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/* Copyright (C) 2006 Imperial College London and others.
Please see the AUTHORS file in the main source directory for a full list
of copyright holders.
Dr Gerard Gorman
Applied Modelling and Computation Group
Department of Earth Science and Engineering
Imperial College London
g.gorman@imperial.ac.uk
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation,
version 2.1 of the License.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
USA
*/
#ifndef CALENDAR_H
#define CALENDAR_H
#include "confdefs.h"
#include "c++debug.h"
#include <cassert>
#include <iostream>
#include <string>
#ifdef HAVE_LIBUDUNITS
extern "C"{
#include <udunits.h>
// The udunits people forgot to include this in their header file
// int utIsInit();
extern int utIsInit PROTO(());
}
#endif
#include <stdlib.h>
/* Adapted from the NetCDF CF-convention
In order to calculate a new date and time given a base date, base
time and a time increment one must know what calendar to use. For
this purpose NetCDF CF-conventions recommend that the calendar be
specified by the NetCDF attribute calendar which is assigned to
the time coordinate variable. The values currently defined for
calendar are:
gregorian or standard: Mixed Gregorian/Julian calendar as defined
by Udunits. This is the default.
proleptic_gregorian: A Gregorian calendar extended to dates
before 1582-10-15. That is, a year is a leap year if either (i)
it is divisible by 4 but not by 100 or (ii) it is divisible by
400.
noleap or 365_day: Gregorian calendar without leap years, i.e.,
all years are 365 days long.
all_leap or 366_day: Gregorian calendar with every year being a
leap year, i.e., all years are 366 days long.
360_day: All years are 360 days divided into 30 day months.
julian: Julian calendar.
none: No calendar.
The calendar attribute may be set to none in climate experiments
that simulate a fixed time of year. The time of year is indicated
by the date in the reference time of the units attribute. The
time coordinate that might apply in a perpetual July experiment
are given in the following example.
Example 4.5. Perpetual time axis
variables:
double time(time) ;
time:long_name = "time" ;
time:units = "days since 1-7-15 0:0:0" ;
time:calendar = "none" ;
data:
time = 0., 1., 2., ...;
Here, all days simulate the conditions of 15th July, so it does
not make sense to give them different dates. The time coordinates
are interpreted as 0, 1, 2, etc. days since the start of the
experiment.
If none of the calendars defined above applies (e.g., calendars
appropriate to a different paleoclimate era), a non-standard
calendar can be defined. The lengths of each month are explicitly
defined with the month_lengths attribute of the time axis:
month_lengths: A vector of size 12, specifying the number of days
in the months from January to December (in a non-leap year).
leap_year: If leap years are included, then two other attributes
of the time axis should also be defined:
leap_month: An example of a leap year. It is assumed that all
years that differ from this year by a multiple of four are also
leap years. If this attribute is absent, it is assumed there are
no leap years.
A value in the range 1-12, specifying which month is lengthened
by a day in leap years (1=January). If this attribute is not
present, February (2) is assumed. This attribute is ignored if
leap_year is not specified.
The calendar attribute is not required when a non-standard
calendar is being used. It is sufficient to define the calendar
using the month_lengths attribute, along with leap_year, and
leap_month as appropriate. However, the calendar attribute is
allowed to take non-standard values and in that case defining the
non-standard calendar using the appropriate attributes is
required.
Example 4.6. Paleoclimate time axis
double time(time) ;
time:long_name = "time" ;
time:units = "days since 1-1-1 0:0:0" ;
time:calendar = "126 kyr B.P." ;
time:month_lengths = 34, 31, 32, 30, 29, 27, 28, 28, 28, 32, 32, 34 ;
The mixed Gregorian/Julian calendar used by Udunits is explained
in the following excerpt from the udunits(3) man page:
The udunits(3) package uses a mixed Gregorian/Julian calen-
dar system. Dates prior to 1582-10-15 are assumed to use
the Julian calendar, which was introduced by Julius Caesar
in 46 BCE and is based on a year that is exactly 365.25 days
long. Dates on and after 1582-10-15 are assumed to use the
Gregorian calendar, which was introduced on that date and is
based on a year that is exactly 365.2425 days long. (A year
is actually approximately 365.242198781 days long.) Seem-
ingly strange behavior of the udunits(3) package can result
if a user-given time interval includes the changeover date.
For example, utCalendar() and utInvCalendar() can be used to
show that 1582-10-15 *preceded* 1582-10-14 by 9 days.
Due to problems caused by the discontinuity in the default mixed
Gregorian/Julian calendar, we strongly recommend that this
calendar should only be used when the time coordinate does not
cross the discontinuity. For time coordinates that do cross the
discontinuity the proleptic_gregorian calendar should be used
instead.
*/
class Calendar{
// This class aims to implement calander tools to conform to NetCDF
// Climate and Forecast (CF) Metadata Conventions.
//
// http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-1.0.html
public:
Calendar();
Calendar(const Calendar&);
const Calendar& operator=(const Calendar &);
~Calendar();
int Convert(double from_value, double& to_value);
int SetTransformation(std::string from_unit, std::string to_unit, std::string calendar);
private:
#ifdef HAVE_LIBUDUNITS
utUnit from_unit, to_unit;
#endif
bool have_units;
double slope, intercept;
std::string calendar;
};
#endif
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