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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 – 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 slippy zoomy map browsing experience.

11 Tile Rendering The tiles are pre-rendered and stored on disk in 2 sets: 1. Tiles rendered by Mapnik 2. Osmarender renderings (produced by

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

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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