PLANE_OLD

        PLANE_OLD

    This is a (very) simple task that subtracts a plane from an  image.  The
    plane  is  determined  by  three  non-colinear non-blanked pixels of the
    original map.  The plane image is also computed.  This task is usually a
    first   step  before  more  elaborate  background  algorithms  (such  as
    BACKGROUND or MAKE_BACK) are applied.