# File easy_vtk.rb, line 365
  def plane( origin, normal, options={} )
    opacity = false
    axes = false
    options.each{ |key, val|
      case key
      when 'opacity'
        opacity = val
      when 'axes'
        axes = val
      else
        raise "option (#{key}) is invalid"
      end
    }
    plane = Vtk::Plane.new
    plane.SetOrigin( origin )
    plane.SetNormal( normal )
    cutter = Vtk::Cutter.new
    cutter.SetInput( @grid )
    cutter.SetCutFunction( plane )
    mapper = Vtk::PolyDataMapper.new
    mapper.SetInput( cutter.GetOutput )
    if @lookupTable
      mapper.SetLookupTable( @lookupTable )
    else
      @lookupTable = mapper.GetLookupTable
    end
    actor = Vtk::Actor.new
    actor.SetMapper( mapper )
    actor.GetProperty.SetOpacity( options['opacity'] ) if opacity
    @ren.AddActor( actor )
    draw_axes( cutter, axes ) if axes
    return nil
  end