title: Finding a minimum bounding sphere for a frustum
body: <p>I have a frustum (truncated pyramid) and I need to compute a bounding sphere for this frustum that's as small as possible. I can choose the centre to be right in the centre of the frustum and the radius be the distance to one of the "far" corners, but that usually leaves quite a lot of slack around the narrow end of the frustum</p>
  
  <p>This seems like simple geometry, but I can't seem to figure it out. Any ideas?</p>