Hi Changmin,
The following code shows how to transform from view to polar coordinate:
NPolarChart polarChart = (NPolarChart)nChartControl1.Charts[0];
NPointF modelPoint = polarChart.TransformViewToRadialModel(new Nevron.GraphicsCore.NPointF(e.X, e.Y));
double value = polarChart.Axis(StandardAxis.PolarAngle).Scale.Ruler.ScaleToLogical(modelPoint.X);
double angle = polarChart.Axis(StandardAxis.Polar).Scale.Ruler.ScaleToLogical(modelPoint.Y);
We hope this helps - let us know if you have any questions.
Best Regards,
Nevron Support Team