The minimum tile size is a constant defined in the

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Unformatted text preview: reducers). The minimum tile size is a constant defined in the code which is the smallest width and height in degrees of lat/lon (we assume these are equal in nature) which corresponds to an individual tile. Do not change this constant, as changing this determines how fine the tile grid is, and has a dramatic effect on cluster utilization. Each tile is defined to be 256 x 256 pixels. The zoom level is an integer >= 1, which is an exponential multiplier of the minimum tile size that determines how much land area is rendered onto a tile. At zoom level 1, the minimum tile size of land area is rendered onto a 256x256 pixel tile; this gives the closest zoom and the most detailed features. At zoom level 2, we take 2x the longitude in width, and 2x the latitude in height, and render that much land onto the same sized tile image. Zoom level 3 is 4x the width, 4x the height (16x the area), etc. One of the components you must implement is a tile set divider which, given the number of reducers, the mappable range, and the intended zoom level to render, will break the mappable range into tiles, assign them tile IDs, and group the tile IDs into as many tile sets as there are reducers. This tile set divider is responsible for maintaining a 2-way mapping: it must be able to return a tile ID for any (lat, lon) in the mappable range, and given a tile ID, it must return the (lat, lon) of the northwest (top-left) corner of its tile extent. (Note that this is not neccessarily a direct inverse operation.) This figure shows a mappable range broken up into several tiles (only some of the tiles are drawn in). The tiles have been broken up into two tile sets, "A" and "B." Tiles in the same tile set have the same background color. The mappable range is a square of (lat, lon) coordinates, as are each tile. The tile set divider determined the number of tiles to build based on the zoom level provided as an initialization parameter. The same mappable range (e.g., "the United States") will be passed through the render process several times, one...
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This homework help was uploaded on 04/02/2014 for the course CSE 490 taught by Professor Staff during the Fall '08 term at University of Washington.

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