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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.
- Fall '08