hmat.m

GPS software toolbox for GPS receiver development

%                                hmat.m
%  Scope:   This MATLAB macro constructs the H matrix (based on line-of-sight
%           measurements), when the user's position and the satellites position 
%           are known.
%  Usage:   [houtput,ier] = hmat(svpos,upos)
%  Description of parameters:
%           svpos   - input, four ECEF satellite positions, each row contains
%                     the three component for a satellite, all components are
%                     in meters
%           upos    - input/output, ECEF user's position, the components are 
%                     in meters
%           houtput - output, H matrix (based on line-of-sight measurement)
%           ier     - output, index of error
%                     = 0  no error
%                     = 1  error, see the measurement dimensions  
%  Remark:  At least 4 measurements are required for the construction of H 
%           matrix.
%  Last update:  06/14/00
%  Copyright (C) 1997-00 by LL Consulting. All Rights Reserved.

function  [houtput,ier] = hmat(svpos,upos)

ier = 0;
[nrow,ncol] = size(svpos);
if  (nrow < 4) | (ncol ~= 3)
   ier = 1;
   houtput = 0;
   return;
end

%  Form the matrix H (based on line-of-sight measurements) 

for k = 1:nrow
   temp(1) = upos(1) - svpos(k,1);
   temp(2) = upos(2) - svpos(k,2);
   temp(3) = upos(3) - svpos(k,3);
   tempt = sqrt(temp(1)*temp(1) + temp(2)*temp(2) + temp(3)*temp(3));
   for kk = 1:3
      houtput(k,kk) = temp(kk)/tempt;
   end
   houtput(k,4) = 1.;
end