function changegrid, newgrid
;
;
  compile_opt idl2, strictarrsubs
;
@cm_4mesh
;
;
   if cmpgrid(newgrid) EQ 0 then return, 0
;
; update the common paramaters
;
   ccmeshparameters = newgrid

   ixminmesh = newgrid.ixminmesh
   ixmaxmesh = newgrid.ixmaxmesh
   iyminmesh = newgrid.iyminmesh
   iymaxmesh = newgrid.iymaxmesh
   izminmesh = newgrid.izminmesh
   izmaxmesh = newgrid.izmaxmesh
;
; read the new file
;
   loadgrid, newgrid.filename
;
  IF NOT keyword_set(key_forgetold) THEN BEGIN
   @updateold
  ENDIF
;
   return, 1
end