10/18/06
jChart - Two Y-Axis Chart Example
About jChart
The line chart uses the LineOverlay and BarOverlay overlay types to
show how can two series on a single chart can be displayed using different
Y-Axes.
ASP.NET 2.0 example
HTML
This is the HTML that displays the chart on the page. The image map is optional
and is used to implement drill-down.
<div>
<img src="<%=me.ImageURL %>" alt="" usemap="#MyMap" />
<map id="Map1" name="MyMap">
<%=Me.ImageMap%>
</map>
</div>
Code-Behind
The following code uses two environment variables.
Application("TempPath") is an application variable that contains the path to the
directory in which temporary images should be stored in the format "c:\mywebsite\temp\"
Session("TempURL") is a session variable that contains the base URL of the
directory in which temporary images are be stored in the format "http://myhost/temp/"
The chart object should be global as it is initialized in the Page_Load function
and then referenced by the ImageURL and ImageMap functions later on.
Dim moChart As jChart.GraphChart
The Page_Load event is where the heavy lifting gets done. It is here that the
appearance of the chart (background color, size, chart type, etc.) is set, the X and Y axis
values are set, and series are created and added to the chart.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
'---Let's set up the chart.
' We'll make it 600 pixels wide by 400 pixels high.
moChart = New jChart.GraphChart(600, 400)
moChart.ChartName = "Two Y-Axis Demo"
moChart.Font = New Font(System.Drawing.FontFamily.GenericSansSerif, 11, FontStyle.Bold)
'---We'll specify a 10 pixel border all the way around the inside
' edge of the chart.
moChart.ChartDimensions.FrameSize = 10
'---The Y Axis column on the left will be 20 pixels wide.
moChart.ChartDimensions.YAxis1LabelColumnWidth = 20
'---The Y Axis column on the right will also be 20 pixels wide.
moChart.ChartDimensions.YAxis2LabelColumnWidth = 20
'---The X Axis row on the bottom will be 20 pixels high.
moChart.ChartDimensions.XAxisLabelRowHeight = 20
'---Let's add the X Axis values
' We'll have 7 values and in place of the numeric values we'll
' display friendly labels.
Dim oXAxisValues() As Single = {0, 1, 2, 3, 4, 5, 6}
Dim oXAxisLabels() As String = {"SU", "MO", "TU", "WE", "TH", "FR", "SA"}
'---We'll create an XAxis object using the ChartDimensions object
' from the chart we just created.
Dim oXAxis As New jChart.XAxis(moChart.ChartDimensions, oXAxisValues)
'---Let's tell the X Axis about the friendly labels to display in place
' of numbers.
oXAxis.XAxisLabels = oXAxisLabels
oXAxis.AxisName = "Days"
'---OK, finally let's tell the chart about its X Axis.
moChart.XAxis = oXAxis
'---Now, let's set up the Y Axis for the left side.
' We'll define 8 values. We could specify labels for our Y Axis values just as
' we did for our X Axis values but we won't.
Dim oYAxis1Values() As Single = {20, 25, 30, 35, 40, 45, 50, 55}
'Dim oYAxis1Labels() As String = {"20", "25", "30", "35", "40", "45", "50", "55"}
'---We'll tell our new Y Axis object that it will be on the left side of the chart
' and we'll pass in a reference to the chart's ChartDimension object so the Y Axis
' will know how big it needs to be.
Dim oYAxis1 As New jChart.YAxis(jChart.YAxis.Alignment.Left, moChart.ChartDimensions, oYAxis1Values)
oYAxis1.AxisName = "Left-side Y Axis"
'---Now, let's set up the Y Axis for the right side.
' We'll use 8 values here as well.
Dim oYAxis2Values() As Single = {0, 5, 10, 15, 20, 25, 30, 35}
'---We'll tell our new Y Axis object that it will be on the right side of the chart
' and we'll pass in a reference to the chart's ChartDimension object so the Y Axis
' will know how big it needs to be.
Dim oYAxis2 As New jChart.YAxis(jChart.YAxis.Alignment.Right, moChart.ChartDimensions, oYAxis2Values)
oYAxis2.AxisName = "Right-side Y Axis"
'---Now let's tell the chart about our Y Axes
moChart.YAxis1 = oYAxis1
moChart.YAxis2 = oYAxis2
'---Finally, let's show some sample values.
' We'll make the values random, for more realism.
' Since we'll have two series, we'll need two sets of sample values. We'll
' call them "oValues1" and "oValues2"
' There will be 7 values in each series, just as there are 7 points on the X Axis.
' The series objects expect an array of single, so that's what we'll make.
