AntiAliasing with MapServer¶
- Author:
Pericles Nacionales
- Contact:
naci0002 at umn.edu
- Last Updated:
2009/01/17
Avvertimento
This document is outdated.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
Nota
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.
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
Add TRANSPARENCY to the LAYER object and set value to ALPHA
MAP
...
IMAGETYPE PNG24
...
LAYER
...
TRANSPARENCY ALPHA
...
END
END
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
Nota
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:
Nota
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.
1MAP
2 NAME 'ms101'
3 EXTENT -2198022.00 -2444920.25 2707932.00 1234545.25 # CONUS LAEA (US)
4 SIZE 640 480
5 SHAPEPATH 'data'
6 SYMBOLSET 'symbols/symbols.txt'
7
8 IMAGETYPE PNG24
9
10 PROJECTION
11 "init=epsg:2163"
12 END
13
14 # The layer below will be rendered as 1-pixel wide, antialiased line
15 # If you'd like to change the line thickness add the WIDTH keyword
16 # in the STYLE object with a value of 3 or greater.
17 LAYER # begin antialiased country boundary (line) layer
18 NAME 'country_line'
19 DATA 'shapefile/WorldCountryBorders.shp'
20 TYPE LINE
21 STATUS ON
22 TRANSPARENCY ALPHA
23
24 PROJECTION
25 "init=epsg:4326"
26 END
27
28 CLASS
29 NAME 'Country Boundary'
30 STYLE
31 COLOR 96 96 96
32 ANTIALIAS TRUE
33 END
34 END
35 END # end country boundary layer
36
37 # The layer below shows one way to draw a polygon with antialiased outline
38 LAYER # begin antialiased country boundary (polygon) layer
39 NAME 'country_line'
40 DATA 'shapefile/Countries_area.shp'
41 TYPE POLYGON
42 STATUS ON
43 TRANSPARENCY ALPHA
44
45 PROJECTION
46 "init=epsg:4326"
47 END
48
49 CLASS
50 NAME 'Country Boundary'
51 STYLE
52 COLOR 212 212 212
53 OUTLINECOLOR 96 96 96
54 WIDTH 3
55 ANTIALIAS TRUE
56 END
57 END
58 END # end country boundary polygon layer
59
60 # The layer below shows one way to draw a polygon with antialiased outline
61 LAYER # begin antialiased state boundary (line) layer
62 NAME 'state_line'
63 DATA 'shapefile/us_states.shp'
64 TYPE LINE
65 STATUS ON
66 TRANSPARENCY ALPHA
67
68 PROJECTION
69 "init=epsg:4326"
70 END
71
72 CLASS
73 NAME 'State Boundary'
74 STYLE
75 COLOR 144 144 144
76 SYMBOL 'cartoline'
77 ANTIALIAS TRUE
78 END
79 END
80 END # end state line layer
81END # end of map file
Here’s how the “cartoline” symbol is defined:
Nota
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
Nota
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.