x 轴上时间戳的格式

2024-01-05

我正在尝试格式化天气数据图中的 x 轴。我对 y 轴很满意，但我所有将 x 轴变成合适的、人类可读格式的尝试到目前为止都不起作用。因此，经过几个小时的尝试和错误，我希望对您有所帮助。

我想要实现的目标

最后，我希望每 30 分钟有一个刻度线，每小时有一条垂直的点状网格线，其下方的时间写为 HH:MM，另外还写有每晚 00:00 的日期。像这样的东西（注意，前面的 ASCII 艺术很糟糕！）：

     :         :         :
     :         :         :
     :         :         :
     :         :         :
     :         :         :
|====|====|====|====|====|====|====
   23:00     00:00     01:00
            09JAN18

所有时间均采用 UTC，这将是最终的豪华版本。但我的问题很早就开始了。

我的代码片段

一开始我试图将其变成可读的格式。我想出了

locator = mdates.AutoDateLocator()
plt.gca().xaxis.set_major_locator(locator)
plt.gca().xaxis.set_major_formatter(mdates.AutoDateFormatter(locator))

希望我能摆脱exp

结果

输出并不完全是我所希望的：

pi@raspi3b:~/wx-logging $ python plot.py
[( 15.94,  57.86,  992.65,  1019.99, 1515460740)
 ( 15.96,  57.8 ,  992.65,  1019.99, 1515460745)
 ( 15.99,  57.79,  992.68,  1020.02, 1515460750) ...,
 ( 13.25,  55.7 ,  990.16,  1017.43, 1515496060)
 ( 13.31,  56.  ,  990.14,  1017.41, 1515496065)
 ( 13.34,  56.32,  990.13,  1017.4 , 1515496070)]
Traceback (most recent call last):
  File "plot.py", line 123, in <module>
    plt.savefig("plot.png", dpi=150)
  File "/usr/lib/python2.7/dist-packages/matplotlib/pyplot.py", line 697, in savefig
    res = fig.savefig(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/figure.py", line 1572, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backend_bases.py", line 2244, in print_figure
    **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 545, in print_png
    FigureCanvasAgg.draw(self)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_agg.py", line 464, in draw
    self.figure.draw(self.renderer)
  File "/usr/lib/python2.7/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/figure.py", line 1143, in draw
    renderer, self, dsu, self.suppressComposite)
  File "/usr/lib/python2.7/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axes_grid1/parasite_axes.py", line 295, in draw
    self._get_base_axes_attr("draw")(self, renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axislines.py", line 778, in draw
    super(Axes, self).draw(renderer, inframe)
  File "/usr/lib/python2.7/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/matplotlib/axes/_base.py", line 2409, in draw
    mimage._draw_list_compositing_images(renderer, self, dsu)
  File "/usr/lib/python2.7/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axis_artist.py", line 915, in draw
    gl = self._grid_helper.get_gridlines(self._which, self._axis)
  File "/usr/lib/python2.7/dist-packages/mpl_toolkits/axisartist/axislines.py", line 546, in get_gridlines
    locs.extend(self.axes.xaxis.major.locator())
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 983, in __call__
    self.refresh()
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 1003, in refresh
    dmin, dmax = self.viewlim_to_dt()
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 760, in viewlim_to_dt
    return num2date(vmin, self.tz), num2date(vmax, self.tz)
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 401, in num2date
    return _from_ordinalf(x, tz)
  File "/usr/lib/python2.7/dist-packages/matplotlib/dates.py", line 254, in _from_ordinalf
    dt = datetime.datetime.fromordinal(ix).replace(tzinfo=UTC)
ValueError: year is out of range
pi@raspi3b:~/wx-logging $

不太有希望。我不明白为什么它说ValueError: year is out of range因为它是一个 Unix 纪元时间戳。

我究竟做错了什么？我怎样才能达到上述预期的结果？我真的很感激能朝正确的方向推动。感谢您的帮助！

一切顺利，克里斯

完整的脚本

到目前为止，我为您提供了一些完整的脚本的背景信息。

#!/usr/bin/python
# -*- coding: utf-8 -*-

import matplotlib
matplotlib.use('AGG')
from mpl_toolkits.axes_grid1 import host_subplot
import mpl_toolkits.axisartist as aa
import matplotlib.pyplot as plt
import matplotlib.dates as mdates
from matplotlib.ticker import FuncFormatter
import numpy as np
from numpy import vectorize
import datetime
import shutil
import math

