Some readers have requested clarification about the assumptions on the
capabilities of searchlights. In particular, about whether boundary
searchlights can rotate past their adjacent walls. As stated in the
literature, a searchlight is a rotatable beam sensor which ``cannot
penetrate the environment boundary''. It is intended here that the
environment boundary only restricts a searchlight's ability to sense, not
its rotation. All searchlights, even those located on the environment
boundary, are free to rotate 360 degrees. A beam may thus have length zero
if its respective searchlight is aiming into a wall, but it is free to aim
there. This assumption on searchlight rotation capabilities is the most
natural because it means that there is no discontinuity in a searchlight's
rotation range as its location approaches and then goes onto the environment
boundary. There also are important computational implications of the
assumption, e.g., to guarantee a rotation monotone schedule exists as in
Conjecture 3.1 of the IJCGA paper **A Complete Algorithm for
Searchlight Scheduling** (Chapter 3, Conjecture 3.1 of the
dissertation **Visibility Problems for Sensor Networks and Unmanned Air
Vehicles**).

In the GNC paper **Sampling-Based Roadmap Methods for a Visual
Reconnaissance UAV** and Chapter 5.3 of the PhD dissertation
**Visibility Problems for Sensor Networks and Unmanned Air Vehicles**,
the convergence theorems require a general position assumption. We provide a
detailed description of the general position assumption in Section IV.A
of this
JGCD article.

Last modified: Sun Feb 5 23:07:27 MST 2012