Border style in MapServer

Question

I have WMS polygonal layer and want to draw polygon's border with the following style:

My symbol's description:

SYMBOL 
  NAME "double_line" 
  TYPE vector 
  POINTS 
    0 0 1 0 -99 -99 0 1 1 1
  END 
END

CLASS section in mapfile:

    CLASS
    STYLE
        OUTLINECOLOR 255 0 0
        SYMBOL 'double_line'
        SIZE 3
        WIDTH 1
    END

But in this case you can see self intersection in polygon's edge:

What is the righ way to get correct border style?

Answer 1

I've got solution from mapserver maillist:

STYLE
  OUTLINECOLOR 255 0 0
  GEOMTRANSFORM (BUFFER([SHAPE], -1))
END
STYLE
  OUTLINECOLOR 255 0 0
  GEOMTRANSFORM (BUFFER([SHAPE], 1))
END