PLANE

        PLANE

    This is a simple task that subtracts a plane from an  image.  The  plane
    is determined by least square fitting through all non-blanked pixels  of
    the  original map, weighted by a weight image. The latter can be used to
    account for a non uniform signal to noise ratio, but is more  frequently
    used to ignore some areas (typically the sources) in the fit.

    It  supersedes  an older obsolete version (still available as PLANE_OLD)
    which fitted a plane through 3 points of the input image.