dop2.m

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%                             dop2.m
%  Scope:   This MATLAB macro computes dilution of precision (DOP) quantities
%           when four line-of-sight unit vectors are specified, by using a 
%           direct method.
%  Usage:   dops = dop2(g)
%  Description of parameters:
%           g    - input, line-of-sight unit vectors, each vector is
%                  stored in another row (it should be 3 columns)
%           dops - output, dilution of precision quantities 
%                  dops(1) = geometric dilution of precision (GDOP) 
%                  dops(2) = position dilution of precision (PDOP)
%                  dops(3) = horizontal dilution of precision (HDOP)
%                  dops(4) = vertical dilution of precision (VDOP)
%                  dops(5) = time dilution of precision (TDOP)
%  Last update: 06/14/00
%  Copyright (C) 1996-00 by LL Consulting. All Rights Reserved.

function  dops = dop2(g)

[nrow,ncol] = size(g);
if (ncol ~= 3) | (nrow ~= 4)
   error('Error -  DOP2 ; check the unit line of sight vectors');
end
unitvec = ones(nrow,1);

h = [g unitvec];                              %  form the matrix  H

%  Determine DOP quantities

hinv = inv(h);
dop = hinv * hinv';

dops(1) = sqrt(dop(1,1) + dop(2,2) + dop(3,3) + dop(4,4));    %  GDOP
dops(2) = sqrt(dop(1,1) + dop(2,2) + dop(3,3));               %  PDOP
dops(3) = sqrt(dop(1,1) + dop(2,2));                          %  HDOP
dops(4) = sqrt(dop(3,3));                                     %  VDOP 
dops(5) = sqrt(dop(4,4));                                     %  TDOP