function  ECEF_pos = lla2ecef(lat, lon, alt)%% function  ECEF_pos = lla2ecef(lat, lon, alt)%% This function converts from geodetic coordinates (longitude,% latitude, and altitude) to an ECEF position vector.%% Input parameters:%   lon : WGS-84 geodetic longitude (rad)%   lat : WGS-84 geodetic latitude (rad)%   alt : WGS-84 ellipsoidal altitude (m)%% Output parameter:%   ECEF_pos : ECEF position vector (m)%% initial conditionsa = 6378137;e2 = 0.00669437999013;rn = a/sqrt(1-e2*(sin(lat))^2);R = (rn + alt)*cos(lat);ECEF_pos = [R*cos(lon), R*sin(lon), (rn*(1-e2) + alt)*sin(lat)];