Scale/zoom levels and tiling are essential for mapping servers, especially if pretending on streaming transmission model. In case of a vector/parametric data transmission service the scale levels’ generation and the tiling of these, as a rule, is performed in quite a different way compared to the traditional raster format based service (keep in mind that a well constructed vector format may 20 – 40 TIMES be smaller than the corresponding PNG raster format for the same content). We do an OSM vector transmission based service for mobile apps (see www.fasterimaging.com).
As someone properly emphasized a clipping is essential for any vector tiling. But, while clipping of line-work objects (roads, streets, borders …) is rather trivial, clipping of area objects is somewhat more complex and complicated issue. Besides the clipping, some kind of area reconstruction/restructuring has to be done (one container area may be clipped into many parts, the same with the corresponding holes, the restructuring has to decide which new holes are in which new areas, than the issue of trivial tiles or empty tiles and tiles inside areas and so on). Also, tiling inevitably results in a considerably larger data amount compared to the original dataset. So, the question is – is it possible to provide a server that combines the tiling’s efficiency and the data size at certain, close to optimal, level. Fortunately, latest research and an experimental version of such a server show that the answer is yes. The experiments are performed on OSM vector data for Europe from some weeks ago (Roughly 30 object classes/layers, 12 area classes like rivers, lakes, forests, sea …, 12 line-work classes like roads, streets, paths, water lines … and some point object classes. POIs and LBSs are overlays on such a base map). The estimates also show that such a very simple server (no DB, no caching …) is fully realistic with extraordinary performance (respond to tens of thousands requests per second) and scalability (just make a new copy as needed). A white paper, describing in more details the above subject, is available. Though in bullets format with many illustrations and with a working title – Hybrid data format, multi tiling and a new server model. Interested? Sandor
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