As Eric Sink pointed out recently, "WPF 3D doesn't know how to draw lines." . Fortunately, the WPF 3D team at Microsoft has made available the 3DTools library that includes the ScreenSpaceLines3D class that derives from ModelVisual3D and draws lines in a 3D scene. The "screen space" in the name of this class indicates that you specify the thickness of the lines in terms of device-independent units, which are 1/96th inch and hence often pixels. What's really nice is that the source code to ScreenSpaceLines3D is also available so you can see the clever techniques at work to make this happen: Basically, each line is a pair of triangles arranged in a long thin rectangle. While you specify the begin point and end point of this "line" in 3D coordinates, the ScreenSpaceLines3D class must determine the thickness of this "line" at each end so that after the various transforms have been applied to it (including the camera transforms — see Chapter 7 of my book 3D Programming for Windows ) it Read More...