Dim oValues1(8) As Single
Dim oValues2(8) As Single
Randomize(Environment.TickCount)
For iX As Short = 0 To 7
oValues1(iX) = Rnd() * 35 + 20
oValues2(iX) = Rnd() * 35
Next
'---The Bar series will be the first series drawn, so we'll use oValues1 as source data for it.
Dim oBarSeries As New jChart.Overlay.Series.BarSeries
With oBarSeries
'---We will call our series "series one".
' This value is accessible on drill-down from the image map.
.Name = "Series One"
'---Now we'll give the series the values it should use.
.Values = oValues1
'---The series will be orange in color
.Color = Color.Orange
'---The series will be slightly transparent (75% opaque)
.Opacity = 0.75
End With
'---The Line series will be the second series drawn, so we'll use oValues2 as source data for it.
Dim oLineSeries As New jChart.Overlay.Series.LineSeries
With oLineSeries
'---We will call our series "series two".
' This value is accessible on drill-down from the image map.
.Name = "Series Two"
'---Now we'll give the series the values it should use.
.Values = oValues2
'---The series will be green in color
.Color = Color.Green
'---The series will be slightly transparent (75% opaque)
.Opacity = 0.75
End With
'---Since we have two Y Axes, we'll need two overlay objects.
' Each overlay can refer to only a single Y Axis.
' The first overlay will use the left-hand Y Axis object.
'---We need to tell the overlay which dimensions and axes to use when
' we create it.
Dim oBarOverlay As New jChart.Overlay.BarOverlay(moChart.ChartDimensions, oXAxis, oYAxis1)
'---Let's add the series to the overlay
oBarOverlay.Series.Add(oBarSeries)
'---Let's add the overlay to the chart.
moChart.OverLays.Add(oBarOverlay)
'---Now we need a second overlay for our second series since it will refer to
' a right-hand Y Axis.
'---We need to tell the overlay which dimensions and axes to use when
' we create it.
Dim oLineOverlay As New jChart.Overlay.LineOverlay(moChart.ChartDimensions, oXAxis, oYAxis2)
'---Let's add the series to the overlay
oLineOverlay.Series.Add(oLineSeries)
'---Let's add the overlay to the chart.
moChart.OverLays.Add(oLineOverlay)
'---OK. All done. Now let's draw the chart.
' We'll start by creating a bitmap onto which the chart will be drawn.
' We do it this way so that the bitmap can be shared (a background image
' perhaps?)
Dim oPicture As New Bitmap( _
moChart.ChartDimensions.OuterWidth, _
moChart.ChartDimensions.OuterHeight, _
System.Drawing.Imaging.PixelFormat.Format24bppRgb)
'---Now that we've created the bitmap, we'll draw the chart on it and save it
' to a temporary location on the server in JPEG format. The charting object
' creates a unique filename for our new chart. This unique filename is
' accessible via the chart's FileName property (see ImageURL)
'---The path where the image will be saved must have write access for the ASPNET
' process enabled.
moChart.SaveChartToFile( _
Application("TempPath"), _
System.Drawing.Imaging.ImageFormat.Jpeg)
End Sub
The ImageURL property provides the name of the chart image that was created during
Page_Load to the IMG tag on the page.
Protected ReadOnly Property ImageURL() As String
Get
If moChart Is Nothing Then
Return ""
Else
Return Session("TempURL") & moChart.FileName
End If
End Get
End Property
The ImageMap property constructs and provides the image map that allows
for drill-down capability.
Protected ReadOnly Property ImageMap() As String
Get
If moChart Is Nothing Then
Return ""
Else
Return MakeImageMapString()
End If
End Get
End Property
Here we build the image map from the collection of chart regions. This is
done in the code behind block so that it can be customized--perhaps only
certain series should have drill-down enabled, and of course you will want
to customize the action that occurs when a series value is clicked on.
Private Function MakeImageMapString() As String
Dim sImageMap As String = ""
For Each oRegion As jChart.RegionArea In moChart.RegionList
Dim sCoords As String = ""
Dim oPoints As Point() = oRegion.SeriesPoints
sCoords = oPoints(0).X & "," & oPoints(0).Y
For iPoint As Integer = 1 To oPoints.GetUpperBound(0)
sCoords = sCoords & "," & oPoints(iPoint).X & "," & oPoints(iPoint).Y
Next
Dim sArea As String = "<area " & _
" shape=" & Chr(34) & "poly" & Chr(34) & _
" coords=" & Chr(34) & sCoords & Chr(34) & _
" href=" & Chr(34) & "javascript:alert('You clicked on " & oRegion.SeriesName & " at value: " + oRegion.YValue.ToString + "');" & Chr(34) & _
" alt=" & Chr(34) & oRegion.SeriesName & " value=" & oRegion.YValue & Chr(34) & ">" & _
vbCrLf
sImageMap = sImageMap & sArea
Next
Return sImageMap
End Function