[Geotools-gt2-users] Controlling Anti-Aliasing in Shape File Rendering

[Gary L. <gw...@so...>]

A co-worker of mine had a question regarding anti-aliasing settings and =
SLD files. I took a look through the GeoTools code base and haven=E2=80=
=99t been able to answer him, and I was wondering if anyone here could p=
oint me in the right direction.

My co-worker is using an Ajax-based web browser application that request=
s transparent GIF files using a WMS request to GeoServer. He uses these =
GIF=E2=80=99s to create a sandwich of overlays, allowing the user to swi=
tch between different combinations of images depending on what he wants =
to see (some of the images are produced by data systems that are outside=
 scope of the GeoServer implementation).
=20
Everything works fine except that the line and text graphics produced by=
 GeoServer are rendered with anti-aliasing. Now typically, when a graphi=
cs environment draws a black line on a white background with anti-aliasi=
ng, it will attempt to soften that saw-tooth effect that is sometimes vi=
sible on angled lines by setting the color of pixels on or adjacent to t=
he line to some intermediate color tone. Thus when my co-worker requests=
 an overlay of geopolitical outlines drawn in a rather dark color and th=
e anti-aliasing in GeoServer assumes a white background, the transparent=
 GIF comes back with dark lines speckled with light gray dots. Of course=
, he could just change the background, but even as a band-aid fix that d=
oesn=E2=80=99t really work because sometimes he needs to sandwich images=
 on light background and sometimes he uses dark. If we adjust the SLD fi=
les for light-colored lines on a dark background, we get a corresponding=
 unsightly effect.

So the question: What=E2=80=99s the best way to suppress the anti-aliasi=
ng effects=3F A couple of obvious ideas suggest themselves immediately, =
but looking through the GeoTools code I don=E2=80=99t see any place wher=
e they might be implemented (I haven=E2=80=99t looked through the GeoSer=
ver code because I am still struggling to learn GeoTools, and don=E2=80=
=99t think I could handle another challenge right now). I know that an a=
pplication can suppress aliasing by using the java.awt.RenderingHints cl=
ass, but I=E2=80=99m not sure how to get the proper values passed into G=
eoTools. I thought that there might be a specification in the SLD format=
 to turn off aliasing, but I don=E2=80=99t see it in the OpenGIS documen=
ts I=E2=80=99ve searched. An alternative approach might be to hack the G=
eoServer code so that when a WMS request comes in for a transparent GIF,=
 it just turns off anti-aliasing=E2=80=A6 except that, first, I don=E2=
=80=99t believe in doing that kind of non-standard stuff if it can be av=
oided and, second, I don=E2=80=99t know where to begin to make the chang=
e even if I concluded that was the only way to get the job done.

Anyway, I apologize in advance if there=E2=80=99s an easy way of doing t=
his and I=E2=80=99ve missed something obvious in the documentation. Than=
ks for your help.

Gary


P.S. My co-worker has produced some sample images that do an admirable j=
ob showing the anti-aliasing effect. If anyone is unfamiliar with the ef=
fect and would like to see what it does, please let me know and I will s=
end copies of the images.


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Computer Science is the Art of the Possible
Gary W. Lucas, Senior Software Engineer
Sonalysts, Inc
215 Parkway North
Waterford, CT 06320
(860) 326-3682