Dual axis plot
lazarus / 55-TAChart

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stellar41 · 2016-11-08 11:06

Hi,
Ive just started using Lazarus and TAChart and I have a question about
setting up a simple dual y axis plot.
 
I assumed that I could set this up in the Object inspector. 
I have Left, Bottom and Right TChartAxis items. 
I have set the properties for the Left TChartAxis as
Alignment :  calLeft
Range : Max=40 Min =-10 UseMax= True UseMin= True
Title : Temperature
For the Right TChartAxis
Alignment :  calRight
Range : Max=100 Min  = 0 UseMax= True UseMin= True
Title : Humidity

The graph displays right and left axis titles correctly.
Only right axis displays values but these are the values I set for the
left axis . 
It also still autoranges if the data is outside these values.

I just have a TAChart on the form, create the TLineSeries at run time
and add the series to the Chart.
What am I missing?

Thanks for your help.

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wp · 2016-11-08 11:33

There are step-by-step instructions for creating a dual-axis chart in
http://wiki.lazarus.freepascal.org/TAChart_Tutorial:_Dual_y_axis,_Lege
nd; a related tutorial is http://wiki.lazarus.freepascal.org/TAChart_T
utorial:_Multiple_Panes_in_one_Chart.

I think they explain what you must do - I just don't want to write
this again... But feel free to ask again if you get stuck somewhere.

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stellar41 · 2016-11-08 13:17

Sure, I didn't want to waste your time.
Id already had a look at those examples, and didn't quite see an
answer to my problem so I thought Id ask
I go through it again.
Thanks.

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wp · 2016-11-08 15:10

Add a chartAdd a second y axis to the chart, set its Alignment to
alRight. In the Object Tree you see: AxisList --> 0 - Left, 1 - Bottom
2 - RightAdd the series to the chart,For those series which will be
plotted on the left axis set their AxisIndexY to 0 (the index of the
left axis in step #2), for those to be plotted on the right axis set
their AxisIndexY to 2Add a ChartAxisTransformations component, assign
it to the LeftAxis.TransformationsDouble-click the
ChartAxisTransformations component, add an AutoScaleTransformRepeat
steps 5 and 6 with for the right axis.Using the MinValue/MaxValue of
the AutoScaleTransforms you can offset the curves: Assume a virtual
vertical axis covering the entire chart y  ranges from 0 to 1. The
Minvalue identifies the start, the Maxvalue the end of the autoscaled
series range. So, if you want to autoexand both series to the entire
axis leave the MinValue/Maxvalue of their AutoscaleAxisTransforms at 0
and 1. If you want the series of the left axis in the lower half of
the axis set its AutoscaleAxisTransform.MinValue to 0 and its Maxvalue
to 0.5; to move the series of the right axis to the upper half set its
AutoScaleAxisTransform.MinValue to 0.5 and its maxValue to 1.0.The
same topic was discussed in http://forum.lazarus.freepascal.org/index.
php/topic,30026.msg190815.html#msg190815, and maybe in other threads.
Use the forum search.

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stellar41 · 2016-11-11 12:09

Thanks wp, thats helpful.