MS RFC 49: Symbology, Labeling, and Cartography Improvements

Date:2009/01/26
Authors:Thomas Bonfort, Stephen Lime
Contact:Thomas.Bonfort at camptocamp.com , Steve.Lime at DNR.State.MN.US
Status:Passed and Implemented
Version:MapServer 5.4

Purpose

This RFC regroups a few minor additions or changes to the MapServer rendering or mapfile syntax.

These changes are/were all in RFC45, but were extracted to keep things moving on as some of the stuff in RFC45 lacks funding in the near future.

Fractional values for SIZE and WIDTH

AGG can deal with fractional widths and sizes but styleObj’s define those properties as int’s. Shouldn’t be a big deal since both GD and AGG don’t use those values directly, rather they use scaled values with are cast or rounded to an int if necessary.

https://github.com/mapserver/mapserver/issues/2766

MINSCALEDENOM / MAXSCALEDENOM for STYLEs and LABELS

These keywords can reduce mapfile size and maintenance, by avoiding creating multiple layers or classes.

https://github.com/mapserver/mapserver/issues/2865

OUTLINEWIDTH on line layers

It is currently impossible to draw a outlined line with a scale-dependant width. We propose to add the OUTLINWIDTH keyword to the STYLE block, that indicates the width in pixels that should be rendered around the main line color.

The implementation of this lies in mapdraw.c. When a line’s style block has an outlinewidth, the underlying shape is actually drawn twice: once with it’s width adapted to account for the outlinewidth, and once normally. The current caching mechanism for lines is preserved.

example usage:

LAYER
  TYPE LINE
  SIZEUNITS meters
  CLASS
    STYLE
      COLOR 255 0 0
      OUTLINECOLOR 0 0 0
      OUTLINEWIDTH 1
      WIDTH 25 #this is in meters (ground units)
      MINWIDTH 1 #minimal width (in pixels) for far zoomed maps
      MAXWIDTH 20 #maximal width (in pixels) for close zoomed maps
    END
  END
END

whatever the map extent or scale, this line layer would always be rendered by a red line with a one pixel black outline.

https://github.com/mapserver/mapserver/issues/2865

add LABEL to layersObj

Note

This feature has not yet been implemented

so that a default can be defined for all classes (sort of like templates). A class label would take precedent.

https://github.com/mapserver/mapserver/issues/XXX

Affected Files

  • mapfile.c
  • mapdraw.c (outlinewidth on lines, scale on styleobj)
  • mapserver.h
  • maplabel.c (scale on labels)

Documentation

The documentation for the keywords will be aded to the main mapfile syntax docs.

Mapscript

Getters and Setters for the keywords will be added for mapscript availability

Backwards Incompatibility

None Expected

Comments from Review period

  • the LABELMETHOD proposal is withdrawn

  • fractional values also for pattern,gap, offset: a good candidate for 6.0 (when pattern and gap would be moved to the styleObj?)

  • there was consensus for adding parametered scaling, useful for thematic mapping (eg size proportional to a feature attribute)

    • by allowing simple expressions, eg SIZE ( 18 + [poptotal] * (( 43-18)/(5000-30000)) )

    • or by adding pseudoitems at the layer level:

      PSEUDOITEM
       'mySize' (mrange([itemname], mininput, maxinput, minoutput,
      maxoutput))
       'myText (commify(round([itemname], 2)) + ' ac')
      END
      
      LABELITEM 'myText'
      CLASS
       STYLE
        COLOR 255 0 0
        SIZE [mySize]
       END
       LABEL
        ...
       END
      END
      

    this enhancement will be addressed in a specific rfc.

Voting History

+1 : SteveW, UmbertoN, TamasS, SteveL, DanielM (,AlanB)