%N pbextent %F $MIR/src/subs/pb.for
%D Return the extent of a primary beam.
%P rjs
%: image-data
%B
      subroutine pbExtent(pbObj,x,y,xext,yext)

      integer pbObj
      real x,y,xext,yext
  ---------------------------------------------------------------------
  Return information about a primary beam.

  Input:
    pbObj      Handle of the primary beam object.
  Output:
    x,y        The primary beam centre, in grid units.
    xext,yext  The distance to which the primary beam
               can be assumed to be non-zero.
    The primary beam will be non-zero only in the region
    [x0-xext,x0+xext] x [y0-yext,y0+yext].
