3D Rotation

This post starts with the simple 3D model example from the first 3D post but with the camera moved back to its original position.

<Grid Background="AliceBlue">
   <Viewport3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <GeometryModel3D>
               <GeometryModel3D.Geometry>
                  <MeshGeometry3D>
                     <MeshGeometry3D.Positions>-0.5, -0.5, -0.5  0.5, -0.5, -0.5  0.5, 0.5, -0.5  -0.5, 0.5, -0.5</MeshGeometry3D.Positions>
                     <MeshGeometry3D.TriangleIndices>0 1 2 2 3 0</MeshGeometry3D.TriangleIndices>
                  </MeshGeometry3D>
               </GeometryModel3D.Geometry>
               <GeometryModel3D.Material>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Maroon</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.Material>
               <GeometryModel3D.BackMaterial>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Blue</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.BackMaterial>
            </GeometryModel3D>
         </ModelVisual3D.Content>
      </ModelVisual3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <AmbientLight Color="White" />
         </ModelVisual3D.Content>
      </ModelVisual3D>
      <Viewport3D.Camera>
         <PerspectiveCamera>
            <PerspectiveCamera.LookDirection>0,0,-1</PerspectiveCamera.LookDirection>
            <PerspectiveCamera.Position>0,0,2</PerspectiveCamera.Position>
            <PerspectiveCamera.FieldOfView>90</PerspectiveCamera.FieldOfView>
         </PerspectiveCamera>
      </Viewport3D.Camera>
   </Viewport3D>
</Grid>

We want to rotate the Model around the Y axis, represented by the "1" in the definition of AxisAngleRotation3D.Axis below. Because the Model has a negative Z coordinate (-0.5) the Z component will gradually increase until the angle of rotation is 180 degrees at which point the Z coordinate becomes 0.5. Because the Z coordinate is closer to use the Model will appear larger.

<Grid Background="AliceBlue">
   <Viewport3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <GeometryModel3D>
               <GeometryModel3D.Geometry>
                  <MeshGeometry3D>
                     <MeshGeometry3D.Positions>-0.5, -0.5, -0.5  0.5, -0.5, -0.5  0.5, 0.5, -0.5  -0.5, 0.5, -0.5</MeshGeometry3D.Positions>
                     <MeshGeometry3D.TriangleIndices>0 1 2 2 3 0</MeshGeometry3D.TriangleIndices>
                  </MeshGeometry3D>
               </GeometryModel3D.Geometry>
               <GeometryModel3D.Material>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Maroon</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.Material>
               <GeometryModel3D.BackMaterial>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Blue</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.BackMaterial>
            </GeometryModel3D>
         </ModelVisual3D.Content>

         <ModelVisual3D.Transform>
            <RotateTransform3D>
               <RotateTransform3D.Rotation>
                  <AxisAngleRotation3D>
                     <AxisAngleRotation3D.Axis>0,1,0</AxisAngleRotation3D.Axis>
                     <AxisAngleRotation3D.Angle>0</AxisAngleRotation3D.Angle>
                  </AxisAngleRotation3D>
               </RotateTransform3D.Rotation>
            </RotateTransform3D>
         </ModelVisual3D.Transform>

      </ModelVisual3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <AmbientLight Color="White" />
         </ModelVisual3D.Content>
      </ModelVisual3D>
      <Viewport3D.Camera>
         <PerspectiveCamera>
            <PerspectiveCamera.LookDirection>0,0,-1</PerspectiveCamera.LookDirection>
            <PerspectiveCamera.Position>0,0,2</PerspectiveCamera.Position>
            <PerspectiveCamera.FieldOfView>90</PerspectiveCamera.FieldOfView>
         </PerspectiveCamera>
      </Viewport3D.Camera>
   </Viewport3D>
</Grid>

Starting with an Angle of 0 (zero) degrees gives the same result as previously. Increasing the Angle to more than 90 degrees the reverse side of the Model comes into view.

