HelixToolkit how to exclude elements from HitTest
<p>I have a scene with a skybox and I would like to get the point the user clicked projected onto the skybox.</p>

<p>I'm using <code>HelixViewport3D.FindNearestPoint(Point pt)</code> to get the point, which works very well, except when there's anything between the click and the skybox. In this situation it returns the point projected onto the object in front of the skybok. </p>

<p>Is there any way to flag an element so it would be ignored in HitTests?</p>