Question

I’m using mapnik 0.7.1 and tilelite with openlayers. I would like to prescribe two rules under a style for a shapefile layer (within layers-shapefiles.xml.inc), however, liteserv.py will not start if I do this. I also tried two styles for this layer (one rule per style), but same result. Here is the style block:

<Style name="wilderness_boundaries">
    <Rule>
      &maxscale_zoom0;
      &minscale_zoom9;
      <PolygonSymbolizer>
        <CssParameter name="fill">#72B656</CssParameter>
      </PolygonSymbolizer>
      <LineSymbolizer>
        <CssParameter name="stroke">grey</CssParameter>
        <CssParameter name="stroke-width">1.0</CssParameter>
        <CssParameter name="stroke-dasharray">4,2</CssParameter>
      </LineSymbolizer>
    </Rule>

    <Rule>
      &maxscale_zoom10;
      &minscale_zoom20; 
      <PolygonSymbolizer>
        <CssParameter name="fill">#72B656</CssParameter>
      </PolygonSymbolizer>
      <LineSymbolizer>
        <CssParameter name="stroke">grey</CssParameter>
        <CssParameter name="stroke-width">1.0</CssParameter>
        <CssParameter name="stroke-dasharray">4,2</CssParameter>
      </LineSymbolizer>
      <TextSymbolizer name="NAME" fontset_name="book-fonts" size="8" dy="2" fill="grey" halo_radius="1" />
    </Rule>

</Style>

and the corresponding layer definition:

<Layer name="wilderness_boundaries" status="on" srs="&srs4326;">
    <StyleName>wilderness_boundaries</StyleName>
    <Datasource>
      <Parameter name="type">shape</Parameter>
      <Parameter name="file">&world_boundaries;/wilderness_EPSG4326.shp</Parameter>
      <Parameter name="encoding">latin1</Parameter>
    </Datasource>
</Layer>

If I execute generate_image.py with this configuration, I get a segmentation fault.

As you can see, I am trying to show wilderness area polygons at all zoom levels, but label them only at zoom levels above 10. Multiple rules are allowed for a given style in osm.xml, what am I missing?

Thanks,
John

Answer 1

a segfault indicates you forgot to run generate_xml.py – in other words the styles sheet still has files in the inc/ directory that have %(something)s that need filled in. libxml2, the library mapnik uses under the hood, has a silly bug that causes segfaults when entities cannot be loaded.