在视口wpf中鼠标单击时获取坐标

Question

我想在视口中返回鼠标单击的坐标。当我在视口内部单击时，它显示我的屏幕坐标（例如480,650），但我的视口的范围是（0,0）说（10,10）。如何获取鼠标点击视口坐标系的坐标。 我的xaml代码：

    <Window x:Class="PathOptimization.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Geometries"
    xmlns:tool3d="clr-namespace:_3DTools;assembly=3DTools"
    Title="MainWindow" Height="350" Width="1000" WindowState="Maximized">
    <Grid  x:Name="grdView" >
    <Grid.ColumnDefinitions >
        <ColumnDefinition Width="200"></ColumnDefinition>
        <ColumnDefinition></ColumnDefinition>
        <ColumnDefinition Width="200"></ColumnDefinition>
    </Grid.ColumnDefinitions>        
    <Viewport3D x:Name="viewport" Grid.Column="1" MouseDown="button_MouseDown"   Margin="0,35,0,0">
        <ContainerUIElement3D>
            <ModelUIElement3D >
        ..............................            
            </ModelUIElement3D>
       </ContainerUIElement3D>
   <Viewport3D.Camera>
    <PerspectiveCamera Position="0,1,9"
    LookDirection="0,0,-2"
    UpDirection="0,1,0"/>
  </Viewport3D.Camera>
  </Viewport3D>

当我点击视口内的屏幕时，我得到了屏幕坐标。如何获取相对于视口的坐标。

private void button_MouseDown(object sender, MouseButtonEventArgs e)
    {
        Point pointToWindow = e.GetPosition(viewport);
        Point pointToScreen = PointToScreen(pointToWindow);
        double x = (pointToScreen.X);
        double y = (pointToScreen.Y);
        MessageBox.Show(x + "," + y);
    }