Shane Arpas Shane Arpas - 7 months ago 122
Vb.net Question

Chart annotations: How can I align the annotation along an axis of a datapoint

I have aligned the annotations to data points; I want to align the annotations vertically.

I have read this, But can't figure out how to relate the chart width to data points. https://msdn.microsoft.com/en-us/library/dd456731.aspx

And this: MS Charting Annotations refuse to align to mouse position

I added a picture of the chart so far as an example.



'create new chart
chart1 = New DataVisualization.Charting.Chart

'add chart areas
chart1.ChartAreas.Add("NewChartArea")
chart1.ChartAreas("NewChartArea").Area3DStyle.Enable3D = False
chart1.ChartAreas("NewChartArea").AxisX.MajorGrid.Enabled = False 'turn chart background grid on and off
chart1.ChartAreas("NewChartArea").AxisY.MajorGrid.Enabled = False 'turn chart background grid on and off
chart1.ChartAreas("NewChartArea").AxisX.Title = "Activities of daily living" '----> title on the bottom for the x axis
'[template] chart1.ChartAreas("NewChartArea").AxisX.LabelStyle.Angle = 45
'[template] Chart1.Series(SeriesZeroChartName).Label = " my own label" ' -----> adds a label at the top of each bar

For c As Integer = 2 To Me.DataGridViewResultsAdls.ColumnCount - 1

Dim NextSeriesChartName As String
NextSeriesChartName = DataGridViewResultsAdls.Columns(c).Name

chart1.Series.Add(NextSeriesChartName)
chart1.Series(NextSeriesChartName).ChartType = DataVisualization.Charting.SeriesChartType.Bar 'CHART CHANGER ****** change this value to change chart type
chart1.Series(NextSeriesChartName).Points.Clear()
chart1.Series(NextSeriesChartName).IsValueShownAsLabel = True '----> puts little labels ontop of each bar
chart1.Series(NextSeriesChartName).SmartLabelStyle.Enabled = True


' fill each subsequent series with points
For Count As Integer = 0 To DataGridViewResultsAdls.Rows.Count - 2
Dim NextColumnName As String
NextColumnName = DataGridViewResultsAdls.Columns(c).Name

' define X values
Dim XLabelMyCustom As String
XLabelMyCustom = DataGridViewResultsAdls.Item(0, Count).Value
'define Y values
Dim YLabelMyCustom As String
YLabelMyCustom = DataGridViewResultsAdls.Item(NextColumnName, Count).Value

' add the point to the chart
chart1.Series(NextSeriesChartName).Points.AddXY(XLabelMyCustom, YLabelMyCustom)

' create custom labels for the x axis
chart1.ChartAreas("NewChartArea").AxisX.CustomLabels.Add(Count + 0.5, Count + 0.4 + 0.5, "Q2", 0, DataVisualization.Charting.LabelMarkStyle.None)
chart1.ChartAreas("NewChartArea").AxisX.CustomLabels.Add(Count + 0.5 + 0.5, Count + 0.9 + 0.5, "Q1", 0, DataVisualization.Charting.LabelMarkStyle.None)
chart1.ChartAreas("NewChartArea").AxisX.CustomLabels.Add(Count + 0.5, Count + 1, "Q3", 2, DataVisualization.Charting.LabelMarkStyle.LineSideMark)



'Create a variable MyDataPoint to hold the current datapoint
Dim MyDataPoint As DataPoint
MyDataPoint = chart1.Series(NextSeriesChartName).Points(Count)
'Create a new text annotation
Dim MyTextAnnotation As TextAnnotation
MyTextAnnotation = New TextAnnotation
MyTextAnnotation.Text = "some notation"
'[template] MyTextAnnotation.X = <---- sets coordinates on screen for x
'[template ]MyTextAnnotation.Y = <---- sets coordinates on screen for y
'[template] MyTextAnnotation.AnchorDataPoint = MyDataPoint 'sets the point where the notation will be
'[template] chart1.Annotations.Add(MyTextAnnotation) ' adds the notation to the chart

' only add annotations to the chart once per series
If c = 2 Then
MyTextAnnotation.AxisY = chart1.ChartAreas("NewChartArea").AxisY

' [template] chart1.Series(NextSeriesChartName).Points.Item(Count).ToString <--- output points to a string {x,y}


MyTextAnnotation.AnchorDataPoint = MyDataPoint 'sets the point where the notation will be
chart1.Annotations.Add(MyTextAnnotation) ' adds the notation to the chart
MyTextAnnotation.AnchorOffsetX = -10


End If
Next

Next

'Add chart to control and set dock to fill
Me.PanelChartAdls.Controls.Add(chart1)
chart1.Dock = DockStyle.Fill

End If

TaW TaW
Answer

Positioning in a Chart control is rather complex.

To begin with a chart has three coordinate systems:

  • The data values
  • Percentages of some area, most notably the ChartArea and the InnerPlotPosition
  • Pixels of the Chart control's ClientArea

The simplest way to achieve an alignment of your Annotations is to first anchor each to its DataPoint:

MyTextAnnotation.AnchorDataPoint = MyDataPoint 

Next you override the X-Position to a value you like:

MyTextAnnotation.X = someValue;

A few notes:

  • While by default the Annotation.Position would use percentages, after anchoring it to a DataPoint it uses the values instead. So using 50 would not place in somewhere around the middle but all to the right...

Looking at your Chart I suggest using a value of 3.

  • If your values vary this positioning will also vary. And when you resize the Chart the Axes will be resized and the Annotations will move as well.

Btw: The percentages are in relation to the next outer container: The ChartAreas to the Chart.ClientRectangle, the InnerPlotPostion to the ChartArea and each element to the container it is docked to..

  • The Positions are by default set to automatic so their values are NaN. To access the (current) values you can call ElementPosition.ToRectangleF().

  • Also note that there are several functions on the Chart's Axes that will convert values, pixels and percent-positions.

However you need to find a valid moment to call them; if the Chart is not done with its layout, they will return null.

You can either call them in one the the three Paint events or in response to a user interaction like a Mouse event.

Here is how to use them for positioning all Annotations to a (somewhat) fixed pixel position:

private void chart1_PostPaint(object sender, ChartPaintEventArgs e)
{
    Axis AY = chart1.ChartAreas[0].AxisY;

    double pypx = AY.ValueToPosition(AY.PixelPositionToValue(30));

    foreach (TextAnnotation ta in chart1.Annotations)
    {
        ta.X = pypx;
    }
}

Now the Annotations will not move when the chart is resized or when the data values grow or shrink. At least not a lot; a few jumps can be seen. Either because I missed something or because of rounding issues.

But I suggest going with the simpler method of setting their X-Position to a fixed value on your axis..:

MyTextAnnotation.X = 3;

This would put them at the yellow line you drew.