![]() ![]() The highest priority is for on -the fly rendering of tiles not yet in the tile cache, two priority levels for re-rendering out of date tiles on the fly and two background batch rendering queues. The renderd daemon implements a queuing mechanism with multiple priority levels to provide an as up-to-date viewing experience given the available rendering resources. renderd passes back the produced tile to the web server and in turn to the browser. renderd is the standard backend currently used by even if some OSM implementations use Tirex Mapnik extracts data from the PostGIS database according to the openstreetmap-carto style information and dynamically renders the tile. Conversely, if the request needs to be rendered, then it is queued to the renderd backend, which is responsible to invoke Mapnik to perform the actual rendering renderd is a daemon process included in the mod_tile sources and interconnected to mod_tile via UNIX queues. When the Apache web server receives a request from the browser, it invokes the mod_tile plugin, which in turn checks if the tile has already been created (from a previous rendering) and cached, so that it is ready for use in case, mod_tile immediately sends the tile back to the web server. OSM.xml is preliminarily produced by a tool named carto from the openstreetmap-carto style (project.mml and all related CartoCSS files included in openstreetmap-carto). Also, a file system directory including the OSM.xml file, map symbols (check openstreetmap-carto/symbols subdirectory) and shapefiles (check openstreetmap-carto/data subdirectory) is needed. ![]()
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