels
    Call c.addSplineLayer(cd.ArrayMath(data).lowess().result(), &H0000ff).setLineWidth(3)

    ' Set zero affinity to 0 to make sure the line is displayed in the most detail scale
    Call c.yAxis().setAutoScale(0, 0, 0)

    ' Output the chart
    Set viewer.Picture = c.makePicture()

    'include tool tip for the chart
    viewer.ImageMap = c.getHTMLImageMap("clickable", "", "title='({x}, {value|2})'")

End Sub