[mapserver-users] Displaying overlapping linestrings

[Lime, Steve D (DNR)]

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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