Added mapview module

sbapp/mapview/utils.py

@@ -0,0 +1,50 @@
+# coding=utf-8
+
+__all__ = ["clamp", "haversine", "get_zoom_for_radius"]
+
+from math import asin, cos, pi, radians, sin, sqrt
+
+from kivy.core.window import Window
+from kivy.metrics import dp
+
+
+def clamp(x, minimum, maximum):
+    return max(minimum, min(x, maximum))
+
+
+def haversine(lon1, lat1, lon2, lat2):
+    """
+    Calculate the great circle distance between two points
+    on the earth (specified in decimal degrees)
+
+    Taken from: http://stackoverflow.com/questions/4913349/haversine-formula-in-python-bearing-and-distance-between-two-gps-points
+    """
+    # convert decimal degrees to radians
+    lon1, lat1, lon2, lat2 = map(radians, [lon1, lat1, lon2, lat2])
+    # haversine formula
+    dlon = lon2 - lon1
+    dlat = lat2 - lat1
+    a = sin(dlat / 2) ** 2 + cos(lat1) * cos(lat2) * sin(dlon / 2) ** 2
+
+    c = 2 * asin(sqrt(a))
+    km = 6367 * c
+    return km
+
+
+def get_zoom_for_radius(radius_km, lat=None, tile_size=256.0):
+    """See: https://wiki.openstreetmap.org/wiki/Zoom_levels"""
+    radius = radius_km * 1000.0
+    if lat is None:
+        lat = 0.0  # Do not compensate for the latitude
+
+    # Calculate the equatorial circumference based on the WGS-84 radius
+    earth_circumference = 2.0 * pi * 6378137.0 * cos(lat * pi / 180.0)
+
+    # Check how many tiles that are currently in view
+    nr_tiles_shown = min(Window.size) / dp(tile_size)
+
+    # Keep zooming in until we find a zoom level where the circle can fit inside the screen
+    zoom = 1
+    while earth_circumference / (2 << (zoom - 1)) * nr_tiles_shown > 2 * radius:
+        zoom += 1
+    return zoom - 1  # Go one zoom level back