function [gregorian_base, rescale_serial_rel, serial_base_jd, serial_base] = parsetnc(time_units_str)% PARSETNC: parses the COARDS string that specifies time units%%function [gregorian_base, rescale_serial_rel, serial_base_jd, ...%          serial_base] = parsetnc(time_units_str)%%        INPUT:% time_units_str: The string stored as the units attribute of the time%    variable in a COARDS standard netcdf file. It is like:%    'seconds since 1992-10-8 15:15:42.5 -6:00'%%        OUTPUT:% gregorian_base: a 6-vector giving the year, month, day, hour, minute,%    second of the base time as specified in time_units_str. This is in UT.% rescale_serial_rel: number used to convert the time vector in the netcdf%    file to days. For example if time_units_str is%    'seconds since 1992-10-8 15:15:42.5 -6:00' then rescale_serial_rel is%    1/(24*60*60).% serial_base_jd: the Julian day number of the base time, in UT, as%    determined by get_julian_day. Thus gregorian_base =%    get_calendar_date(serial_base_jd).% serial_base: the serial time of the base time, in UT, as determined by%    matlab's datenum function. Thus gregorian_base = datevec(serial_base).%    serial_base will be problematic for times before October 15 1582, when%    the Gregorian calendar was adopted, since datenum is proleptic gregorian%    and so not what you might expect.%%        Notes:% In a COARDS standard netcdf file time is specified relative to a standard% time by the time variable having a units attribute of the form:%      'seconds since 1992-10-8 15:15:42.5 -6:00'% This indicates seconds since October 8th, 1992 at 3 hours, 15% minutes and 42.5 seconds in the afternoon in the time zone% which is six hours to the west of Coordinated Universal Time% (i.e. Mountain Daylight Time). The time zone specification can% also be written without a colon using one or two-digits% (indicating hours) or three or four digits (indicating hours% and minutes).  Instead of 'seconds' the string may contain 'minutes',% 'hours', 'days' and 'weeks' and all of these may be singular or plural% and have capital first letters.  I also allow the letters 'UTC' or% 'UT' at the end of the string, but these are ignored.%% All calculations are done using the functions get_calendar_date and% get_julian_day which know about both the Julian and Gregorian calendars and% so work back to julian day 0 in the year -4712.% This function calls: get_calendar_date.m, get_julian_day.m% This function is called by: get_serial_time.m, timenc.m% $Id: parsetnc.m Mon, 03 Jul 2006 17:16:40 $% Copyright J. V. Mansbridge, CSIRO, Thursday September 16 11:12:35 EST 1999% Note 1) I had trouble using strtok with ':' and '-' and so I converted%         the first 2 instances of each of them to spaces.  This leaves%         the correction to Universal time (if there is one) untouched.fm = find(time_units_str == '-');fc = find(time_units_str == ':');str = time_units_str;if length(fm) >= 2  str(fm(1:2)) = ' ';else  error('The year-month-day string is wrongly specified in the base date')endif length(fc) == 1  str(fc(1)) = ' ';elseif length(fc) >= 2  str(fc(1:2)) = ' ';endstr = char(str);%Convert the time vector to serial days since the base time.[str, remainder] = strtok(str);if ( strcmp('week', str) | strcmp('weeks', str) | ...      strcmp('Week', str) | strcmp('week', str) )  rescale_serial_rel = 7;elseif ( strcmp('day', str) | strcmp('days', str) | ...      strcmp('Day', str) | strcmp('day', str) )  rescale_serial_rel = 1;elseif ( strcmp('hour', str) | strcmp('hours', str) | ...      strcmp('Hour', str) | strcmp('Hours', str) )  rescale_serial_rel = 1/24;elseif ( strcmp('minute', str) | strcmp('minutes', str) | ...      strcmp('Minute', str) | strcmp('Minutes', str) )  rescale_serial_rel = 1/(24*60);elseif ( strcmp('second', str) | strcmp('seconds', str) | ...      strcmp('Second', str) | strcmp('Seconds', str) )  rescale_serial_rel = 1/(24*60*60);else  error(['bad time baseline string = ' time_units_str ])end%Find the serial base time (initially without paying attention to any%reference to Universal time).[str, remainder] = strtok(remainder);[str, remainder] = strtok(remainder);if isempty(str)  error('The base time has no string for the year')endyear_base = str2num(str);[str, remainder] = strtok(remainder);if isempty(str)  error('The base time has no string for the month')endmonth_base = str2num(str);[str, remainder] = strtok(remainder);if isempty(str)  error('The base time has no string for the day')endday_base = str2num(str);[str, remainder] = strtok(remainder);if isempty(str)  disp('The base time has no string for the hour, assume hour = min = sec = 0')  hour_base = 0;  minute_base = 0;  second_base = 0;else  hour_base = str2num(str);  [str, remainder] = strtok(remainder);  if isempty(str)    disp('The base time has no string for the minute, assume min = sec = 0')    minute_base = 0;    second_base = 0;  else    minute_base = str2num(str);    [str, remainder] = strtok(remainder);    if isempty(str)      disp('The base time has no string for the second, assume sec = 0')      second_base = 0;    else      second_base = str2num(str);    end  endendgregorian_base = [year_base month_base day_base hour_base ...        minute_base second_base];serial_base = datenum(year_base, month_base, day_base, hour_base, ...    minute_base, second_base);serial_base_jd = get_julian_day(gregorian_base);% Strip off some strings whose meaning we understand and also any trailing% blanks from remainder.string_list = {'UTC', 'utc', 'UT', 'ut'};for ii = 1:length(string_list)  xx = findstr(remainder, string_list{ii});  if ~isempty(xx)    remainder = remainder(1:(xx-1));    break  endendremainder = deblank(remainder);% If the remainder of the string is not empty (or filled with blanks)% then we assume that there is information about the conversion to% Universal time.  This is parsed and serial_base and gregorian_base are% then modified appropriately.if ~isempty(remainder)  % Find the number of hours and minutes that the time is offset from  % Coordinated Universal Time.    fc = find(remainder == ':');  if length(fc) == 0    intxx = str2num(remainder);    if ( (-99 < intxx) & ( intxx < 99) )      hour_extra = intxx;      min_extra = 0;    elseif ( (-9999 < intxx) & ( intxx < 9999) )      hour_extra = fix(0.01*intxx);      min_extra = intxx - 100*hour_extra;    else      error(['1:Universal time offset is faulty in ' time_units_str])    end  elseif length(fc) == 1    [str, remainder] = strtok(remainder, ':');    hour_extra = str2num(str);    [str, remainder] = strtok(remainder, ':');    min_extra = sign(hour_extra)*str2num(str);  else    error(['2:Universal time offset is faulty in ' time_units_str])  end   % Error checks    if ((hour_extra < -12) | (hour_extra > 12))    error(['3:Universal time offset is faulty in ' time_units_str])  end  if ((min_extra < -59) | (min_extra > 59))    error(['4:Universal time offset is faulty in ' time_units_str])  end  % Convert the Universal time correction to days.    time_extra = (hour_extra + min_extra/60)/24;  % Correct serial_base from the local time, as specified in the early  % part of the string, to Universal time.  Thus in the example  % 'seconds since 1992-10-8 15:15:42.5 -6:00' we will have  % time_extra = -6/24 days and this value must be subtracted from  % serial_base.  serial_base = serial_base - time_extra;  serial_base_jd = serial_base_jd - time_extra;  gregorian_base = get_calendar_date(serial_base_jd);end