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This is a slippy map for the iPhone written by Joseph Gentle.
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It has been made as part of the CatchMe project.
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We released it for you under the BSD license.
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---------
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For Users
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---------
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Once this application has more functionality than google maps, I'll throw it on the itunes store for free.
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--------------
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For developers
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--------------
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- Don't be frightened by so many source code files! Most of them (144 of the ~160 source code files) are from the Proj4 library. Proj4 is available here:
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http://trac.osgeo.org/proj/
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The only thing proj4 is used for here is converting Longitude / lattitude coordinates into Mercator coordinates (and back again).
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Coordinate Systems
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- This project uses 4 different coordinate systems! The code won't make any sense unless you understand them:
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Longitude / Lattitude
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- Points around the spherical earth measured in Degrees.
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- Using the types provided by CoreLocation - CLLocationCoordinate2D { double lat, long; }
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Mercator coordinates
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- These are points on a flat square. The units are metres; though they're only accurate near the equator.
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- Using types in Mercator.h - MercatorPoint { double x, y; } and MercatorRect.
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http://en.wikipedia.org/wiki/Mercator_projection
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Tile coordinates
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- Each zoom level (z) has a grid of 2^z x 2^z tiles. Using OpenStreetMaps each of these tiles is 256 pixels per side.
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- Each tile is indexed by the Tile struct - { int x, y, zoom; }. There are also TilePoint and TileRect structs for discussing regions of tiles complete with offsets into the tiles.
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Screen Coordinates
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- These are measured in pixels within the bounds of the MapView.
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- Using builtin CGPoint, CGSize and CGRect
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You can convert:
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lat/long <-> Mercator using: [Mercator toLatLong: (MercatorPoint) coordinate] and [Mercator toMercator: (CLLocationCoordinate2D) coordinate]
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Mercator <-> Tile using FractalTileProjection
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Tile <-> Screen coordinates using ScreenProjection
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Always be aware of what coordinate system you're working in / with and the code is all pretty easy.
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Desired Features
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Search
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Overlays (Of course, these can just be done with cocoa at the moment)
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Remember last location
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Disk cache
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A Geo tracing facility would be nice... though I'm not too sure how the user can get the geotraces back off the device. |
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\ No newline at end of file |
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