<Grid Background="AliceBlue">
   <Viewport3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <GeometryModel3D>
               <GeometryModel3D.Geometry>
                  <MeshGeometry3D>
                     <MeshGeometry3D.Positions>-0.5, -0.5, -0.5  0.5, -0.5, -0.5  0.5, 0.5, -0.5  -0.5, 0.5, -0.5</MeshGeometry3D.Positions>
                     <MeshGeometry3D.TriangleIndices>0 1 2 2 3 0</MeshGeometry3D.TriangleIndices>
                  </MeshGeometry3D>
               </GeometryModel3D.Geometry>
               <GeometryModel3D.Material>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Maroon</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.Material>
               <GeometryModel3D.BackMaterial>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Blue</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.BackMaterial>
            </GeometryModel3D>
         </ModelVisual3D.Content>
         <ModelVisual3D.Transform>
            <RotateTransform3D>
               <RotateTransform3D.Rotation>
                  <AxisAngleRotation3D>
                     <AxisAngleRotation3D.Axis>0,1,0</AxisAngleRotation3D.Axis>

                     <AxisAngleRotation3D.Angle>120</AxisAngleRotation3D.Angle>

                  </AxisAngleRotation3D>
               </RotateTransform3D.Rotation>
            </RotateTransform3D>
         </ModelVisual3D.Transform>
      </ModelVisual3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <AmbientLight Color="White" />
         </ModelVisual3D.Content>
      </ModelVisual3D>
      <Viewport3D.Camera>
         <PerspectiveCamera>
            <PerspectiveCamera.LookDirection>0,0,-1</PerspectiveCamera.LookDirection>
            <PerspectiveCamera.Position>0,0,2</PerspectiveCamera.Position>
            <PerspectiveCamera.FieldOfView>90</PerspectiveCamera.FieldOfView>
         </PerspectiveCamera>
      </Viewport3D.Camera>
   </Viewport3D>
</Grid>

The rotation can be animated by applying a DoubleAnimation to the RotateTransform.
Reset the Angle to zero, name the AxisAngleRotation3D and add a Grid.Trigger to start the animation.

<Grid Background="AliceBlue">
   <Viewport3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <GeometryModel3D>
               <GeometryModel3D.Geometry>
                  <MeshGeometry3D>
                     <MeshGeometry3D.Positions>-0.5, -0.5, -0.5  0.5, -0.5, -0.5  0.5, 0.5, -0.5  -0.5, 0.5, -0.5</MeshGeometry3D.Positions>
                     <MeshGeometry3D.TriangleIndices>0 1 2 2 3 0</MeshGeometry3D.TriangleIndices>
                  </MeshGeometry3D>
               </GeometryModel3D.Geometry>
               <GeometryModel3D.Material>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Maroon</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.Material>
               <GeometryModel3D.BackMaterial>
                  <DiffuseMaterial>
                     <DiffuseMaterial.Brush>Blue</DiffuseMaterial.Brush>
                  </DiffuseMaterial>
               </GeometryModel3D.BackMaterial>
            </GeometryModel3D>
         </ModelVisual3D.Content>
         <ModelVisual3D.Transform>
            <RotateTransform3D>
               <RotateTransform3D.Rotation>
                  <AxisAngleRotation3D  x:Name="Rotate">
                     <AxisAngleRotation3D.Axis>0,1,0</AxisAngleRotation3D.Axis>

                     <AxisAngleRotation3D.Angle>0</AxisAngleRotation3D.Angle>

                  </AxisAngleRotation3D>
               </RotateTransform3D.Rotation>
            </RotateTransform3D>
         </ModelVisual3D.Transform>
      </ModelVisual3D>
      <ModelVisual3D>
         <ModelVisual3D.Content>
            <AmbientLight Color="White" />
         </ModelVisual3D.Content>
      </ModelVisual3D>
      <Viewport3D.Camera>
         <PerspectiveCamera>
            <PerspectiveCamera.LookDirection>0,0,-1</PerspectiveCamera.LookDirection>
            <PerspectiveCamera.Position>0,0,2</PerspectiveCamera.Position>
            <PerspectiveCamera.FieldOfView>90</PerspectiveCamera.FieldOfView>
         </PerspectiveCamera>
      </Viewport3D.Camera>
   </Viewport3D>

   <Grid.Triggers>
      <EventTrigger RoutedEvent="Grid.MouseDown">
         <BeginStoryboard>
            <Storyboard>
               <DoubleAnimation From="0"
                                To="360"
                                BeginTime="0:0:0"
                                Duration="0:0:4"
                                Storyboard.TargetName="Rotate"
                                Storyboard.TargetProperty="Angle" />
            </Storyboard>
         </BeginStoryboard>
      </EventTrigger>
   </Grid.Triggers>

</Grid>