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metteo / geomodel

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Please document relationship between resolution and box size #22

Open GoogleCodeExporter opened 9 years ago

GoogleCodeExporter commented 9 years ago 
I want to create my own simple query to check if a point is in a box. Can you 
please document the relationship between the resolution (i.e. the length of the 
Geocell string) and the box size (even approximately) e.g. a 13 character cell 
is 100 meters x 100 meters, a 12 char is 400 x 400m etc.

Thanks for the great project!

Original issue reported on code.google.com by marc1hac...@gmail.com on 4 Aug 2010 at 11:49

GoogleCodeExporter commented 9 years ago 
Way late for the asker I'm sure, but I was curious about this as well.
The distance between two degrees of longitude depend greatly on the value, 
since the earth is, you know, a sphere. Latitude is pretty consistent though. 
For these calculations I assumed we're at the equator. Below is a table of the 
resolution (number of characters) in a geocell to the latitudinal (top to 
bottom) distance in meters. Disclaimer: I wouldn't bet my life on these 
figures, and neither should you.

13: 0.30
12: 1.19
11: 4.75
10: 18.98
9: 75.93
8: 303.70
7: 1,214.81
6: 4,859.22
5: 19,436.88
4: 77,747.54
3: 310,990.14
2: 1,243,960.57
1: 49,75,842.27

And here's the same table for longitude at the equator:
13: 0.60
12: 2.39
11: 9.55
10: 38.22
9: 152.87
8: 611.50
7: 2,445.98
6: 9,783.94
5: 39,135.75
4: 156,542.99
3: 626,171.95
2: 2,504,687.81
1: 10,018,751.22

And at 45 degrees latitude:
13: 0.42
12: 1.69
11: 6.77
10: 27.07
9: 108.28
8: 433.12
7: 1,732.47
6: 6,929.90
5: 27,719.58
4: 110,878.32
3: 443,513.28
2: 1,774,053.13
1: 7,096,212.51

Original comment by skl...@gmail.com on 5 Sep 2013 at 12:37