%                              vecefeci.m
%  Scope:   This MATLAB macro performs the transformation from ECEF to ECI
%           (Earth Centered Inertial) coordinates for a given position vector
%           and time elapsed since reference time; WGS-84 earth's rotation 
%           rate constant is used.
%  Usage:   peci = vecefeci(pecef,dtime)
%  Description of parameters:
%           pecef -  input, ECEF position vector (with components in meters)
%           dtime -  input, time elapsed since reference time in seconds
%           peci  -  output, ECI position vector, with components in 
%                    same units as the input ECEF position vector
%  Remarks: The ECEF to ECI transformation takes into account only Earth's 
%           rotation, i.e. no Earth's precession and mutation effects.
%  External Matlab macros used:  wgs84con
%  Last update:  04/05/00
%  Copyright (C) 1997-00 by LL Consulting. All Rights Reserved.

function   peci = vecefeci(pecef,dtime)

wgs84con;
% global constants used: rot_rate (WGS-84 earth's rotation rate, in rad/sec)

swie = sin(rot_rate*dtime);
cwie = cos(rot_rate*dtime);

peci = zeros(3,1);
peci(1) = pecef(1) * cwie - pecef(2) * swie;
peci(2) = pecef(1) * swie + pecef(2) * cwie;
peci(3) = pecef(3);