Source code for synapse.lib.gis

import math

'''
Synapse module with helpers for earth based geo-spacial calculations.
'''

# base earth geo distances will be in mm
r_mm = 6371008800.0
r_km = 6371.0088

# investigate perf impact of using WGS-84 ellipsoid for dist calc

[docs]def latlong(text): ''' Chop a latlong string and return (float,float). Does not perform validation on the coordinates. Args: text (str): A longitude,latitude string. Returns: (float,float): A longitude, latitude float tuple. ''' nlat, nlon = text.split(',') return (float(nlat), float(nlon))
[docs]def near(point, dist, points): ''' Determine if the given point is within dist of any of points. Args: point ((float,float)): A latitude, longitude float tuple. dist (int): A distance in mm ( base units ) points (list): A list of latitude, longitude float tuples to compare against. ''' for cmpt in points: if haversine(point, cmpt) <= dist: return True return False
[docs]def haversine(px, py, r=r_mm): ''' Calculate the haversine distance between two points defined by (lat,lon) tuples. Args: px ((float,float)): lat/long position 1 py ((float,float)): lat/long position 2 r (float): Radius of sphere Returns: (int): Distance in mm. ''' lat1, lon1 = px lat2, lon2 = py dlat = math.radians(lat2 - lat1) dlon = math.radians(lon2 - lon1) lat1 = math.radians(lat1) lat2 = math.radians(lat2) a = math.sin(dlat / 2) ** 2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon / 2) ** 2 c = 2 * math.asin(math.sqrt(a)) return c * r
[docs]def bbox(lat, lon, dist): ''' Calculate a min/max bounding box for the circle defined by lalo/dist. Args: lat (float): The latitude in degrees lon (float): The longitude in degrees dist (int): A distance in geo:dist base units (mm) Returns: (float,float,float,float): (latmin, latmax, lonmin, lonmax) ''' latr = math.radians(lat) lonr = math.radians(lon) rad = r_mm prad = rad * math.cos(latr) latd = dist / rad lond = dist / prad latmin = math.degrees(latr - latd) latmax = math.degrees(latr + latd) lonmin = math.degrees(lonr - lond) lonmax = math.degrees(lonr + lond) return (latmin, latmax, lonmin, lonmax)
[docs]def dms2dec(degs, mins, secs): ''' Convert degrees, minutes, seconds lat/long form to degrees float. Args: degs (int): Degrees mins (int): Minutes secs (int): Seconds Returns: (float): Degrees ''' return degs + (mins / 60.0) + (secs / 3600.0)