Changes between Version 4 and Version 5 of ZoomLevels

Timestamp:

Jul 27, 2018 9:01:15 PM (7 years ago)

Author:

Uriel

Comment:

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ZoomLevels

@@ -26 +26 @@
 
 The most data we could possibly waste on the left side of the tile is just about 1 degree. We'll say .999. So if our (fictional) tile at zoom 7 starts at 6.999 degrees, we will still need to load the SRTM data starting at 6.0 to ensure we cover that little bit before 7.0. The right border of our two-tile window is 6.999 + 5.625 = '''12.624 degrees'''. Since our SRTM data needs to overshoot that, our SRTM window must go from 6 to 13 degrees. That's 7 tiles.
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+Starting from 0, how would this play out if it was scripted?
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+1. The first two web tiles run from 0 to 5.625. Our 7 degree window covers 0 to 6, more than enough to capture both tiles. We will be throwing away the data after 5.625, which is not a problem.
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+2. The next two web tiles run from 5.625 to 11.25. We need to start our 7 degree window at 5 to catch the start of the tile, so it covers 5 to 12 degrees. Again we throw away a bit but fully cover two tiles.
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+3. The next two web tiles run from 11.25 to 16.875. Following the pattern, our 7 degree window runs covers 11 to 18 degrees. 
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+4. And so on, starting the each 7 degree window at the rounded-down (westward, really) coordinate of the previously generated tile.