Objects of class ltraj
are often created with data collected
using some form of telemetry (radio-tracking, G.P.S., etc.). However,
the relocations of the monitored animals are always somewhat
imprecise. The function mindistkeep considers that when
the distance between two successive relocations is lower than a given
threshold distance, the animal actually does not move (and replaces
the coordinates of relocation i+1 by the coordinates of relocation
i).