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51 lines
1.6 KiB
Python
51 lines
1.6 KiB
Python
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# coding=utf-8
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__all__ = ["clamp", "haversine", "get_zoom_for_radius"]
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from math import asin, cos, pi, radians, sin, sqrt
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from kivy.core.window import Window
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from kivy.metrics import dp
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def clamp(x, minimum, maximum):
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return max(minimum, min(x, maximum))
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def haversine(lon1, lat1, lon2, lat2):
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"""
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Calculate the great circle distance between two points
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on the earth (specified in decimal degrees)
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Taken from: http://stackoverflow.com/questions/4913349/haversine-formula-in-python-bearing-and-distance-between-two-gps-points
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"""
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# convert decimal degrees to radians
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lon1, lat1, lon2, lat2 = map(radians, [lon1, lat1, lon2, lat2])
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# haversine formula
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dlon = lon2 - lon1
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dlat = lat2 - lat1
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a = sin(dlat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(dlon / 2) ** 2
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c = 2 * asin(sqrt(a))
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km = 6367 * c
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return km
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def get_zoom_for_radius(radius_km, lat=None, tile_size=256.0):
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"""See: https://wiki.openstreetmap.org/wiki/Zoom_levels"""
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radius = radius_km * 1000.0
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if lat is None:
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lat = 0.0 # Do not compensate for the latitude
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# Calculate the equatorial circumference based on the WGS-84 radius
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earth_circumference = 2.0 * pi * 6378137.0 * cos(lat * pi / 180.0)
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# Check how many tiles that are currently in view
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nr_tiles_shown = min(Window.size) / dp(tile_size)
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# Keep zooming in until we find a zoom level where the circle can fit inside the screen
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zoom = 1
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while earth_circumference / (2 << (zoom - 1)) * nr_tiles_shown > 2 * radius:
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zoom += 1
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return zoom - 1 # Go one zoom level back
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