LatLongTools.py

   1 #
   2 # vi: set softtabstop=4 shiftwidth=4 tabstop=8 expandtab:
   3
   4 import math
   5
   6 def latdist(lat1, lat2):
   7     return (lat1 - lat2) * 111.325
   8
   9 def longdist(lat, long1, long2):
  10     return (long1 - long2) * math.cos(lat / 180.0 * math.pi) * 111.325
  11
  12 def locdist(loc1, loc2):
  13     """terrible approximation"""
  14     xdist = longdist(loc1.latitude, loc1.longitude, loc2.longitude)
  15     ydist = latdist(loc1.latitude, loc2.latitude)
  16     return math.sqrt(xdist * xdist + ydist * ydist)
  17
  18 def findCorners(center, entries):
  19     """Takes a list of two-element tuples: (location, tag).
  20        Returns a four-element list, one for each corner (northwest,
  21        northeast, southwest, southeast). Each element is in turn a list of
  22        tags, sorted by descending distance from the center."""
  23
  24     # Split by nearest corner
  25     splitEntries = [[], [], [], []]
  26     for entry in entries:
  27         if entry[0].latitude >= center.latitude:
  28             if entry[0].longitude <= center.longitude:
  29                 splitEntries[NORTHWEST].append(entry)
  30             else:
  31                 splitEntries[NORTHEAST].append(entry)
  32         else:
  33             if entry[0].longitude <= center.longitude:
  34                 splitEntries[SOUTHWEST].append(entry)
  35             else:
  36                 splitEntries[SOUTHEAST].append(entry)
  37
  38     for corner in splitEntries:
  39         # Descending sort by distance from center.
  40         corner.sort(None, lambda entry: locdist(entry[0], center), True)
  41
  42     # Return the tags.
  43     return [[entry[1] for entry in corner] for corner in splitEntries]
  44
  45 NORTHWEST = 0
  46 NORTHEAST = 1
  47 SOUTHWEST = 2
  48 SOUTHEAST = 3