Hello everyone, I would like to mention that I have committed a new feature to mod_tile / renderd and would appreciate any feedback or comments.
Mod_tile and renderd are now prepared for the possibility to parameterize the mapnik style-sheet on the fly on a (meta)tile by (metatile) basis. For this purpose, the URL schema for tileservers was extended. It now takes the form: https://my.tile.server/style/parameters/z/x/y.ext parameters is an arbitrary string that gets passed on to renderd and can be used to parameterize the style-sheet for that rendering request. The first use for this functionality is to make it easy to offer multi-lingual maps. I.e. to be able to specify (parameterize) the language in which the names should appear on the map. E.g. one can specify that English names (name:en) should be used instead of the plain name tag. This is heavily based upon Jochen Topf's work on the multi-lingual project for wikimedia [1,2], that has shown the feasibility of this concept. By integrating it into mod_tile / renderd and making it trivial to enable, it will hopefully see wider adoption and prove useful to a bigger audience. You can specify an ordering of name tags to be used when trying to render any labels. E.g. de,en,_ will use name:de if available, otherwise try name:en and finally use name if neither name:de or name:en is available. Technically, renderd will take the stylesheet it loads and replace name in the sql queries with coalesce(tags->'name:de', tags->'name:en', tags->'name') as name. Everything should be backwards compatible and one can activate this feature on a style-by-style basis. If not activated, the old URL schema continues to be used. So e.g. a server can support https://my.tile.server/osm/0/0/0.png and https://my.tile.server/osm-multilingua/de,en,_/0/0/0.png. To make this possible, the protocol between mod_tile and renderd was extended to include the parameterization string (as well as pass through mime information for future purposes, e.g. to be able to render both png and jpg). However, again, everything (both mod_tile and renderd) should be backwards compatible. I.e. renderd can receive rendering requests with the previous version of the protocol, in case you only want to update renderd and still have an older version of mod_tile (or indeed another server software or utility for issuing render requests). Likewise, mod_tile can still send the requests in the previous protocol, and indeed will do so by default unless the parameterization feature is explicitly activated for the given style. This should ensure compatibility with tirex, that has not yet been updated to the change in protocol. Although its first use is for the multi-lingual maps, hopefully this feature can be used for other purposes as well. You still need to write code to interpret the parameterization string and apply the transformation to the mapnik stylesheet object, but given that is all encapsulated in a separate file, this will hopefully be relatively easy if one needs it. Kai [1] http://blog.jochentopf.com/2012-06-21-wikipedia-multilingual-maps-project.html [2] http://blog.jochentopf.com/2012-12-19-status-of-the-multilingual-maps-project.html _______________________________________________ dev mailing list [email protected] https://lists.openstreetmap.org/listinfo/dev
