Thank you for providing more details on the matter. We understand that having a simple IsVisible property would make this a bit easier.
There is more than one way to get the behavior you need. I can suggest two approaches that will help you determine whether a point is in the visible range.
The first approach assumes you are using a point template. If you are not using a point template and if you are using line series this is not applicable. If you were using a different series (one that has default visuals, like point series) we could tweak the code to make it work.
The first approach involves looking in the visual tree and looking up the visible elements. These visible elements (ContentPresenter in the case of PointTemplate) are the data point presenters. Each visual element contains the data point (in the DataContext). Simply, if a visual element is visible - its associated data point is in the visible range.
The second approach essentially iterates all data points and asks the plot area to calculate whether it contains the point. Both the plot-area and data-point's layout-slot are RadRect objects, so simple rect intersection calculations are done.
I hope that you will find at least one of these solutions to be feasible. Let us know if you need more information.
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