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--[[
Sample plots using date / time formatting for axes
Copyright (C) 2009 Werner Smekal
This file is part of PLplot.
PLplot is free software you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published
by the Free Software Foundation either version 2 of the License, or
(at your option) any later version.
PLplot 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 Library General Public License for more details.
You should have received a copy of the GNU Library General Public License
along with PLplot if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
--]]
-- initialise Lua bindings for PLplot examples.
dofile("plplot_examples.lua")
-- Plot a model diurnal cycle of temperature
function plot1()
x = {}
y = {}
xerr1 = {}
xerr2 = {}
yerr1 = {}
yerr2 = {}
-- Data points every 10 minutes for 1 day
npts = 73
xmin = 0
xmax = 60*60*24 -- Number of seconds in a day
ymin = 10
ymax = 20
for i = 1, npts do
x[i] = xmax*((i-1)/npts)
y[i] = 15 - 5*math.cos(2*math.pi*((i-1)/npts))
-- Set x error bars to +/- 5 minute
xerr1[i] = x[i]-60*5
xerr2[i] = x[i]+60*5
-- Set y error bars to +/- 0.1 deg C
yerr1[i] = y[i]-0.1
yerr2[i] = y[i]+0.1
end
pl.adv(0)
-- Rescale major ticks marks by 0.5
pl.smaj(0, 0.5)
-- Rescale minor ticks and error bar marks by 0.5
pl.smin(0, 0.5)
pl.vsta()
pl.wind(xmin, xmax, ymin, ymax)
-- Draw a box with ticks spaced every 3 hour in X and 1 degree C in Y.
pl.col0(1)
-- Set time format to be hours:minutes
pl.timefmt("%H:%M")
pl.box("bcnstd", 3*60*60, 3, "bcnstv", 1, 5)
pl.col0(3)
pl.lab("Time (hours:mins)", "Temperature (degC)", "@frPLplot Example 29 - Daily temperature")
pl.col0(4)
pl.line(x, y)
pl.col0(2)
pl.errx(xerr1, xerr2, y)
pl.col0(3)
pl.erry(x, yerr1, yerr2)
-- Rescale major / minor tick marks back to default
pl.smin(0, 1)
pl.smaj(0, 1)
end
-- Plot the number of hours of daylight as a function of day for a year
function plot2()
x = {}
y = {}
-- Latitude for London
lat = 51.5
npts = 365
xmin = 0
xmax = npts*60*60*24
ymin = 0
ymax = 24
-- Formula for hours of daylight from
-- "A Model Comparison for Daylength as a Function of Latitude and
-- Day of the Year", 1995, Ecological Modelling, 80, pp 87-95.
for j = 1, npts do
x[j] = (j-1)*60*60*24
p = math.asin(0.39795*math.cos(0.2163108 + 2*math.atan(0.9671396*math.tan(0.00860*(j-1-186)))))
d = 24 - (24/math.pi)*
math.acos( (math.sin(0.8333*math.pi/180) + math.sin(lat*math.pi/180)*math.sin(p)) /
(math.cos(lat*math.pi/180)*math.cos(p)) )
y[j] = d
end
pl.col0(1)
-- Set time format to be abbreviated month name followed by day of month
pl.timefmt("%b %d")
pl.prec(1, 1)
pl.env(xmin, xmax, ymin, ymax, 0, 40)
pl.col0(3)
pl.lab("Date", "Hours of daylight", "@frPLplot Example 29 - Hours of daylight at 51.5N")
pl.col0(4)
pl.line(x, y)
pl.prec(0, 0)
end
function plot3()
x = {}
y = {}
tstart = 1133395200
npts = 62
xmin = tstart
xmax = xmin + npts*60*60*24
ymin = 0
ymax = 5
for i = 1, npts do
x[i] = xmin + (i-1)*60*60*24
y[i] = 1 + math.sin(2*math.pi*(i-1)/7) + math.exp(math.min(i-1,npts-i+1)/31)
end
pl.adv(0)
pl.vsta()
pl.wind(xmin, xmax, ymin, ymax)
pl.col0(1)
-- Set time format to be ISO 8601 standard YYYY-MM-DD. Note that this is
--equivalent to %f for C99 compliant implementations of strftime.
