xsvsel.m

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%                             xsvsel.m
%  Scope:   This MATLAB program executes the selection of 4, 5 or 6 satel- 
%           lites based on minimum geometric dilution of precision (GDOP)
%           from all possible sets available. For the selected set of 4, 5
%           or 6 satellites, and all-in-view, the computed dilution-of-
%           precision (DOP) values are outputted.
%  Usage:   xsvsel
%  Inputs:  - name of the input filename; the default is xsvsel1.dat
%           - name of the output filename or display the results on screen
%           - number of satellites to be selected
%  Outputs: - number of satellites available
%           - number of satellites to be used 
%           - indices of the selected satellites 
%           - dilution-of-precision (DOP) values for the selected satellites
%             set
%  External Matlab macros used:  svsel4, svsel5, svsel6, dop1
%  Last update:  06/14/00
%  Copyright (C) 1996-00 by LL Consulting. All Rights Reserved.

clear  
yes = 'y';

%  Read the input data file

disp('  ');
disp('Enter input filename - the default is datafile xsvsel1.dat');
disp('  ');
answer1 = input('Do you want to use the default datafile? (y/n)[n] --> ','s');
disp('  ');
if (strcmp(answer1,yes) == 1)
   f1 = 'xsvsel1.dat';
else
   f1 = input('Specify the input filename (with extension) -->  ','s');
   disp('  ');
end
g = load(f1);
[nrow,ncol] = size(g);
if  ncol ~= 3
   disp('  ');
   clear xsvsel1.dat    %  when xsvsel.dat is selected as an input datafile
   error('Error 1  -  XSVSEL; the input data file does not have 3 columns');
end

%  Enter the name of the output data file

answer2 = input('Do you want to save the data (default, on screen)? (y/n)[n] --> ','s');
disp('  ');
if (strcmp(answer2,yes) == 1)
   f2 = input('Specify the output filename, e.g. xsvsel1.out  -->  ','s');
   disp('  ');
else   
   f2 = 1;
end

answer3 = 'y';
while (strcmp(answer3,yes) == 1)
   clear  index dops svind
   index = input('Specify the number of satellites to be selected -->   ');
   disp('  ');
   if  index >= 7    
      index = nrow;   %  all-in-view case
   end

%  Select the best satellites

   if  index == 4
      [hmat,dops,svind] = svsel4(g');
   elseif  index == 5
      [hmat,dops,svind] = svsel5(g');
   elseif  index == 6
      [hmat,dops,svind] = svsel6(g');
   elseif  index >= 7     %  all-in-view case
      dops = dop1(g);
      for  k = 1:index
         svind(k) = k;
      end
   else
      disp('  ');
      clear xsvsel.dat    %  when xsvsel.dat is selected as an input datafile
      error('Error 2  -  XSVSEL ; check the number of LOSs or selection index');
   end

%  Record the results

   fprintf(f2,'**************************************************************');
   fprintf(f2,'\n\nNumber of satellites available   = %3.0f\n',nrow);
   fprintf(f2,'Number of satellites to be used  = %3.0f\n',index);
   fprintf(f2,'Indices of the selected satellites = ');
   for k = 1:index
      fprintf(f2,'%3.0f ',svind(k));
   end
   fprintf(f2,'\nGDOP = %10.3f',dops(1));
   fprintf(f2,'\nPDOP = %10.3f',dops(2));
   fprintf(f2,'\nHDOP = %10.3f',dops(3));
   fprintf(f2,'\nVDOP = %10.3f',dops(4));
   fprintf(f2,'\nTDOP = %10.3f\n\n',dops(5));
   fprintf(f2,'**************************************************************');
   fprintf(f2,'\n\n');
   
%  Select another computation, if desired

   answer3 = input('Do you want another selection? (y/n)[n] --> ','s');
   disp('  ');

end

clear xsvsel.dat    %  when xsvsel.dat is selected as an input data file
disp('End of the program  XSVSEL');
disp('  ');