Displaying a symbol label using an expression in MapServer 7

Question

I want to label the numbered roads at all scales with a symbol instead of text. Also, I would like to label the roads using an expression so I could use the symbol corresponding to the road number.

Right now, I can display a symbol in a label, but the text is still visible and all roads use the same symbol. I can't find a way to use expressions in a LABEL.

So how could I dynamically use a symbol as label, without text, according to a field attribute that stores the road number?

Here is how a part of my LAYER section looks like:

LABELITEM "NomRte"
CLASS
  NAME 'Autoroute'
  EXPRESSION (('[ClsRte]' eq 'Autoroute')and('[CaractRte]' ne 'Bretelle'))

  LABEL
    MINDISTANCE 750
    STYLE    # since to version 6
      symbol 'a10'
      MAXSIZE 24.0
    END # STYLE
  END # end of label

  STYLE
    WIDTH 2
    COLOR 0 0 0
    OUTLINECOLOR 0 0 0
    MAXSCALEDENOM 500000
  END #STYLE

Answer 1

I got that working. It is pretty simple, but I got confused in MapServer's documentation. My mapfile (layer level) now looks like this

LAYER

[...]

CLASS
  NAME 'Route régionale'
  EXPRESSION (('[ClsRte]' eq 'Régionale')and('[CaractRte]' ne 'Bretelle'))

  LABEL
    EXPRESSION ([NoRte] = 141)
    TEXT ' '
    MINDISTANCE 150
    STYLE    # since to version 6
      symbol 'r141'
      MAXSIZE 20.0
    END # STYLE
  END #LABEL


  LABEL
    EXPRESSION ([NoRte] = 243)
    TEXT ' '
    MINDISTANCE 300
    STYLE    # since to version 6
      symbol 'r243'
      MAXSIZE 20.0
    END # STYLE
  END #LABEL

  LABEL
    EXPRESSION ([NoRte] = 245)
    TEXT ' '
    MINDISTANCE 175
    STYLE    # since to version 6
      symbol 'r245'
      MAXSIZE 20.0
    END # STYLE
  END #LABEL
END #CLASS

[...]



END #LAYER