[mapserver-users] Rendering of adjacent dashed lines

[Rahkonen Jukka (MML)]

Hi,

Trying to guess the answer myself. Generally it may not give good results at all to render features and styles one by one:

feature 1 - style 1
feature 1 - style 2
feature 2 - style 1
feature 2 - style 2

The result could look something like the “Unexpected results” in http://www.mapgears.com/en/blog/archive/2013-03-05-roads_network_mapping
Usually the result will look better if style 1 for all the features is rendered at the bottom and style 2 above that. It may be that http://mapserver.org/development/rfc/ms-rfc-54.html is somehow related.

A side effect is that the “dashed line with solid white background” trick which seems to be well known in the internet does not work with Mapserver.

-Jukka-

Rahkonen Jukka wrote:

Hi,

I would like to know why it does not work by painting solid white line underneath and dashed line above it.  If the totally overlapping lines were painted one by one, the last line would cover the dashes of the previously rendered line with total white and the result would look like it does in QGIS and ArcCAD.  Mapserver must do it in somehow different way so that the white line of the last linestring does not paint over everything that has been rendered before.

-Jukka Rahkonen-

Richard Greenwood wrote:

As others have suggested, you need to "preprocess your data to merge adjacent lines into one". This can be done with topology. PostGIS has topology support. You would have to convert (and maintain) your simple features polygons as a PostGIS topology and then render them as lines (not polygons) in MapServer. There is also TopoJSON but I have not used it. I think it provides client-side support for topology, which is not exactly what you are asking about, but might be worth a look.

Rich


On Fri, Jun 17, 2016 at 2:47 PM, Ziegler Stefan <Stefan.Ziegler at bd.so.ch<mailto:Stefan.Ziegler at bd.so.ch>> wrote:
Hi Jukka

Yes. Seems similar to what you can do with QGIS.

Regards
Stefan

> -----Ursprüngliche Nachricht-----
> Von: Rahkonen Jukka (MML) [mailto:jukka.rahkonen at maanmittauslaitos.fi<mailto:jukka.rahkonen at maanmittauslaitos.fi>]
> Gesendet: Freitag, 17. Juni 2016 16:20
> An: Ziegler Stefan; 'mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>'
> Betreff: Re: Rendering of adjacent dashed lines
>
> Hi,
>
> The only method that really works is to remove adjacent lines. Your trick seems to be
> the same as this https://knowledge.autodesk.com/support/autocad-map-
> 3d/troubleshooting/caas/sfdcarticles/sfdcarticles/Using-a-dashed-line-symbol-with-
> adjacent-polygons-masking.html
> but they used a wider white line. However, it feels usable only if the background is also
> white and there are no lines very close to each other.
>
> -Jukka Rahkonen-
>
>
> Ziegler Stefan wrote:
>
> > Hi
>
> > I'm trying to render some lines with a pattern. This works and looks great as long as
> the lines are not adjacent. When the lines share a common border the dashed lines
> may look ugly since one dashed line is rendered on top of the other rendered dashed
> line. I tried to add a white solid line under the dashed line:
>
>     CLASS
>       STYLE
>         COLOR 255 255 255
>         WIDTH 2
>         LINECAP BUTT
>       END
>       STYLE
>         COLOR 0 0 0
>         WIDTH 2
>         LINECAP BUTT
>         PATTERN 20 4 2 4 2 4 END
>       END
>     END
>
>
> But the behaviour is still the same. Is there a trick/workaround for this? I'm using
> MapServer 7.0.1.
>
> Best regards
> Stefan Ziegler
>
>
>
> Freundliche Grüsse
> Stefan Ziegler
> Kantonsgeometer / Leiter Amt für Geoinformation
>
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>
> Telefon +41 32 627 75 96
> Telefax +41 32 627 75 98
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>
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--
Richard W. Greenwood, PLS
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