[RadChartView] PieTwoLabelColumnsStrategy - DistanceBetweenLabels not working properly

[Jérôme]

Hi,

I'm using Telerik for Winforms 2023.3.1010 on .NET 7.

While trying to configure the position of my label position using PieTwoLabelColumnsStrategy, only the first label seems to be working with DistanceBetweenLabels property.

 

 PieTwoLabelColumnsStrategy strategy = new PieTwoLabelColumnsStrategy()
 {
     DistanceBetweenLabels = 50,
     DistanceToLabel = -100
 };

 SmartLabelsController smartLabelsController = new SmartLabelsController
 {
     Strategy = strategy
 };

 radChartView.Controllers.Add(smartLabelsController);
 radChartView.ShowSmartLabels = true;

Here is how I'm filling the chart:

   radChartView.AreaType = ChartAreaType.Pie;
   radChartView.Series.Clear();

   DonutSeries donut = new DonutSeries
   {
       ShowLabels = true,
       LabelMode = PieLabelModes.Horizontal,
       DrawLinesToLabels = true,
       SyncLinesToLabelsColor = true,
       NumberOfColors = categoryCount
   };

   foreach (var v in totals.OrderByDescending(s => s.Statut))
   {
       PieDataPoint point = new PieDataPoint(v.Nombre, v.Statut)
       {
           Label = $"{v.Percentage}% {v.Statut}"
       };

       donut.DataPoints.Add(point);
   }

   radChartView.Series.Add(donut);
   radChartView.Area.View.Palette = KnownPalette.Metro;
   radChartView.SelectionMode = ChartSelectionMode.SingleDataPoint;
   radChartView.BackColor = Color.WhiteSmoke;

With small percentages, it doesn't work (except of the right bottom label)

With higher percentages it seems to be working :

The behavior is quite inconsistent.

Thank you for your help.

 

[Dinko | Tech Support Engineer]

Hello Jérôme,

Thank you for the provided details.

To test your case, I have created a sample project using the provided code snippets. So far I wasn't able to observe the described behavior. Could it be possible to modify my test project to reproduce this behavior and send it back to me so that I can debug it on my side and try to find a suitable solution? Also, in your post, you mentioned that "With higher percentages, it seems to be working". Can you elaborate more on what you mean by "higher percentages"? Do you mean that the labels are okay on higher DPI? If yes, what is the current resolution of them monitor when you start the application and what is the resolution when the labels are positioned correctly?

I am looking forward to your reply.

Regards,
Dinko | Tech Support Engineer
Progress Telerik

[Jérôme]

Hi Dinko,

I'm able to reproduce my issue. I've adjusted your code, changing the databinding part.

With this code, the labels are not evenly spaced between them. I'm wondering if it's because of the very low percentages.

The more you increase DistanceBetweenLabels property, the more visible it becomes.

Thank you for your help.

Regards

[Dinko | Tech Support Engineer]

I appreciate your effort in updating the project to reproduce the described behavior. I have examined this behavior and see what you mean here. When the smart labels strategy is set, it will target the labels that are overlapping. With this in hand, the value in the DistanceBetweenLabels property will be used for labels that overlap. It will not be used to set the distance between all labels. In this particular case, the orange label (United States) does not move which makes it static as it does not overlap with any other label. The distance between the next label (Spain) will vary depending on the height of the pie series. 

I have forwarded this behavior to the development team for further investigation. Upon brief discussion, we agree that this is more of a corner case. Basically, setting a big value to the DistanceBetweenLabels won't be valid as it will move the labels outside the chart area. Using a big value for this property with the combination of data points with very close values will lead to an undesirable visual result. My recommendation will be to set a value to the DistanceBetweenLabels which most fit your case. The labels in any case won't overlap, however, the value between the labels that are overlapping by default should not increase the height of the chart component.

I hope that my reply sheds some light on this behavior.

[Jérôme]

Thank you for clarifying this component's behavior. Maybe the documentation of ChartView could be updated to explain the interest of DistanceBetweenLabels property when using a SmartLabelsController.

Regards

[Dinko | Tech Support Engineer]

You have a point here. I have double-checked the documentation and indeed this property is not mentioned. I have logged an internal task to update the Smart labels help article and provide more information regarding the build strategies and their properties.

I have updated your Telerik Points for bringing this to our attention.

[Jérôme]

Thank you !