utc2gps.m

此功能包用于各种GPS坐标和时间的转换

function [GPS_week, GPS_sec, GPS_day] = utc2gps(UTC_time,leap_sec)

% [GPS_week, GPS_sec, GPS_day] = utc2gps(UTC_time,leap_sec);
%                          or
% GPS_time = utc2gps(UTC_time,leap_sec); 
%  
% where GPS_time = [GPS_week GPS_sec] (nx2)
%
% Converts a UTC time matrix to the equivalent time in GPS weeks,
% GPS seconds, and GPS days (GPS time started at 00:00:00 6 JAN 1980)
%
% Input:  
%   UTC_time - matrix of the form [year month day hour minute second] (nx6)
%               with 4-digit (1980) or 2-digit (80) years,
%               valid years are 1980 - 2079 (2-digit 80-79)
%   leap_sec - leap seconds applied to UTC relative to GPS (optional)
%               can be a 1x1 or an nx1, if not entered the function will
%               use a look-up table to determine the number of leap seconds
% Output: 
%   GPS_week - GPS week (nx1) (if 0 or 1 output parameters are used,
%               this is filled with [GPS_week GPS_sec] (nx2).  See the 
%               alternative calling option from above.
%               GPS week values are kept in linear time without the 1024 rollovers
%               (e.g. UTC time [1999 10 1 0 0 0] = GPS time [1029 432013])
%               use the MATLAB "mod" function to obtain 1024 based weeks
%                  new_GPS_week = mod(GPS_week,1024);
%   GPS_sec  - seconds into the week measured from Sat/Sun midnight (nx1)
%   GPS_day  - days since the beginning of GPS time (optional) (nx1)
%
% See also GPS2UTC, GPS2LEAP

% Written by: Maria Evans/Jimmy LaMance 10/9/96
% Copyright (c) 1998 by Constell, Inc.

% functions called: ERR_CHK, UTC2LEAP

%%%%% BEGIN VARIABLE CHECKING CODE %%%%%
% declare the global debug variable
global DEBUG_MODE

% Initialize the output variables
GPS_week=[]; GPS_sec=[]; GPS_day=[];

% Check the number of input arguments and issues a message if invalid
msg = nargchk(1,2,nargin);
if ~isempty(msg)
  fprintf('%s  See help on UTC2GPS for details.\n',msg);
  fprintf('Returning with empty outputs.\n\n');
  return
end

% Check for 2-digit years
I_2 = find(UTC_time(:,1) < 100);
if ~isempty(I_2)   
  I_1900 = find(UTC_time(I_2,1) >= 80);
  I_2000 = find(UTC_time(I_2,1) < 80);
  if ~isempty(I_1900)
    UTC_time(I_2(I_1900),1) = UTC_time(I_2(I_1900),1) + 1900;
  end 
  if ~isempty(I_2000)
    UTC_time(I_2(I_2000),1) = UTC_time(I_2(I_2000),1) + 2000;
  end                                                     
end
  
if nargin < 2 & size(UTC_time,2) == 6
  leap_sec = utc2leap(UTC_time); 
elseif nargin < 2 & size(UTC_time,2) ~= 6 
  leap_sec = ones(size(UTC_time,1),1) * leap_sec;
end % if             

% Get the current Matlab version
matlab_version = version;
matlab_version = str2num(matlab_version(1));

% If the Matlab version is 5.x and the DEBUG_MODE flag is not set
% then set up the error checking structure and call the error routine.
if matlab_version >= 5.0                        
  estruct.func_name = 'UTC2GPS';

  % Develop the error checking structure with required dimension, matching
  % dimension flags, and input dimensions.
  estruct.variable(1).name = 'UTC_time';
  estruct.variable(1).req_dim = [901 6];
  estruct.variable(1).var = UTC_time;
  
  estruct.variable(2).name = 'leap_sec';
  estruct.variable(2).req_dim = [901 1; 1 1];
  estruct.variable(2).var = leap_sec;
 
