On 1/17/07, <b class="gmail_sendername">Nicola Ranaldo</b> <<a href="mailto:ranaldo@unina.it">ranaldo@unina.it</a>> wrote:<div><span class="gmail_quote"></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
On Wednesday 17 January 2007 20:33, Nick Black wrote:<br>> I know that shapefiles store topology, but I dont know much about the<br>> details of it.<br>><br>> <a href="http://www.esri.com/news/arcuser/0401/topo.html">
http://www.esri.com/news/arcuser/0401/topo.html</a><br><br>Pleae check <a href="http://en.wikipedia.org/wiki/Shapefile#Topology_and_shapefiles">http://en.wikipedia.org/wiki/Shapefile#Topology_and_shapefiles</a>,<br>it seems some formats does not support topology.
<br><br>[...]<br>> I'm loathed to start another format war, but OSM's model has a lot<br>> going for it - and has considerably more documentation than Mapinfo's<br>> format!<br><br>You are right, howewer we lack:
<br><br>1) hierarchycal ways<br>2) advanced support for areas<br><br>As the first may be a long term goal, the second is necessary to elevate osm<br>to a full featured model. Actually we cannot define areas with inner holes
<br>while the other formats do.</blockquote><div><br>I think maybe you can. Because ways can be non-contiguous, you can create an area that comprises an outer circle and an inner circle. If the outer circle is clockwise and then inner anti-clockwise then using something like the SVG non-zero rule, you get a definition of areas with holes.
<br><br>If you use the SVG even-odd rule, which is the other way of doing it, then you don't even need to ensure that the inner circle is anti-clockwise.<br><br>The osmarender rule files currently implement the non-zero rule. See:
<a href="http://dev.openstreetmap.org/~ojw/Tiles/tile.php/16/32674/21824.png">http://dev.openstreetmap.org/~ojw/Tiles/tile.php/16/32674/21824.png</a> for an example of some lakes containing islands.<br><br>80n<br><br><br>
</div><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Niko<br><br><br>_______________________________________________<br>dev mailing list
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