function distance = dec_deg_to_miles_arcmap(x,y)

% This version switchs coords from (lat,lon) to (lon,lat) to be consistent
% with ARCMAP

% DEC_DEG_TO_MILES calculates great-circle distance in miles between two points
% with coordinates in decimal degrees.

%INPUTS: x = (x1,x2) = [lat1,lon1] in decimal degrees
%        y = (y1,y2) = [lat2,lon2] in decimal degrees

%%EXAMPLE: From: San Francisco (x = [37.68,-122.308]) 
%            To: New York (y = [40.670,-73.944])
% 
% dist = great_circle(x,y)
% 
% dist = 2565.9 (miles)

%*************************************************************
% NOTE: Often decimal degrees are represented as 

%  L1 = (x1,y1) = [lon1,lat1]; L1 = (x2,y2) = [lon2,lat2];

% So one must be careful as to how the coordinates are ordered.
%**************************************************************

% lat1 = x(1);
% lon1 = x(2);
% lat2 = y(1);
% lon2 = y(2);

if norm(x-y) > 0  % This "if" avoids complex values at x == y
     
    lat1 = x(2);
    lon1 = x(1);
    lat2 = y(2);
    lon2 = y(1);

    theta = lon1 - lon2;
    dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) + ...
        cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta));
    dist = acos(dist);
    dist = rad2deg(dist);
    distance = dist * 60 * 1.1515;
    
else % x == y
    
    distance = 0;
    
end