[mapserver-users] Displaying overlapping linestrings

[Jan Hartmann]

Yes, the idea works, but the differences in hue are too small to be 
useful in practice. And furthermore, they also show up for border lines 
between adjoining polygons. I just want to highlight polygons that 
completely overlap. I'm afraid I have to go the PostGIS/GEOS way.

Even o, would an XOR brush not be a nice addition to the STYLE object? 
You could create all kinds of moiré fill patterns.

http://www.google.nl/search?q=moire&hl=en&client=firefox-a&hs=lGh&tbo=u&rls=org.mozilla:en-GB:official&tbm=isch&source=univ&sa=X&ei=C1UCUez4C9KX0QXV9IDoDw&ved=0CFMQsAQ&biw=1600&bih=809

Jan

On 1/24/2013 6:36 PM, Lime, Steve D (DNR) wrote:
>
> You could try drawing the features with the same base color but with 
> opacity set. The more times the same area is rendered you'd get a 
> different hue.
>
> Steve
>
> *From:*mapserver-users-bounces at lists.osgeo.org 
> [mailto:mapserver-users-bounces at lists.osgeo.org] *On Behalf Of *Jan 
> Hartmann
> *Sent:* Thursday, January 24, 2013 11:00 AM
> *To:* Stephen Woodbridge
> *Cc:* mapserver-users at lists.osgeo.org
> *Subject:* Re: [mapserver-users] Displaying overlapping linestrings
>
> On 01/24/2013 05:35 PM, Stephen Woodbridge wrote:
>
>     On 1/24/2013 11:13 AM, Jan Hartmann wrote:
>
>     Does anyone know a trick to do this:
>
>     I'm making geographical indexes for the map series in our map
>     library.
>     Each map sheets is displayed as a polygonal linestring, based on its
>     corner coordinates. Lots of sheets have exactly the same
>     boundaries, so
>     it's not clear where a polygon indicates just one map sheet of
>     several.
>     It's easy, of course, to write a PostGIS query to return a different
>     color code when map boundaries exactly coincide, but I was wondering
>     whether something like that could be done by mapserver on its own,
>     like
>     XOR-ing a line with what is already there. Any ideas?
>
>
>     Hi Jan,
>
>     For polygons you could use a small negative buffer to shrink the
>     polygon slightly. You can do this in postgis, and you might be
>     able to do it with mapserver if geos is compiled in. See:
>
>     http://mapserver.org/development/rfc/ms-rfc-48.html
>
> No, that is not what I meant. I'm looking for a trick for mapserver to 
> color a linestring differently when drawing over a linestring that it 
> has already drawn in a previous layer. In computer graphics you can do 
> this by using an XOR brush. Essentially, the screen frame buffer 
> functions as a sort of memory. I don not want to use PostGIS or GOS, 
> too complex. I doubt if this can be done by MapServer, but you never know.
>
> Jan
>
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