#!/usr/bin/env python
# pywws - Python software for USB Wireless Weather Stations
# http://github.com/jim-easterbrook/pywws
# Copyright (C) 2008-16 pywws contributors
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
# This program 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 General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
"""conversions.py - a set of functions to convert pywws native units
(Centigrade, mm, m/s, hPa) to other popular units
"""
__docformat__ = "restructuredtext en"
import math
# rename imports to prevent them being imported when
# doing 'from pywws.conversions import *'
from pywws import Localisation as _Localisation
from pywws.Process import WindFilter as _WindFilter
[docs]def illuminance_wm2(lux):
"Approximate conversion of illuminance in lux to solar radiation in W/m2"
if lux is None:
return None
return lux * 0.005
[docs]def pressure_inhg(hPa):
"Convert pressure from hectopascals/millibar to inches of mercury"
if hPa is None:
return None
return hPa / 33.86389
[docs]def pressure_trend_text(trend):
"""Convert pressure trend to a string, as used by the UK met
office.
"""
_ = _Localisation.translation.ugettext
if trend > 6.0:
return _('rising very rapidly')
elif trend > 3.5:
return _('rising quickly')
elif trend > 1.5:
return _('rising')
elif trend >= 0.1:
return _('rising slowly')
elif trend < -6.0:
return _('falling very rapidly')
elif trend < -3.5:
return _('falling quickly')
elif trend < -1.5:
return _('falling')
elif trend <= -0.1:
return _('falling slowly')
return _('steady')
[docs]def rain_inch(mm):
"Convert rainfall from millimetres to inches"
if mm is None:
return None
return mm / 25.4
[docs]def temp_f(c):
"Convert temperature from Celsius to Fahrenheit"
if c is None:
return None
return (c * 9.0 / 5.0) + 32.0
[docs]def winddir_average(data, threshold, min_count, decay=1.0):
"""Compute average wind direction (in degrees) for a slice of data.
The wind speed and direction of each data item is converted to a
vector before averaging, so the result reflects the dominant wind
direction during the time period covered by the data.
Setting the ``decay`` parameter converts the filter from a simple
averager to one where the most recent sample carries the highest
weight, and earlier samples have a lower weight according to how
long ago they were.
This process is an approximation of "exponential smoothing". See
`Wikipedia <http://en.wikipedia.org/wiki/Exponential_smoothing>`_
for a detailed discussion.
The parameter ``decay`` corresponds to the value ``(1 - alpha)``
in the Wikipedia description. Because the weather data being
smoothed may not be at regular intervals this parameter is the
decay over 5 minutes. Weather data at other intervals will have
its weight scaled accordingly.
:note: The return value is in degrees, not the 0..15 range used
elsewhere in pywws.
:param data: a slice of pywws raw/calib or hourly data.
:type data: pywws.DataStore.core_store
:param threshold: minimum average windspeed for there to be a
valid wind direction.
:type threshold: float
:param min_count: minimum number of data items for there to be a
valid wind direction.
:type min_count: int
:param decay: filter coefficient decay rate.
:type decay: float
:rtype: float
"""
wind_filter = _WindFilter()
count = 0
for item in data:
wind_filter.add(item)
if item['wind_dir'] is not None:
count += 1
if count < min_count:
return None
speed, direction = wind_filter.result()
if speed is None or speed < threshold:
return None
return direction * 22.5
[docs]def winddir_degrees(pts):
"Convert wind direction from 0..15 to degrees"
if pts is None:
return None
return pts * 22.5
_winddir_text_array = None
[docs]def winddir_text(pts):
"Convert wind direction from 0..15 to compass point text"
global _winddir_text_array
if pts is None:
return None
if not isinstance(pts, int):
pts = int(pts + 0.5) % 16
if not _winddir_text_array:
_ = _Localisation.translation.ugettext
_winddir_text_array = (
_('N'), _('NNE'), _('NE'), _('ENE'),
_('E'), _('ESE'), _('SE'), _('SSE'),
_('S'), _('SSW'), _('SW'), _('WSW'),
_('W'), _('WNW'), _('NW'), _('NNW'),
)
return _winddir_text_array[pts]
[docs]def wind_kmph(ms):
"Convert wind from metres per second to kilometres per hour"
if ms is None:
return None
return ms * 3.6
[docs]def wind_mph(ms):
"Convert wind from metres per second to miles per hour"
if ms is None:
return None
return ms * 3.6 / 1.609344
[docs]def wind_kn(ms):
"Convert wind from metres per second to knots"
if ms is None:
return None
return ms * 3.6 / 1.852
_bft_threshold = (
0.3, 1.5, 3.4, 5.4, 7.9, 10.7, 13.8, 17.1, 20.7, 24.4, 28.4, 32.6)
[docs]def wind_bft(ms):
"Convert wind from metres per second to Beaufort scale"
if ms is None:
return None
for bft in range(len(_bft_threshold)):
if ms < _bft_threshold[bft]:
return bft
return len(_bft_threshold)
[docs]def dew_point(temp, hum):
"""Compute dew point, using formula from
http://en.wikipedia.org/wiki/Dew_point.
