Multiple y-axes on a graphing/charting component

[Stretchwickster]

Hi,

At the moment I have a TChart component with 1 x-axis and 1 y-axis on which I display 3 series. Each series has a different scale (e.g. Series1 0..5, Series2 0..2, Series3 0..1). Ideally, what I want to do is display 3 y-axes and 1 x-axis so that each y-axis has the relevant scale for its particular Series (if that makes sense!!!). Any suggestions?

P.S. Below is a crude little diagram!!
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3 y-axes --> |||
|||________________ <-- 1 x-axis

 

[Roderich]

try Chart.ChartGetAxisLabel, this will give you the possibility to modify the axis labels.
Then you can write all 3 y axis texts.

This is not nice but as far as i know you can only have one y axis in a TChart.

Roderich

 

[LucieLastic]

hi

I think 2 y axis is the max. I have used a TDBChart(derives from TChart) and added 2 series to one graph. I think if you want to add more than 3 you have to assign them to one of the Y axis and it adjusts to a range suitable for both series.

I've copied and pasted my proc which does this:

procedure TBase.AddSeriesToGraph(sLabel : string; xSelField : Tfield; ySelField : Tfield);
var NewSeries : TLineSeries;
MsgRes : TModalResult;
begin
Application.ProcessMessages;
NewSeries := TLineSeries.Create(self);
NewSeries.ParentChart := OvlGraph.Chart;
NewSeries.DataSource := Query;
NewSeries.CheckDataSource;
NewSeries.LinePen.Width := 2;
NewSeries.SeriesColor := RGB(Random(256), Random(256),Random(256));

OvlGraph.Chart.RightAxis.Increment := 0.0001;
OvlGraph.Chart.LeftAxis.Increment := 0.0001;

if OvlGraph.Chart.SeriesCount > 2 then
begin
MsgRes := MessageDlg('Scale to Left Axis or Right Axis ? (Yes = Left, No = Right)',
mtConfirmation,[mbyes,mbno, mbCancel],0);
if MsgRes = MRCancel then
begin
NewSeries.Free;
Exit;
end;
if MsgRes = mrYes then
begin
NewSeries.VertAxis := aLeftAxis;
NewSeries.YValues.ValueSource := ySelField.FieldName;
end
else
begin //result = mrNo
NewSeries.VertAxis := aRightAxis;
OvlGraph.Chart.RightAxis.LabelsOnAxis := true;
NewSeries.YValues.ValueSource := ySelField.FieldName;
end;
Application.ProcessMessages;
end;

if OvlGraph.Chart.SeriesCount = 1 then
begin
NewSeries.VertAxis := aLeftAxis;
NewSeries.YValues.ValueSource := ySelField.FieldName;
OvlGraph.Chart.LeftAxis.Title.Caption := ySelField.FieldName;
NewSeries.SeriesColor := RGB(Random(100)+100, Random(100)+100,Random(100)+100);
Application.ProcessMessages;
end;

if OvlGraph.Chart.SeriesCount = 2 then
begin
NewSeries.SeriesColor := RGB(Random(100)+20, Random(100)+20,Random(100)+20);
if OvlGraph.Chart.RightAxis.Title.Caption = '' then
begin
NewSeries.VertAxis := aRightAxis;
OvlGraph.Chart.RightAxis.LabelsOnAxis := true;
NewSeries.YValues.ValueSource := ySelField.FieldName;
OvlGraph.Chart.RightAxis.Title.Caption := ySelField.FieldName;
end
else //insert 2nd one on the left
begin
NewSeries.VertAxis := aLeftAxis;
OvlGraph.Chart.LeftAxis.LabelsOnAxis := true;
NewSeries.YValues.ValueSource := ySelField.FieldName;
OvlGraph.Chart.LeftAxis.Title.Caption := ySelField.FieldName;
end;
Application.ProcessMessages;
end;

if xSelField.DataType = ftDateTime
then NewSeries.XValues.DateTime := true;
NewSeries.XValues.ValueSource := xSelField.FieldName;
OvlGraph.Chart.BottomAxis.Title.Caption := xSelField.FieldName;
OvlGraph.Chart.BottomAxis.Automatic := true;
OvlGraph.Chart.BottomAxis.AdjustMaxMin;
NewSeries.Title := ySelField.FieldName;

SynchRelativeScales;
Application.ProcessMessages;
OvlGraph.Chart.repaint;
Application.ProcessMessages;
end;

Hope this is helpful.

lou

 

[LucieLastic]

Feel free to tidy up and post back :->. It was my first attempt at graphs and it works, so I haven't looked at it since...

 

[Stretchwickster]

Roderich:

I can't find either

 Chart.ChartGetAxisLabel

or

 Chart.GetAxisLabel

I don't think it will really help to simply have 3 labels because the 3 series will be assigned to the one axis still, which means 2 graphs will be very tiny and one will be the right size (they won't be resized according to a specific axis!).

Lou:

Thanks for the muchos code you posted. But, I'm a wimp and wanna steer clear of databases for this app. I calculate all the values manually in my code and it will be too much hassle to convert them to db tables! But thanks anyway! ;-)

 

[LucieLastic]

hi Stretchwickster

No probs. I posted all the code as I think there may be some commands in there which are common to both types of charts - I think the technique will be the same. 'Fraid you'll just have to strip out the uninteresting bits.

I still think that if the scales are very different, stick the other 2 on the right hand side of the chart and adjust the axis accordingly to show optimum wotsit.

lou

 

[Roderich]

Sorry Stretchwickster, the name of the event in TChart exactly is &quot;OnGetAxisLabel&quot;.

I faced the same problem with big/small scales. I fixed it by simply calculating nice limits and then applying a factor to the series values. This factor has to be taken care of in OnGetAxisLabel event, then it works nice.