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function [utcTime] = Gps2Utc(gpsTime) |
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% [utcTime] = Gps2Utc(gpsTime) |
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% Convert GPS time (week & seconds) to UTC |
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% |
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% Input: gpsTime, [mx2] matrix [gpsWeek, gpsSeconds], |
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% |
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% Outputs: utcTime, [mx6] matrix = [year,month,day,hours,minutes,seconds] |
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% |
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% Valid range of inputs: |
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% gps times corresponding to 1980/6/1 <= time < 2100/1/1 |
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% i.e. [0,0] <= gpsTime < [6260, 432000] |
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% |
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% See also: Utc2Gps |
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% Other functions needed: LeapSeconds.m |
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%Author: Frank van Diggelen |
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%Open Source code for processing Android GNSS Measurements |
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%Algorithm for handling leap seconds: |
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% When a leap second happens, utc time stands still for one second, so |
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% gps seconds get further ahead, so we subtract leapSecs to move from gps time |
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% |
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% 1) convert gpsTime to time = [yyyy,mm,dd,hh,mm,ss] (with no leap seconds) |
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% 2) look up leap seconds for time: ls = LeapSeconds(time); |
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% This is (usually) the correct leap second value. Unless: |
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% If (utcTime=time) and (utcTime=time+ls) straddle a leap second |
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% then we need to add 1 to ls |
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% So, after step 2) ... |
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% 3) convert gpsTime-ls to timeMLs |
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% 4) look up leap seconds: ls1 = LeapSeconds(timeMLs); |
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% 5) if ls1~=ls, convert (gpsTime-ls1) to UTC Time |
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%% Check inputs |
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if size(gpsTime,2)~=2 |
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error('gpsTime must have two columns') |
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end |
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fctSeconds = gpsTime*[GpsConstants.WEEKSEC; 1]; |
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%fct at 2100/1/1 00:00:00, not counting leap seconds: |
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fct2100 = [6260, 432000]*[GpsConstants.WEEKSEC; 1]; |
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if any(fctSeconds<0) || any (fctSeconds >= fct2100) |
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error('gpsTime must be in this range: [0,0] <= gpsTime < [6260, 432000]'); |
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end |
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%% Finished checks |
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%from now on work with fct |
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%% Apply algorithm for handling leaps seconds |
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% 1) convert gpsTime to time = [yyyy,mm,dd,hh,mm,ss] (with no leap seconds) |
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time = Fct2Ymdhms(fctSeconds); |
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% 2) look up leap seconds for time: ls = LeapSeconds(time); |
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ls = LeapSeconds(time); |
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% 3) convert gpsTime-ls to timeMLs |
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timeMLs = Fct2Ymdhms(fctSeconds-ls); |
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% 4) look up leap seconds: ls1 = LeapSeconds(timeMLs); |
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ls1 = LeapSeconds(timeMLs); |
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% 5) if ls1~=ls, convert (gpsTime-ls1) to UTC Time |
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if all(ls1==ls) |
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utcTime = timeMLs; |
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else |
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utcTime = Fct2Ymdhms(fctSeconds-ls1); |
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end |
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% NOTE: |
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% Gps2Utc.m doesn't produce 23:59:60, at a leap second. |
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% Instead, as the leap second occurs, the Gps2Utc.m sequence of |
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% UTC hh:mm:ss is 23:59:59, 00:00:00, 00:00:00 |
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% and we keep it like that for code simplicity. |
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% Here are a sequence of UTC and GPS times around a leap second: |
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% formalUtcTimes = [1981 12 31 23 59 59; 1981 12 31 23 59 60; 1982 1 1 0 0 0]; |
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% gpsTimes = [103 431999; 103 432000; 103 432001]; |
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% >> Gps2Utc(gpsTimes) |
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% ans = |
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% 1981 12 31 23 59 59 |
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% 1982 1 1 0 0 0 |
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% 1982 1 1 0 0 0 |
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% If you want to change this you could check LeapSeconds.m to see if you're |
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% exactly on the addition of a leap second, and then change the UTC format |
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% to include the '60' seconds |
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end %end of function Gps2Utc |
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
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function time = Fct2Ymdhms(fctSeconds) |
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%Utility function for Gps2Utc |
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%Convert GPS full cycle time to [yyyy,mm,dd,hh,mm,ss.s] format |
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HOURSEC = 3600; MINSEC = 60; |
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monthDays=[31,28,31,30,31,30,31,31,30,31,30,31];%days each month (not leap year) |
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m=length(fctSeconds); |
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days = floor(fctSeconds / GpsConstants.DAYSEC) + 6;%days since 1980/1/1 |
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years=zeros(m,1)+1980; |
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%decrement days by a year at a time, until we have calculated the year: |
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leap=ones(m,1); %1980 was a leap year |
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while (any(days > (leap+365))) |
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I = find(days > (leap+365) ); |
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days(I) = days(I) - (leap(I) + 365); |
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years(I)=years(I)+1; |
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leap(I) = (rem(years(I),4) == 0); % leap = 1 on a leap year, 0 otherwise |
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% This works from 1901 till 2099, 2100 isn't a leap year (2000 is). |
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% Calculate the year, ie time(1) |
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end, |
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time=zeros(m,6);%initialize matrix |
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time(:,1)=years; |
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%decrement days by a month at a time, until we have calculated the month |
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% Calculate the month, ie time(:,2) |
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% Loop through m: |
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for i=1:m |
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month = 1; |
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if (rem(years(i),4) == 0) %This works from 1901 till 2099 |
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monthDays(2)=29; %Make February have 29 days in a leap year |
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else |
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monthDays(2)=28; |
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end |
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while (days(i) > monthDays(month)) |
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days(i) = days(i)-monthDays(month); |
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month = month+1; |
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end |
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time(i,2)=month; |
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end |
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time(:,3) = days; |
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sinceMidnightSeconds = rem(fctSeconds, GpsConstants.DAYSEC); |
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time(:,4) = fix(sinceMidnightSeconds/HOURSEC); |
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lastHourSeconds = rem(sinceMidnightSeconds, HOURSEC); |
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time(:,5) = fix(lastHourSeconds/MINSEC); |
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time(:,6) = rem(lastHourSeconds,MINSEC); |
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end %end of function Fct2Ymdhms |
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
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% Copyright 2016 Google Inc. |
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% |
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% Licensed under the Apache License, Version 2.0 (the "License"); |
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% you may not use this file except in compliance with the License. |
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% You may obtain a copy of the License at |
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% |
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% http://www.apache.org/licenses/LICENSE-2.0 |
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% |
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% Unless required by applicable law or agreed to in writing, software |
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% distributed under the License is distributed on an "AS IS" BASIS, |
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% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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% See the License for the specific language governing permissions and |
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% limitations under the License. |
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