# Dewpoint calculation
def dewpoint(tempC, rlHum):

    r  = 8314.3
    mw = 18.016

    if tempC >= 0:
        a = 7.5
        b = 237.3
    # over water:
    # elif tempC < 0:
    #     a = 7.6
    #     b = 240.7
    #
    # over ice:
    elif tempC < 0:
        a = 9.5
        b = 265.5

    saettDampfDruck = 6.1078 * 10**((a*tempC)/(b+tempC))
    dampfDruck = rlHum / 100.0 * saettDampfDruck
    v = math.log10(dampfDruck/6.1078)
    dewpC = b*v/(a-v)

    return dewpC

# translate cm into inches
def cm2inch(*tupl):
    inch = 2.54
    if isinstance(tupl[0], tuple):
        return tuple(i/inch for i in tupl[0])
    else:
        return tuple(i/inch for i in tupl)

vdewpoint = vectorize(dewpoint)

convertDate = lambda x: datetime.datetime.utcfromtimestamp(x)

data = np.genfromtxt('/home/pi/wx-logging/wx-log2.txt', 
                    delimiter=';', 
                    usecols=(1, 2, 3, 5, 6), 
                    names=['temp', 'humidity', 'press', 'slp', 'time'], 
                    converters={'6': convertDate}, 
                    dtype='float, float, float, float, int')

print data

plt.figure(figsize=cm2inch(29.7, 21))

host = host_subplot(111, axes_class=aa.Axes)
plt.subplots_adjust(right=0.75)
par1 = host.twinx()
par2 = host.twinx()

offset = 70 # offset of detached axis
new_fixed_axis = par2.get_grid_helper().new_fixed_axis
par2.axis["right"] = par2.get_grid_helper().new_fixed_axis(loc="right", 
                                                            axes=par2, 
                                                            offset=(offset, 0))

par1.axis["right"].toggle(all=True)
par2.axis["right"].toggle(all=True)

host.set_title("Weather Station")
host.set_xlabel("Time")
host.set_ylabel("Temperature & Dewpoint [" + u'\u00b0'+ "C]")
par1.set_ylabel("Sealevel Pressure [hPa]")
par2.set_ylabel("relative Humidity [%]")

host.set_ylim([-20, 40]) # temperature range -20C ... +40C
par1.set_ylim([980, 1040]) # slp range 980hPa ... 1040hPa
par2.set_ylim([0, 100]) # percent


p1, = host.plot(data['time'],
                data['temp'],
                label="Temperature",
                color="red",
                linewidth=2)
p2, = host.plot(data['time'],
                vdewpoint(data['temp'],
                data['humidity']),
                label="Dewpoint",
                color="salmon",
                linewidth=0.75)
p3, = par1.plot(data['time'],
                data['slp'],
                label="Sealevel Pressure",
                color="blue",
                linewidth=0.75)
p4, = par2.plot(data['time'],
                data['humidity'],
                label="rel. Humidity",
                color="grey",
                linewidth=0.5)

locator = mdates.AutoDateLocator()
plt.gca().xaxis.set_major_locator(locator)
plt.gca().xaxis.set_major_formatter(mdates.AutoDateFormatter(locator))


plt.legend(bbox_to_anchor=(0.05, 0.05), 
           loc=3,
           ncol=2, 
           borderaxespad=0.)

plt.savefig("plot.png", dpi=150)

shutil.copyfile('/home/pi/wx-logging/plot.png', '/var/www/html/plot.png')

EDIT1:您可以下载wx-log2.txt http://kristofkoch.de/stackexchange/wx-log2.txt(~58KB) 包含用于试验脚本的示例数据。蒂亚戈正确建议

您的代码有一些问题。首先，使用引号中的列converters={'6':意味着永远不会应用转换函数。使用不带引号的列号：

converters={6: convertDate},

另一个问题是您需要从字符串转换为整数，否则您的日期时间转换将不起作用：

convertDate = lambda x: datetime.datetime.utcfromtimestamp(int(x))

最后，你的数据类型time字段必须是numpy.datatype64（并以微秒为单位指定，因为这就是utcfromtimestamp返回）。分配数据类型的正确方法np.genfromtxt调用如下：

data = np.genfromtxt('wx-log2.txt',  
                     delimiter=';',
                     converters={6: convertDate},
                     usecols=(1,2,3,5,6), 
                     dtype=[('temp', 'f'), ('humidity', 'f'), ('press', 'f'), 
                            ('slp', 'f'), ('time', 'datetime64[us]')])

通过以上内容，您应该如何使用以下格式的时间：plt.plot_date可以理解。

对于日期格式，您可以通过将小刻度线标签设置为与您试图实现的类似的方式HH:MM和主要是一年中的一天，但我不知道如何每 30 分钟另外添加未标记的刻度线。

这是一个简单的示例，它具有适当的时间数组并以与您想要的格式类似的格式绘制。为简单起见，每 4 小时只写一次刻度线，但您可以更改它。

import numpy as np
import matplotlib.dates as dates
import matplotlib.pyplot as plt 

fig, ax = plt.subplots()
idx = pd.date_range('2018-01-07', '2018-01-09', freq='10min')
# generate a time range series with 10 min intervals
idx = np.arange('2018-01-07T00', '2018-01-09T02', 10, dtype='datetime64[m]')
# some random data
y = np.sin(np.arange(idx.shape[0]) / 0.01)

ax.plot_date(idx, y, '-')

ax.xaxis.set_minor_locator(dates.HourLocator(interval=4))   # every 4 hours
ax.xaxis.set_minor_formatter(dates.DateFormatter('%H:%M'))  # hours and minutes
ax.xaxis.set_major_locator(dates.DayLocator(interval=1))    # every day
ax.xaxis.set_major_formatter(dates.DateFormatter('\n%d-%m-%Y'))

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