  % Call the error checking function
  stop_flag = err_chk(estruct);
  
  if stop_flag == 1           
    fprintf('Invalid inputs to %s.  Returning with empty outputs.\n\n', ...
             estruct.func_name);
    return
  end % if stop_flag == 1
end % if matlab_version >= 5.0 & isempty(DEBUG_MODE) 

%%%%% END VARIABLE CHECKING CODE %%%%%

%%%%% BEGIN ALGORITHM CODE %%%%%
% data matrix with the number of days per month             
% days in full months for leap year
leapdays =   [0 31 60 91 121 152 182 213 244 274 305 335];  
% days in full months for standard year 
noleapdays = [0 31 59 90 120 151 181 212 243 273 304 334];                                                     

% Leap year flag  
% determine which input years are leap years
leap_year = ~rem((UTC_time(:,1)-1980),4);     
I_leap = find(leap_year == 1);                % find leap years
I_no_leap = find(leap_year == 0);             % find standard years

% Round the first column of the almanac to get integer satellite numbers
a_round = ceil(UTC_time(:,2));
d_diff = a_round - UTC_time(:,2);
I_diff_non_zero = find(d_diff ~= 0);
if ~isempty(I_diff_non_zero)
  UTC_time(I_diff_non_zero,2) = a_round(I_diff_non_zero);
  fprintf('Non-integer months numbers have been rounded up in UTC2GPS.\n')
end % if ~isempty(I_diff_non_zero)

% generate a matrix that has the days per completed month for both 
% leap and standard years
if any(I_leap)
  dayspermonth(I_leap) = leapdays(UTC_time(I_leap,2));
end % if any(I_leap)

if any(I_no_leap)
  dayspermonth(I_no_leap) = noleapdays(UTC_time(I_no_leap,2));
end % if any(I_no_leap)

% compute the number of leap days encounted in past years, 
% need to add one to the fix computation to get the year correct                                                         
leapyrs = fix((UTC_time(:,1) - 1980) ./ 4) + eval('~leap_year');

% Compute the number of days in completed years since 1980
gpsday = (UTC_time(:,1) - 1980) .* 365 + leapyrs;
                               
% Add the number of days for each completed month
gpsday = gpsday + dayspermonth';

% add the number of days for each completed day 
% (which is 1 less than the current day)
gpsday = gpsday + (UTC_time(:,3) - 1);

% add the fraction of days for each completed hour (hour/24)
% seconds into the current day (avoids round-off errors)
gpssec = UTC_time(:,4) .* 3600; 

% add the fraction of days for each completed minute (minute/1440)
gpssec = gpssec + UTC_time(:,5) .* 60;

% add the fraction of days each completed second (second/86400)
gpssec = gpssec + UTC_time(:,6);

% Subtract 5 days because the starting date is 00:00 6 January 1980
gpsday = gpsday - 5; 

GPS_day = gpsday;        

% formal return parameter GPS week
GPS_week = fix(GPS_day ./ 7); 
days_into_week = floor(rem(GPS_day,7));

% Add leap seconds to the gps time 
GPS_sec = days_into_week' * 86400 + gpssec' + leap_sec';

% check to make sure the leap seconds don't force a week rollover
I_next = find(GPS_sec >= 86400 * 7);
if any(I_next)
  GPS_week(I_next) = GPS_week(I_next) + 1;
  GPS_sec(I_next) = GPS_sec(I_next) - 86400 * 7;
end % if

% check the output arguments, if the out requested is length 0 ot 1, 
% return GPS week and GPS seconds in a single vector
if nargout == 0 | nargout == 1
  GPS_week = [GPS_week GPS_sec'];
end % if nargout == 0 | nargout == 1

% Return the GPS week, GPS seconds into the week, and the number of 
% completed days (GPS). formal return parameter GPS days since Jan 6 1980
if nargout == 3
  GPS_day = GPS_week * 7 + GPS_sec / 86400;   
end % if nargout == 3                     

%%%%% END ALGORITHM CODE %%%%%

% end UTC2GPS