[OSM-dev] Playing with MapServer WMS and WFS

Emilie Laffray emilie.laffray at gmail.com
Mon Sep 13 16:16:22 BST 2010

On 13 September 2010 15:53, Peter Körner <osm-lists at mazdermind.de> wrote:

> Am 11.09.2010 08:26, schrieb Jukka Rahkonen:
>  Pretty easy and in theory it works immediately after osm2pgsql import
>> without any other preprocessing. However, I did not put it into mapfile
>> because rendering fails after ST_PointOnSurface failing first with some
>> polygons:
>> NOTICE:  TopologyException: found non-noded intersection between
>> LINESTRING (8569.5 4234.62, 8623.96 4373.11) and LINESTRING (8637.48
>> 4400.77, 8610.45 4345.45)at 8623.96 4373.1
> Yes, that's a known problem (or feature?). OSM allows invalid geometries
> for polygons and mapnik can render them, but some postgis functions will
> fail. It is possible to use ST_IsValid but this adds a medium runtime
> penalty.
> To come around this we could add an isvalid coumn to the polygon table.
> This column can be filled via a trigger or via osm2pgsql. This would move
> the penalty to the import.

There are two ways of dealing with invalid geometries.
I have used in the past either ConvexHull or buffer to make them valid for
analysis purpose. That's what I did for the Corine Import for France.

Emilie Laffray
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