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# AntiAliasing with MapServer

Author

  Pericles Nacionales

Contact

  naci0002 at umn.edu

Last Updated

  2009/01/17

Warning

This document is outdated. Since version 6.0, MapServer will produce aliased output for the “gd/” drivers, and antialiased output for the “agg/” and “cairo/” ones

Note

For quality antialiased output from mapserver, it is highly recommended to use the AGG rendering. This document applies only if you wish to stick to the GD rendering, or if you are using a version predating the 5.0 release of mapserver.

Table of Contents

- AntiAliasing with MapServer

  - What needs to be done

## What needs to be done

1. Change (or add) IMAGETYPE keyword in MAP object to PNG24 (24-bit PNG output) or JPEG

    MAP
      ...
      IMAGETYPE PNG24
      ...
    END

2. Add TRANSPARENCY to the LAYER object and set value to ALPHA

    MAP
      ...
      IMAGETYPE PNG24
      ...

      LAYER
        ...
        TRANSPARENCY ALPHA
        ...
      END
    END

3. Add ANTIALIAS keyword to the STYLE object within the CLASS object within the LAYER and set value to TRUE

    MAP
      ...
      IMAGETYPE PNG24
      ...

      LAYER
        ...
        TRANSPARENCY ALPHA
        ...
        CLASS
          ...
          STYLE
            ...
            ANTIALIAS TRUE
            ...
          END
          \.\.\.
        END # end class
      END # end layer
    END # end map

Note

Don’t use the SYMBOL or the SIZE keywords within the CLASS object, instead use WIDTH to specify width of line or polygon outline. Don’t use WIDTH unless you have to. If you must define a SYMBOL, use symbol of type ELLIPSE–it supports antialiasing.

Here’s an example of a real-world mapfile:

Note

From MapServer 6, symbol type CARTOLINE is no longer supported. You have to use AGG rendering and STYLE PATTERN to achieve dashed lines. Therefore, the following example does not work anymore.

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    MAP
      NAME 'ms101'
      EXTENT -2198022.00 -2444920.25 2707932.00 1234545.25  # CONUS LAEA (US)
      SIZE 640 480
      SHAPEPATH 'data'
      SYMBOLSET 'symbols/symbols.txt'

      IMAGETYPE PNG24

      PROJECTION
        "init=epsg:2163"
      END

      # The layer below will be rendered as 1-pixel wide, antialiased line
      # If you'd like to change the line thickness add the WIDTH keyword
      # in the STYLE object with a value of 3 or greater.
      LAYER # begin antialiased country boundary (line) layer
        NAME 'country_line'
        DATA 'shapefile/WorldCountryBorders'
        TYPE LINE
        STATUS ON
        TRANSPARENCY ALPHA

        PROJECTION
          "init=epsg:4326"
        END

        CLASS
          NAME 'Country Boundary'
          STYLE
            COLOR 96 96 96
            ANTIALIAS TRUE
          END
        END
      END # end country boundary layer

      # The layer below shows one way to draw a polygon with antialiased outline
      LAYER # begin antialiased country boundary (polygon) layer
        NAME 'country_line'
        DATA 'shapefile/Countries_area'
        TYPE POLYGON
        STATUS ON
        TRANSPARENCY ALPHA

        PROJECTION
          "init=epsg:4326"
        END

        CLASS
          NAME 'Country Boundary'
          STYLE
            COLOR 212 212 212
            OUTLINECOLOR 96 96 96
            WIDTH 3
            ANTIALIAS TRUE
          END
        END
      END # end country boundary polygon layer

      # The layer below shows one way to draw a polygon with antialiased outline
      LAYER # begin antialiased state boundary (line) layer
        NAME 'state_line'
        DATA 'shapefile/us_states'
        TYPE LINE
        STATUS ON
        TRANSPARENCY ALPHA

        PROJECTION
          "init=epsg:4326"
        END

        CLASS
          NAME 'State Boundary'
          STYLE
            COLOR 144 144 144
            SYMBOL 'cartoline'
            ANTIALIAS TRUE
          END
        END
      END # end state line layer
    END # end of map file

Here’s how the ‘cartoline’ symbol is defined:

Note

From MapServer 6, symbol type CARTOLINE is not available. You have to use AGG rendering and STYLE PATTERN to achieve dashed lines. Therefore, the following symbol can not be used anymore.

    SYMBOL
      NAME 'cartoline'
      TYPE CARTOLINE
      LINECAP "round"
      LINEJOIN "round"
      LINEJOINMAXSIZE 3
    END

Note

The examples provided here are for illustrative purposes only–keep your map file definitions simple. Antialiasing adds computing overhead on the server and could slow/degrade its performance. Don’t use it unless you must and certainly don’t use symbols with it unless you really have to.