calculating a gps coordinate given a point, bearing and distance

Question

I have a problem which draws my back in some project for some time now.

I'm basically looking to trap a polygon using x, y points drawn by some script I've written. lat, lon are the center GPS cords of the polygon and I'm looking for its surrounding polygon.

here is a part of my code in python:

def getcords(lat, lon, dr, bearing):
    lat2=asin(sin(lat)*cos(dr)+cos(lat)*sin(dr)*cos(bearing))
    lon2=lon+atan2(sin(bearing)*sin(dr)*cos(lat),cos(dr)-sin(lat)*sin(lat2))
    return [lat2,lon2]

my input goes like this:

• lat, lon - are given in decimal degrees.
• dr - is the angular computed by dividing the distance in miles by the earth's -radius(=3958.82)
• bearing - between 0-360 degrees.

However for the input:

getcorsds1(42.189275, -76.85823, 0.5/3958.82, 30)

I get output: [-1.3485899508698462, -76.8576637627568], however [42.2516666666667, -76.8097222222222] is the right answer.

as for the angular distance, I calculate it simply by dividing the distance in miles by the earth's radius(=3958.82).

anybody?

Answer 1

With geopy v2.0.0 (+ kilometers instead miles)

from geopy import Point                                                                                                                                                                       
from geopy.distance import geodesic                                                                                                                                                           
                                                                                                                                                                                              
distKm = 1                                                                                                                                                                                    
lat1 = 35.68096477080332                                                                                                                                                                      
lon1 = 139.76720809936523                                                                                                                                                                     
                                                                                                                                                                                              
print('center', lat1, lon1)                                                                                                                                                                   
print('north', geodesic(kilometers=distKm).destination(Point(lat1, lon1), 0).format_decimal())                                                                                                
print('east', geodesic(kilometers=distKm).destination(Point(lat1, lon1), 90).format_decimal())                                                                                                
print('south', geodesic(kilometers=distKm).destination(Point(lat1, lon1), 180).format_decimal())                                                                                              
print('west', geodesic(kilometers=distKm).destination(Point(lat1, lon1), 270).format_decimal()) 

result is

center 35.6809647708 139.767208099
north 35.6899775841, 139.767208099
east 35.680964264, 139.778254714
south 35.6719519439, 139.767208099
west 35.680964264, 139.756161485