I have been using two of the CST Berger -30mm offset prisms stacked for sometime. Chris and I often work together on jobs running two robots, and use the same backsight on occassion.
Old thread I know, but I recently thought about this, was googling keywords/phrases and saw this thread as one of my top results.
Here is a link to what looks like the patent for such a device. Perhaps even by the person Charles mentioned, as the patent shows the Inventor was from Cheyenne, WY. Granted in 1983 and I would guess it had a term of 20 years, but I am not a PTO expert. It's kind of interesting to see the old sketches/figures there... and wonder why this doesn't exist. :unamused:
I am quite sure that a servo, 2.4GHz radio, LEDs (for alignment), small capacity Li-Ion battery, and optical plummet (plus an Hm reference mark if Trimble were to build it) could be constructed to fit into a standard "puck" diameter housing less than 100mm tall that could be used to rotate a typical prism (62mm) horizontally. From what I comprehend, this type of setup would be inherently more accurate than any 360° prism (that exists today), provided the placement tolerance of the servo on the rotational axis was appropriately minimized. As for vertical tilt, that would likely have to come as a purpose built kit, but the cost-benefit ratio on that probably wouldn't be worth it.
I guess I will just keep dreaming.