[OSM-talk] Mapnik now not supporting layer=1 on golfcourses

[Andy Robinson]

Jon Burgess [mailto:jburgess777 at googlemail.com] wrote:
>Sent: 14 May 2007 8:31 PM
>To: Andy Robinson
>Cc: talk at openstreetmap.org
>Subject: Re: [OSM-talk] Mapnik now not supporting layer=1 on golfcourses
>
>On Mon, 2007-05-14 at 19:26 +0100, Jon Burgess wrote:
>> On Mon, 2007-05-14 at 17:24 +0100, Andy Robinson wrote:
>> > We appear to have lost some golf course support in Mapnik in the most
>> > recent tiles rendered. Previously (as per osmarender still) golf
>> > course areas within parkland where the course has a layer=1 set were
>> > rendered one on top of the other for all to see, the current Mapnik
>> > tiles are no longer showing these golf courses. Example being:
>> >
>> >
>> >
>> > http://www.openstreetmap.org/index.html?lat=52.5740&lon=-1.8576&zoom=13
>> >
>>
>> It seems that the current code only uses the layer= property to
>> determine the drawing order (z_order) on lines and not on polygon areas
>> like the golf course & park.
>>
>> This is the case both for the old setup_z_order.sql script and the
>> current osm2pgsql. If it rendered OK before in Mapnik then it was
>> probably by luck.
>>
>> Adding this feature needs changes to both define a z_order for polygons
>> and also to use this to sort the data in the osm.xml style.
>>
>> 	Jon
>>
>
>I have just implemented the necessary changes to osm2pgsql and osm.xml
>to add a z_order for polygons. I have updated the render database to set
>the z_order values on the polygon table and use this new osm.xml file.
>
>The 4 tiles which make up the park at level 13 have been re-rendered and
>the golf course now shows up on the link above.
>
>I there there may be an outstanding issue with the layer= support
>however. I think the mapnik code rendering process renders everything in
>the order: { polygon, line, point } regardless of layer=. This means it
>is possible to place one area over another area, but is it not possible
>to place an area over the top of a road. I think I've seen people do
>this for tunnels and I don't think this will work with mapnik.
>
>	Jon
>

Thanks John, and limitation noted.

Cheers

Andy

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk