Overlapping points | Infragistics Forums

Here is just one way of going about it. Other ways involve translating from the clicked point back to axis values and examining the data source bound to the series for the closest points, but this way lets you deal with pixel values which is what you are most concerned with seeing as how the problem is when the points are occluding each other.

You can adjust the nearness value to control how close the points need to be in pixel distance before being pulled into the list. I did this in Silverlight before noticing you were doing WPF there. You may need to set the grid containing the chart as the PlacementTarget of the popup in WPF before this works there, or something of that nature.

<UserControl.Resources>
        <local:TestData x:Key="data" />
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid x:Name="chartContainer">
            <igChart:XamDataChart x:Name="theChart"
                              SeriesMouseLeftButtonUp="theChart_SeriesMouseLeftButtonUp">
                <igChart:XamDataChart.Axes>
                    <igChart:NumericXAxis x:Name="xAxis" />
                    <igChart:NumericYAxis x:Name="yAxis" />
                </igChart:XamDataChart.Axes>
                <igChart:XamDataChart.Series>
                    <igChart:ScatterSeries x:Name="scatter"
                    XAxis="{Binding ElementName=xAxis}"
                    YAxis="{Binding ElementName=yAxis}"
                    XMemberPath="X"
                    YMemberPath="Y"
                    ItemsSource="{StaticResource data}" />
                </igChart:XamDataChart.Series>
            </igChart:XamDataChart>

            <Popup x:Name="thePopup" IsOpen="False">
                <Border Background="White" BorderThickness="1" BorderBrush="Gray">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition />
                            <ColumnDefinition Width="Auto" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto" />
                            <RowDefinition />
                        </Grid.RowDefinitions>

                        <TextBlock Text="X" Grid.Row="0" Grid.Column="1" MouseLeftButtonUp="TextBlock_MouseLeftButtonUp"/>
                        <ItemsControl ItemsSource="{Binding}" Grid.Row="1"
                                      Margin="5">
                            <ItemsControl.ItemTemplate>
                                <DataTemplate>
                                    <StackPanel Orientation="Horizontal">
                                        <ContentControl ContentTemplate="{Binding Series.LegendItemBadgeTemplate}"
                                                    Content="{Binding}" />
                                        <TextBlock Text="X=" />
                                        <TextBlock Text="{Binding Item.X}" />
                                        <TextBlock Text=", Y=" />
                                        <TextBlock Text="{Binding Item.Y}" />
                                    </StackPanel>
                                </DataTemplate>
                            </ItemsControl.ItemTemplate>
                        </ItemsControl>
                    </Grid>
                </Border>
            </Popup>
        </Grid>
    </Grid>

And the code behind:

public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }


        private const double Nearness = 10.0;
        
        private void theChart_SeriesMouseLeftButtonUp(
            object sender, 
            DataChartMouseButtonEventArgs e)
        {
            Point pos = e.GetPosition(chartContainer);
            var hitItems = GetHitItems(e);

            thePopup.DataContext = hitItems;
            thePopup.HorizontalOffset = pos.X;
            thePopup.VerticalOffset = pos.Y;
            thePopup.IsOpen = true;
        }

        private List<DataContext> GetHitItems(DataChartMouseButtonEventArgs e)
        {
            if (e.Series == null || e.Item == null)
            {
                return new List<DataContext>();
            }
            var markers =
                from marker in e.Series
                    .VisualDescendantsOfType<Marker>()
                where marker.Visibility == Visibility.Visible
                select marker;

            var hit =
                (from marker in markers
                 where marker.Content is DataContext &&
                 (marker.Content as DataContext).Item == e.Item &&
                 (marker.Content as DataContext).Series == e.Series
                 select marker).FirstOrDefault();

            if (hit == null)
            {
                return new List<DataContext>();
            }

            var hitPoint = hit.TransformToVisual(e.Series)
                .Transform(new Point(0, 0));

            var markerPositions =
                from marker in markers
                select new Tuple<Marker, Point>(
                    marker, marker.TransformToVisual(e.Series)
                    .Transform(new Point(0, 0)));

            var nearnessSquared = Nearness * Nearness;

            var closeMarkers =
                from markerAndPos in markerPositions
                where Math.Pow(markerAndPos.Item2.X - hitPoint.X, 2) +
                    Math.Pow(markerAndPos.Item2.Y - hitPoint.Y, 2) 
                    < nearnessSquared
                orderby Math.Pow(markerAndPos.Item2.X - hitPoint.X, 2) +
                    Math.Pow(markerAndPos.Item2.Y - hitPoint.Y, 2)
                select markerAndPos.Item1;

            List<DataContext> items =
                (from marker in closeMarkers
                 where marker.Content is DataContext
                 select marker.Content as DataContext)
                .ToList();

            return items;
        }

        private void TextBlock_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            thePopup.IsOpen = false;
        }
    }

    public static class VisualTree
    {
        public static IEnumerable<DependencyObject> VisualDescendants(
            this DependencyObject parent)
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
            {
                var current = VisualTreeHelper.GetChild(parent, i);

                yield return current;
                foreach (var child in current.VisualDescendants())
                {
                    yield return child;
                }
            }
        }

        public static IEnumerable<T> VisualDescendantsOfType<T>(

            this DependencyObject parent)
        {
            return parent.VisualDescendants().OfType<T>();
        }
    }



    public class TestData
        : ObservableCollection<TestDataItem>
    {
        public TestData()
        {
            Add(new TestDataItem() { X = 1, Y = 1 });
            Add(new TestDataItem() { X = 2, Y = 2 });
            Add(new TestDataItem() { X = 3, Y = 3 });
            Add(new TestDataItem() { X = 3.01, Y = 3.01 });
            Add(new TestDataItem() { X = 3.02, Y = 3.02 });
            Add(new TestDataItem() { X = 4, Y = 4 });
            Add(new TestDataItem() { X = 5, Y = 5 });
            Add(new TestDataItem() { X = 6, Y = 6 });
        }
    }

    public class TestDataItem
    {
        public double X { get; set; }
        public double Y { get; set; }
    }

-Graham