Reading axis range after auto-scale

[thbu]

Hi,

I'm using TChart with multiple Y-axis and TAutoScaleAxisTransform for auto-scale. How can I find out the minimum and maximum value of each axis that after auto-scaling is done?
To clarify, I do not mean an event that is executed after autoscaling, but simply a way to read the auto-scaled min/max of each axis.

[arneolav]

Try: ..Series.GetMax

[wp]

You probably mean the range in axis units (i.e. units of the user data)? In graph units, with autoscale transformation, the axis values range between the MinValue and MaxValue specified by the AutoScaleAxisTransform. In order to get them in in axis units, you have to apply the method GraphToAxis of the axistransformation which, in turn, you get from the method GetTranform of the axis.

The following procedure is rather general, it also handles the case that no autoscale transformation is used:

Code: Pascal  [Select][+][-]

1. uses
2.   TAChartUtils;
3.  
4. procedure GetAxisRange(Axis: TChartAxis; var AMin, AMax: Double);
5. var
6.   t: TAxisTransform;
7.   at: TChartAxisTransformations;
8.   ext: TDoubleRect;
9.   chart: TChart;
10. begin
11.   chart := Axis.Arrow.GetOwner as TChart;
12.   at := Axis.GetTransform;
13.  
14.   for t in at.List do
15.     if t is TAutoscaleAxisTransform then
16.     begin
17.       AMin := at.GraphToAxis(TAutoscaleAxisTransform(t).MinValue);
18.       AMax := at.GraphToAxis(TAutoscaleAxisTransform(t).MaxValue);
19.       exit;
20.     end;
21.  
22.   // No autoscale transform available
23.   ext := chart.LogicalExtent;
24.   if Axis.IsVertical then
25.   begin
26.     AMin := at.GraphToAxis(ext.a.Y);
27.     AMax := at.GraphToAxis(ext.b.Y);
28.   end else
29.   begin
30.     AMin := at.GraphToAxis(ext.a.X);
31.     AMax := at.GraphToAxis(ext.b.X);
32.   end;
33. end;  

I added this to the Chart Runtime FAQ wiki: https://wiki.freepascal.org/TAChart_Runtime_FAQ#How_to_find_the_range_of_values_covered_by_an_axis

[thbu]

Thank you. It works very well.