function angle=angsep(x1,y1,x2,y2)
%angsep(lat1,lon1,lat2,long2)
% determines angular separation between two points on Earth
size(x1);size(y1);
a(:,1)=sin((90-x1)*pi/180).*cos(y1*pi/180);
a(:,2)=sin((90-x1)*pi/180).*sin(y1*pi/180);
a(:,3)=cos((90-x1)*pi/180);
b(:,1)=sin((90-x2)*pi/180).*cos(y2*pi/180);
b(:,2)=sin((90-x2)*pi/180).*sin(y2*pi/180);
b(:,3)=cos((90-x2)*pi/180);
cosine=sum((a.*b)')';
angle=acos(cosine)*180/pi;