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Slippy Maps

Slippy Maps. Visualizing maps on the web. What is a Map?. A map is a drawing that is the representation, on a certain scale, of a terrain. The classic "Big (Composite) Map". Have a very big file size for the "real-estate" you get in the game world. Have limits with texture sizes.

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Slippy Maps

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  1. Slippy Maps Visualizing maps on the web

  2. What is a Map? • A map is a drawing that is the representation, on a certain scale, of a terrain.

  3. The classic "Big (Composite) Map" • Have a very big file size for the "real-estate" you get in the game world. • Have limits with texture sizes. • Not be very flexible; you won't really be able to re-use whole screens as different parts of the world. • Be easier to program with. • Won't require a 'Tile Editor' to compose.

  4. "Tiled Map“ • Have a much smaller file size for a much larger world. • Be a bit more fiddly to program (but it's not massively complex). • Require you to edit / load tile configurations (maps) in the game from your own file format. • Make large scrolling levels work much better. • Have much more flexibility - one tile set could make dozens of levels.

  5. Requesting for a Map • The map will be generated with a proper level of detail, depending on the following parameters: • latitude and • longitude for the center of map • the zoom level – corresponding on how much space to be represented on a usually preset content size. The level of detail is then deducted, depending on how much information can be represented with the above constraints.

  6. Map Services Providers • Free: OpenStreetMap • Commercial: Google (Tele Atlas) TomTom

  7. OpenStreetMap • OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world – www.openstreetmap.org. • The data comes from: • Portable GPS devices, • aerial photography, • from other free sources, • or simply from local knowledge.

  8. OpenStreetMap • OpenStreetMap was inspired by sites such as Wikipedia — the map display features a prominent 'Edit' tab and a full revision history is maintained. Registered users can upload GPS track logs and edit the vector data using the given editing tools.

  9. OpenStreetMap – Map Production • The initial map data was all built from scratch by volunteers performing ground surveys using a GPS unit and a notebook or a voice recorder. Then the data was then entered into the OpenStreetMap database. • In the present the availability of aerial photography and other data sources has greatly increased the work speed the data is collected more accurately. • Ground surveys are performed by volunteers. The data is entered into the database using one of several purpose-built map editors.

  10. Slippy Map • The Slippy Map is the main OpenStreetMap web based display for browsing OSM data. • AJAX component : JavaScript runs in the browser, which dynamically requests tiles from the server in the background without reloading the whole HTML page. This provides a smooth slippyzoomy map browsing experience.

  11. Tile Rendering • The tiles are pre-rendered and stored on disk in 2 sets: • Tiles rendered by Mapnik • Osmarender renderings (produced by tiles@home)

  12. Different Tile Renderings • The maps are rendered as raster images called tiles as a result of fetching the map data via the API. Mapnik Osmarender CloudMade

  13. Mapnik Tile Rendering • Mapnik tiles are currently generated on tile.openstreetmap.org. • The Mapnik database is updated with hourly diffs so that most data changes should get rendered within an hour. • Mapnik rendering runs as an apache module called mod tile developed especially for high performance needs.

  14. Mapnik Renderer Rules • Every tile has a timestamp for when it was rendered and a dirty flag signifying that it is ready to be re-rendered. • Whenever looking at a tile, it is checked if it is older than seven days. • If it is older than seven days then it is marked dirty (and thus rendered). • A background rendering process generates a list of all dirty tiles and then proceeds to render them all. • Once it has finished it queries the list of dirty tiles again. • Tiles are rendered on a interest/attention-first basis. • Marking a tile dirty does not mark all sub tiles as dirty.

  15. Libraries for Displaying the Tiles • OpenLayers and GoogleMaps • OpenLayers can combine maps from different sources (Google Maps background, WMS overlays, vector data from KML or GML files or WFS etc) • You can style OpenLayers much more than possible with Google Maps • OpenLayers is open source, so debugging is possible • If maps with high precision are requested, the best choice is using OpenLayers with a suitable map server backend rather than Google Maps to get a better map projection (Google Maps uses the Mercator projection, so it cannot show areas around the poles)

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