pl.timefmt("%Y-%m-%d")
-- Draw a box with ticks spaced every 14 days in X and 1 hour in Y.
pl.box("bcnstd", 14*24*60*60,14, "bcnstv", 1, 4)
pl.col0(3)
pl.lab("Date", "Hours of television watched", "@frPLplot Example 29 - Hours of television watched in Dec 2005 / Jan 2006")
pl.col0(4)
-- Rescale symbol size (used by plpoin) by 0.5
pl.ssym(0, 0.5)
pl.poin(x, y, 2)
pl.line(x, y)
end
function plot4()
-- TAI-UTC (seconds) as a function of time.
x = {}
y = {}
-- Continuous time unit is Besselian years from whatever epoch is
-- chosen below. Could change to seconds (or days) from the
-- epoch, but then would have to adjust xlabel_step below.
scale = 365.242198781
-- MJD epoch (see <https://en.wikipedia.org/wiki/Julian_day>).
-- This is only set for illustrative purposes, and is overwritten
-- below for the time-representation reasons given in the
-- discussion below.
epoch_year = 1858
epoch_month = 11
epoch_day = 17
epoch_hour = 0
epoch_min = 0
epoch_sec = 0.
-- To illustrate the time-representation issues of using the MJD
-- epoch, in 1985, MJD was roughly 46000 days which corresponds to
-- 4e9 seconds. Thus, for the -DPL_DOUBLE=ON case where PLFLT is
-- a double which can represent continuous time to roughly 16
-- decimal digits of precision the time-representation error is
-- roughly ~400 nanoseconds. Therefore the MJD epoch would be
-- acceptable for the plots below in the -DPL_DOUBLE=ON case.
-- However, that epoch is obviously not acceptable for the
-- -DPL_DOUBLE=OFF case where PLFLT is a float which can represent
-- continuous time to only ~7 decimal digits of precision
-- corresponding to a time representation error of 400 seconds (!)
-- in 1985. For this reason, we do not use the MJD epoch below
-- and instead choose the best epoch for each case to minimize
-- time-representation issues.
for kind = 0, 6 do
if kind == 0 then
-- Choose midpoint to maximize time-representation precision.
epoch_year = 1985
epoch_month = 0
epoch_day = 2
epoch_hour = 0
epoch_min = 0
epoch_sec = 0.
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
xmin = pl.ctime(1950, 0, 2, 0, 0, 0)
xmax = pl.ctime(2020, 0, 2, 0, 0, 0)
npts = 70*12 + 1
ymin = 0
ymax = 36
time_format = "%Y%"
if_TAI_time_format = 1
title_suffix = "from 1950 to 2020"
xtitle = "Year"
xlabel_step = 10
end
if kind==1 or kind==2 then
-- Choose midpoint to maximize time-representation precision.
epoch_year = 1961
epoch_month = 7
epoch_day = 1
epoch_hour = 0
epoch_min = 0
epoch_sec = 1.64757
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
xmin = pl.ctime(1961, 7, 1, 0, 0, 1.64757-0.20)
xmax = pl.ctime(1961, 7, 1, 0, 0, 1.64757+0.20)
npts = 1001
ymin = 1.625
ymax = 1.725
time_format = "%S%2%"
title_suffix = "near 1961-08-01 (TAI)"
xlabel_step = 0.05/(scale*86400)
if kind==1 then
if_TAI_time_format = 1
xtitle = "Seconds (TAI)"
else
if_TAI_time_format = 0
xtitle = "Seconds (TAI) labelled with corresponding UTC"
end
end
if kind==3 or kind==4 then
-- Choose midpoint to maximize time-representation precision.
