Viewport3D ModelVisuals3D not visible when inside

Question

If I put viewport3D inside Canvas my viewport3D is not visible anymore. If I remove Canvas then Viewport3D is visible again. What I'm doing wrong?

          <Canvas  Width="900" Height="524">
            <Viewport3D Name="mainViewport" ClipToBounds="True" HitTestVisible="False">
                        <Viewport3D.Camera>
                            <PerspectiveCamera 
                              FarPlaneDistance="3500"
                              LookDirection="0,0,1"
                              UpDirection="0,1,0"
                              NearPlaneDistance="1" 
                              Position="0,0,0" 
                              FieldOfView="66" />
                        </Viewport3D.Camera>
                        <ModelVisual3D>
                            <ModelVisual3D.Content>
                                <AmbientLight Color="White" />
                            </ModelVisual3D.Content>
                        </ModelVisual3D>
                    </Viewport3D>
            </Canvas>

Answer 1

I think the ViewPort3D will end up in the upper left corner of the Canvas with a Width and Height of 0 since Canvas never stretches its Children. Try to add Canvas.Left and Canvas.Top at the positioning of your choise and then add Width and Height for your Viewport3D. If you want your Viewport3D to always fill the available space then Canvas is the wrong way to go.

<Canvas Width="900" Height="524">
    <Viewport3D Canvas.Left="100"
                Canvas.Top="100"
                Width="200"
                Height="200"
                Name="mainViewport"
                ClipToBounds="True" 
                IsHitTestVisible="False">
        <Viewport3D.Camera>
            <PerspectiveCamera  
                        FarPlaneDistance="3500" 
                        LookDirection="0,0,1" 
                        UpDirection="0,1,0" 
                        NearPlaneDistance="1"  
                        Position="0,0,0"  
                        FieldOfView="66" />
        </Viewport3D.Camera>
        <ModelVisual3D>
            <ModelVisual3D.Content>
                <AmbientLight Color="White" />
            </ModelVisual3D.Content>
        </ModelVisual3D>
    </Viewport3D>
</Canvas>