  The distance from a given position toward one or more destinations, exits,
and way points is a more or less important input variable in most models of
pedestrian dynamics. Except for the special case when there are no obstacles in
a concave scenario -- i.e. each position is visible from any other -- the
calculation of these distances is a non-trivial task. This isn't that big a
problem, as long as the model only demands the distances to be stored in a
Static Floor Field also called Potential Field, which never changes throughout
the whole simulation. In this case a pre-calculation once before the simulation
starts is sufficient. But if one wants to allow changes of the geometry during
a simulation run -- imagine doors or the blocking of a corridor due to some
hazard -- in the Distance Potential Field, calculation time matters strongly.
This contribution gives an overview over existing and new exact and approximate
methods to calculate a potential field, analytical investigations for their
exactness, and tests of their computation speed. The advantages and drawbacks
of the methods are discussed.
