Mouse position -> data -> position are not the same values

[Martin]

hi

I have used your cross-hair example but trying to extend it and having issues

I boiled it down to the code example below

1) Get a mouse position
2) Get the data representing that position
3) For that data, get the mouse position

how can these return different values?

regards
martin

            var plotAreaPanel = sender as ClipPanel;
            var mousePosition = e.GetPosition(plotAreaPanel);
           
            var dataAtMouse = _Chart.DefaultView.ChartArea.AxisX.ConvertPhysicalUnitsToData(mousePosition.X);
            var physicalAtMouse = _Chart.DefaultView.ChartArea.AxisX.ConvertDataUnitsToPhysical(dataAtMouse);

            if (mousePosition.X != physicalAtMouse)
            {
                Debug.Assert(false, "Should never happen");
            }

[Petar Kirov]

Hi Martin,

This is a known issue. It is logged here in our Public Issue Tracker. Presently you can can workaround it the following way: 

var dataX = this.chart.DefaultView.ChartArea.AxisX.ConvertPhysicalUnitsToData(position.X);
var dataY = this.chart.DefaultView.ChartArea.AxisY.ConvertPhysicalUnitsToData(position.Y);

double xMin = _Chart.DefaultView.ChartArea.AxisX.ActualMinValue;
double yMax = _Chart.DefaultView.ChartArea.AxisY.ActualMaxValue;

var physicalX = this.chart.DefaultView.ChartArea.AxisX.ConvertDataUnitsToPhysical(dataX - xMin);
var physicalY = this.chart.DefaultView.ChartArea.AxisY.ConvertDataUnitsToPhysical(yMax - dataY);

Please note that, due to the nature of floating-point calculations,  physicalX/Y will be very close to poistion.X/Y but probably will not be equal. The error should be smaller than 10^-3. 

On as side note, you may be interested in reviewing our newer charting solution - RadChartView (represented by the RadCartesianChart, RadPolarChart and RadPieChart classes). The new control was built from the ground-up to provide significantly better performance, easy to use API and support for implicit styles. Additionally RadCartesianChart provides a built-in customizable Crosshair behavior which you can see in this online demo. A sample project demonstrating the feature is also available here in our XAML SDK on GitHub.

I hope you will find the RadChartView suitable for your project.

Regards,
Petar Kirov
Telerik