SYNOPSIS:
    FIELD_HATOP name radius height [maxerg]

DESCRIPTION:
    Use a "hat operator" on the given field. That is, find local
    minima or maxima. A point is considered to be one, if
    its neighbours that are no more then radius away fall below
    or rise at least by height.
    Results are limited by "maxerg", if given, only giving the
    results with the highest or lowest peak value.

