seleph.m

Sky lab calculate position of satellite in GNSS systems and calculate elevation and azimuth them and

function idx = sateph(prn,t,eph)
%SELEPH  Select satellite ephemeris
%        SELEPH selects the correct satellite ephemeris from eph and returns
%        the row number idx.
%        Syntax:
%                idx = sateph(prn,t,eph)
%        with
%                prn      satellite prn numbers 
%                t        time in seconds into refweek 
%                eph      matrix with ephemeris parameters from RXNAV
%                -------
%                idx      row number of the most recent ephemeris
% 
%        The satellite ephemeris data is stored in eph, idx contains
%        the row number(s) with ephemeris corresponding to the satellite(s)
%        and time(s) given in prn and t.

%        H. van der Marel, LGR, 29-04-95
%        (c) Geodetic Computing Centre, TU Delft


%
% Broadcast Satellite Ephemeris data stored in Eph(_,:)
%
%            name      description
%
% Eph(_, 1)  prn       Satellite prn number
% Eph(_, 2)  toc       Time of clock (seconds into GPS week)
% Eph(_,24)  week      GPS week # (for TOE and TOC)

%
% Declare global GPSWEEK
%

global GPSWEEK;

%
% Loop through all ephemeris sets and select most recent one 
%

[n,m] = size(eph);
dtmin=inf;
idx=-1;
for count=1:n
  if prn==eph(count, 1) 
     dt=abs( t - eph(count,2) + 604800*(GPSWEEK-eph(count,24)));
     if dt<dtmin
        idx=count;
        dtmin=dt;
     end
  end
end