[mapserver-users] polygon border artifacts

[Lime, Steve D (DNR)]

The artifacts are more or less prominent depending on the color something is drawn over. I think it's a result
of the analytic anti-aliasing done by AGG. I had read a thread once that talked about it, I recall it being most
prominent with horizontal and vertical lines. In the example Sven provided if you change the IMAGE color also to
blue you don't see any artifacts between ocean polys, although of course you don't see the islands, so the artifacts
is related to anti-aliasing blue on red. A different background might make it more subtle.

The work around is easy enough, draw an outline, although I don't know why anti-aliasing associated with that rendering
doesn't itself produce an artifact.

Steve

-----Original Message-----
From: Rahkonen Jukka [mailto:Jukka.Rahkonen at mmmtike.fi] 
Sent: Monday, May 07, 2012 1:05 PM
To: Lime, Steve D (DNR); Sven Geggus; mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] polygon border artifacts

Hi,

Perhaps it is mostly an AGG issue because I think that Mapnik makes similar artifacts too.  See Corine landuse polygons here  http://www.openstreetmap.org/?lat=60.820709&lon=27.201925&zoom=18&layers=M
Sea areas do not have artifacts in OSM because sea is just background colour and is is not rendered at all from any data. But I do not know what Mapnik is doing with the land polygons. I cannot see artifacts between them in OMS maps.

-Jukka Rahkonen-

Lime, Steve D wrote:

> I tried locally and it's definitely a rendering artifact related to anti-aliasing. Should an outline always be drawn?


> -----Original Message-----
> From: mapserver-users-bounces at lists.osgeo.org 
> [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf > Of Sven 
> Geggus
> Sent: Friday, May 04, 2012 6:04 AM
> To: mapserver-users at lists.osgeo.org
Subject: Re: [mapserver-users] polygon border artifacts

thomas bonfort <thomas.bonfort at gmail.com> wrote:

> with a recentish version of mapserver, try setting PROCESSING 
> "APPROXIMATION_SCALE=FULL"
> on your ocean layer, to avoid feature simplification (it will slow 
> down the rendering if the resolution of your data is much greater than 
> the resolution of the requested map).

Hm. Looking at the sources 6.0.1 seems to be recent enough, but unfortunately this does not seem to fix the problem.

Regards

Sven

--
Den Rechtsstaat macht aus, dass Unschuldige wieder frei kommen (Wolfgang Schäuble)

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