<GeometryModel3D>
<GeometryModel3D.Geometry>
<MeshGeometry3D
Positions="-1 -1 0 1 -1 0 -1 1 0 1 1 0"
Normals="0 0 1 0 0 1 0 0 1 0 0 1"
TextureCoordinates="0 1 1 1 0 0 1 0 "
TriangleIndices="0 1 2 1 3 2" />
</GeometryModel3D.Geometry>
<GeometryModel3D.Material>
<DiffuseMaterial>
<DiffuseMaterial.Brush>
<SolidColorBrush Color="Cyan" Opacity="0.3"/>
</DiffuseMaterial.Brush>
</DiffuseMaterial>
</GeometryModel3D.Material>
<!-- Translate the plane. -->
<GeometryModel3D.Transform>
<TranslateTransform3D
OffsetX="2" OffsetY="0" OffsetZ="-1" >
</TranslateTransform3D>
</GeometryModel3D.Transform>
</GeometryModel3D>