[mapserver-users] Displaying overlapping linestrings

[Jan Hartmann]

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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