%                           elevaz.m
%  Scope:   This MATLAB macro computes the elevation angle, the azimuth angle,
%           ECEF unit line-of-sight vector and the range, when the ECEF user
%           and satellite positions are known; WGS-84 constants are used.
%  Usage:   [eangle,az,ulos,range] = elevaz(user,sv)
%  Description of parameters:
%           user   -  input, ECEF user position vector
%           sv     -  input, ECEF satellite position vector
%           eangle -  output, elevation angle in radians
%           az     -  output, azimuth angle in radians
%           ulos   -  output, ECEF unit line-of-sight vector
%           range  -  output, range from user to satellite 
%  Remark:  The components of the input vectors and the range should have the
%           same unit, e.g. meter, foot.
%  External Matlab macros used:  tecefgd, vecefenu, wgs84con
%  Last update:  06/07/99
%  Copyright (C) 1996-99 by LL Consulting. All Rights Reserved.

function  [eangle,az,ulos,range] = elevaz(user,sv)

temp = sv - user;
range = sqrt(temp' * temp);           %  range
ulos = temp / range;                  %  ECEF unit line-of-sight

[ulat,ulon,ualt] = tecefgd(user);     %  user's geodetic coordinates

ulosenu = vecefenu(ulos,ulat,ulon);   %  ENU unit line-of-sight 
eangle = asin(ulosenu(3));            %  elevation angle
az = atan2(ulosenu(1),ulosenu(2));    %  azimuth angle