function [hdop] = get_dop(H)
%求衛星的gdop值
G=inv(H'*H);
% gdop=sqrt(trace(G));
% pdop = sqrt(G(1,1)+G(2,2)+G(3,3));
hdop = sqrt(G(1,1)+G(2,2));
% vdop = sqrt(G(3,3));
% c = 3e8;
% tdop = sqrt(G(4,4))/c;



% l = length(G);
% temp = 0;
% for i = 1:l-1
%     temp = temp+G(i,i)^2;
% end
% pdop = sqrt(temp);