epoch_year = 1963
epoch_month = 10
epoch_day = 1
epoch_hour = 0
epoch_min = 0
epoch_sec = 2.6972788
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
xmin = pl.ctime(1963, 10, 1, 0, 0, 2.6972788-0.20)
xmax = pl.ctime(1963, 10, 1, 0, 0, 2.6972788+0.20)
npts = 1001
ymin = 2.55
ymax = 2.75
time_format = "%S%2%"
title_suffix = "near 1963-11-01 (TAI)"
xlabel_step = 0.05/(scale*86400)
if kind==3 then
if_TAI_time_format = 1
xtitle = "Seconds (TAI)"
else
if_TAI_time_format = 0
xtitle = "Seconds (TAI) labelled with corresponding UTC"
end
end
if kind==5 or kind==6 then
-- Choose midpoint to maximize time-representation precision.
epoch_year = 2009
epoch_month = 0
epoch_day = 1
epoch_hour = 0
epoch_min = 0
epoch_sec = 34.
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
xmin = pl.ctime(2009, 0, 1, 0, 0, 34-5)
xmax = pl.ctime(2009, 0, 1, 0, 0, 34+5)
npts = 1001
ymin = 32.5
ymax = 34.5
time_format = "%S%2%"
title_suffix = "near 2009-01-01 (TAI)"
xlabel_step = 1/(scale*86400)
if kind==5 then
if_TAI_time_format = 1
xtitle = "Seconds (TAI)"
else
if_TAI_time_format = 0
xtitle = "Seconds (TAI) labelled with corresponding UTC"
end
end
for i = 1, npts do
x[i] = xmin + (i-1)*(xmax-xmin)/(npts-1)
tai = x[i]
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
tai_year, tai_month, tai_day, tai_hour, tai_min, tai_sec = pl.btime(tai)
-- Calculate residual using tai as the epoch to nearly maximize time-representation precision.
pl.configtime(scale, 0., 0., 0, 1, tai_year, tai_month, tai_day, tai_hour, tai_min, tai_sec)
-- Calculate continuous tai with new epoch.
tai = pl.ctime(tai_year, tai_month, tai_day, tai_hour, tai_min, tai_sec)
-- Calculate broken-down utc (with leap seconds inserted) from continuous tai with new epoch.
pl.configtime(scale, 0., 0., 2, 1, tai_year, tai_month, tai_day, tai_hour, tai_min, tai_sec)
utc_year, utc_month, utc_day, utc_hour, utc_min, utc_sec = pl.btime(tai)
-- Calculate continuous utc from broken-down utc using same epoch as for the continuous tai.
pl.configtime(scale, 0., 0., 0, 1, tai_year, tai_month, tai_day, tai_hour, tai_min, tai_sec)
utc = pl.ctime(utc_year, utc_month, utc_day, utc_hour, utc_min, utc_sec)
-- Convert residuals to seconds.
y[i]=(tai-utc)*scale*86400.
end
pl.adv(0)
pl.vsta()
pl.wind(xmin, xmax, ymin, ymax)
pl.col0(1)
if if_TAI_time_format ~= 0 then
pl.configtime(scale, 0., 0., 0, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
else
pl.configtime(scale, 0., 0., 2, 1, epoch_year, epoch_month, epoch_day, epoch_hour, epoch_min, epoch_sec)
end
pl.timefmt(time_format)
pl.box("bcnstd", xlabel_step, 0, "bcnstv", 0., 0)
pl.col0(3)
title = "@frPLplot Example 29 - TAI-UTC " .. title_suffix
pl.lab(xtitle, "TAI-UTC (sec)", title)
pl.col0(4)
pl.line(x, y)
end
end
----------------------------------------------------------------------------
-- main
--
-- Draws several plots which demonstrate the use of date / time formats for
-- the axis labels.
-- Time formatting is done using the system strftime routine. See the
-- documentation of this for full details of the available formats.
--
-- 1) Plotting temperature over a day (using hours / minutes)
-- 2) Plotting
--
-- Note: Times are stored as seconds since the epoch (usually 1st Jan 1970).
--
----------------------------------------------------------------------------
-- Parse command line arguments
pl.parseopts(arg, pl.PL_PARSE_FULL)
-- Initialize plplot
pl.init()
-- Change the escape character to a '@' instead of the default '#'
pl.sesc('@')
plot1()
plot2()
plot3()
plot4()
-- Don't forget to call plend() to finish off!
pl.plend()