"""
if temp is None or hum is None:
return None
a = 17.27
b = 237.7
gamma = ((a * temp) / (b + temp)) + math.log(float(hum) / 100.0)
return (b * gamma) / (a - gamma)
[docs]def cadhumidex(temp, humidity):
"Calculate Humidity Index as per Canadian Weather Standards"
if temp is None or humidity is None:
return None
# Formulas are adapted to not use e^(...) with no appreciable
# change in accuracy (0.0227%)
saturation_pressure = (6.112 * (10.0**(7.5 * temp / (237.7 + temp))) *
float(humidity) / 100.0)
return temp + (0.555 * (saturation_pressure - 10.0))
[docs]def usaheatindex(temp, humidity, dew):
"""Calculate Heat Index as per USA National Weather Service Standards
See http://en.wikipedia.org/wiki/Heat_index, formula 1. The
formula is not valid for T < 26.7C, Dew Point < 12C, or RH < 40%
"""
if temp is None or humidity is None:
return None
if temp < 26.7 or humidity < 40 or dew < 12.0:
return temp
T = (temp * 1.8) + 32.0
R = humidity
c_1 = -42.379
c_2 = 2.04901523
c_3 = 10.14333127
c_4 = -0.22475541
c_5 = -0.00683783
c_6 = -0.05481717
c_7 = 0.00122874
c_8 = 0.00085282
c_9 = -0.00000199
return ((c_1 + (c_2 * T) + (c_3 * R) + (c_4 * T * R) + (c_5 * (T**2)) +
(c_6 * (R**2)) + (c_7 * (T**2) * R) + (c_8 * T * (R**2)) +
(c_9 * (T**2) * (R**2))) - 32.0) / 1.8
[docs]def wind_chill(temp, wind):
"""Compute wind chill, using formula from
http://en.wikipedia.org/wiki/wind_chill
"""
if temp is None or wind is None:
return None
wind_kph = wind * 3.6
if wind_kph <= 4.8 or temp > 10.0:
return temp
return min(13.12 + (temp * 0.6215) +
(((0.3965 * temp) - 11.37) * (wind_kph ** 0.16)),
temp)
[docs]def apparent_temp(temp, rh, wind):
"""Compute apparent temperature (real feel), using formula from
http://www.bom.gov.au/info/thermal_stress/
"""
if temp is None or rh is None or wind is None:
return None
vap_press = (float(rh) / 100.0) * 6.105 * math.exp(
17.27 * temp / (237.7 + temp))
return temp + (0.33 * vap_press) - (0.70 * wind) - 4.00
[docs]def cloud_base(temp, hum):
"""Calculate cumulus cloud base in metres, using formula from
https://en.wikipedia.org/wiki/Cloud_base or
https://de.wikipedia.org/wiki/Kondensationsniveau#Konvektionskondensationsniveau
"""
if temp is None or hum is None:
return None
dew_pt = dew_point(temp, hum)
spread = float(temp) - dew_pt
return spread * 125.0
[docs]def cloud_ft(m):
"Convert cloud base from metres to feet."
if m is None:
return None
return float(m) * 3.28084
def _main(argv=None):
global _winddir_text_array
# run some simple tests
print('Wind speed:')
print('%6s %8s %8s %8s %6s' % ('m/s', 'km/h', 'mph', 'knots', 'bft'))
for ms in (0, 1, 2, 4, 6, 9, 12, 15, 18, 22, 26, 30, 34):
print('%6g %8.3f %8.3f %8.3f %6d' % (
ms, wind_kmph(ms), wind_mph(ms), wind_kn(ms), wind_bft(ms)))
print('Wind direction:')
for pts in range(16):
print(winddir_text(pts), end=' ')
print()
print('Wind direction, in Swedish:')
_Localisation.SetTranslation('sv')
_winddir_text_array = None
for pts in range(16):
print(winddir_text(pts), end=' ')
print()
print('Cloud base in m and ft:')
for hum in range(25, 75, 5):
print("%8.3f m / %8.3f ft" % (cloud_base(15.0, hum), cloud_ft(cloud_base(15.0, hum))))
print()
if __name__ == "__main__":
_main()