find a bounded suboptimal solution which considers both
traveling time and sensing time with respect to a pre-defined
set of sensing positions. However, the problem of selecting
the initial set of sensing positions remains open and the
approach presents scalability issues when the cardinality of
the set is increased.
In the past decades, there has been extensive work on
problems which are closely related to the one addressed in
this paper. Ignoring the cost associated to sensing actions, our
problem could be reduced to the Generalized Covering Salesman Problem [8], whose instances are solved by generating
paths from which the whole environment can be observed.
A similar problem is solved in [9], where an approach based
on mixed integer linear programming is used for finding a
surveillance route for a mobile camera.
Neglecting the cost associated to the movements of the
robot, our problem could be reduced to an Art Gallery
Problem [10] or to a View Planning Problem [11]. The
art gallery problem is NP-hard in its most common variants and view planning is isomorphic to the Set Covering
Problem [12], a well known NP-complete problem. This
family of problems has been extensively studied over the
past decades [13], [14], but the algorithms proposed for
optimal solutions are effective under restricted assumptions,
such as not considering occlusions in the field of view of
the sensors [15], or work only when the number of possible
sensing positions is relatively small [16], [17]. There exist,
however, efficient algorithms for calculating approximated
solutions [18] for problem instances with a large number of
possible sensing positions. The solutions described above,
however, present two major drawbacks in our context: First,
they are mostly concerned with camera placement problems,
which means that they rarely consider limited field of view;
second, they do not consider the cost of moving from one
sensor position to the next. On the other hand, assuming
known sensing positions, we would still need to solve a
(Metric) Traveling Salesman Problem, that is, we should
find the shortest tour that connects all the sensing positions.
This is a well-known NP-hard problem, but it is possible to
optimally solve very large TSP instances, with thousands of
locations