[mapserver-dev] Labeling Highway Shields Idea

[Stephen Woodbridge]

Hi all,

Currently, unless I'm out of date, if you want to place highway shields 
that are symbols as part of a label you have to use an annotation layer 
to place the shield as a symbol(s) and the label over top of that with 
the number.

So this requires, two passes over the data, one to render the highways 
and a second pass over the data to place the shields. It also requires 
defining and maintaining two layers in place of one.

A proposal for an alternate way:

One way to do this would be to allow STYLE block(s) to be placed in the 
LABEL block and these would use the base label point and be rendered 
before the label text and only if the label test is rendered. I say base 
label point, because you would still want to be able to use OFFSET x y 
to align the label text with the shield symbols. I suppose you could 
allow OFFSET x y in the STYLE block to allow separate positioning of the 
symbols and to get multiple symbols to align correctly with one another.

The following is an example of how this might look. Sorry, I copied it 
from the cpp input file but it should be easy to understand. 
_label(font,size,color) is a macro simplify the files. If USE_SHIELDS is 
defined it would use the proposal above and render the interstate 
shields which is actually three symbols representing the red, white and 
blue parts of the shield where each is a vector symbol or you could have 
one STYLE block that uses an image symbol for the shield. If USE_SHIELDS 
is not defined then you would get a OSM style highway label in a box, 
like "[I-290]".

Thoughts on this?

If people think this would be a good enhancement, I would be happy to 
write up a ticket for it.

Thanks,
   -Steve

     CLASS ## Interstate
       EXPRESSION "1"
       STYLE
         WIDTH _motorway_width
         OUTLINEWIDTH 1
         OUTLINECOLOR _motorway_ol_clr
         MINWIDTH _motorway_minwidth
         MAXWIDTH _motorway_maxwidth
       END
       STYLE
         WIDTH _motorway_width
         COLOR _motorway_clr
         MINWIDTH _motorway_minwidth
         MAXWIDTH _motorway_maxwidth
       END
#ifdef USE_SHIELDS
       LABEL
         MAXSCALEDENOM 3000000
         STYLE
           SYMBOL "interstate-red"
           COLOR _red_clr
         END
         STYLE
           SYMBOL "interstate-blue"
           COLOR _blue_clr
         END
         STYLE
           SYMBOL "interstate-white"
           COLOR _white_clr
         END
         _label("arial-bold",10,_white_clr)
         PRIORITY 1
         MINSIZE 8
         MAXSIZE 8
         MINDISTANCE 150
       END
#else
       LABEL
         MAXSCALEDENOM 3000000
         _label("arial-bold",10,_white_clr)
         PRIORITY 1
         MINSIZE 8
         MAXSIZE 8
         MINDISTANCE 150
         MAXLENGTH 6
         BACKGROUNDCOLOR _motorway_lbl_bg_clr
         BACKGROUNDSHADOWCOLOR _motorway_lbl_shadow_clr
       END
#endif
     END