pywws.conversions

conversions.py - a set of functions to convert pywws native units (Centigrade, mm, m/s, hPa) to other popular units

Functions

apparent_temp(temp, rh, wind)	Compute apparent temperature (real feel), using formula from
cadhumidex(temp, humidity)	Calculate Humidity Index as per Canadian Weather Standards
cloud_base(temp, hum)	Calculate cumulus cloud base in metres, using formula from
cloud_ft(m)	Convert cloud base from metres to feet.
dew_point(temp, hum)	Compute dew point, using formula from http://en.wikipedia.org/wiki/Dew_point.
illuminance_wm2(lux)	Approximate conversion of illuminance in lux to solar radiation in W/m2
pressure_inhg(hPa)	Convert pressure from hectopascals/millibar to inches of mercury
pressure_trend_text(trend)	Convert pressure trend to a string, as used by the UK met office.
rain_inch(mm)	Convert rainfall from millimetres to inches
temp_f(c)	Convert temperature from Celsius to Fahrenheit
usaheatindex(temp, humidity, dew)	Calculate Heat Index as per USA National Weather Service Standards
wind_bft(ms)	Convert wind from metres per second to Beaufort scale
wind_chill(temp, wind)	Compute wind chill, using formula from
wind_kmph(ms)	Convert wind from metres per second to kilometres per hour
wind_kn(ms)	Convert wind from metres per second to knots
wind_mph(ms)	Convert wind from metres per second to miles per hour
winddir_average(data, threshold, min_count)	Compute average wind direction (in degrees) for a slice of data.
winddir_degrees(pts)	Convert wind direction from 0..15 to degrees
winddir_text(pts)	Convert wind direction from 0..15 to compass point text

pywws.conversions.illuminance_wm2(lux)

Approximate conversion of illuminance in lux to solar radiation in W/m2

pywws.conversions.pressure_inhg(hPa)

Convert pressure from hectopascals/millibar to inches of mercury

pywws.conversions.pressure_trend_text(trend)

Convert pressure trend to a string, as used by the UK met office.

pywws.conversions.rain_inch(mm)

Convert rainfall from millimetres to inches

pywws.conversions.temp_f(c)

Convert temperature from Celsius to Fahrenheit

pywws.conversions.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 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.

Parameters:

• data (pywws.DataStore.core_store) – a slice of pywws raw/calib or hourly data.
• threshold (float) – minimum average windspeed for there to be a valid wind direction.
• min_count (int) – minimum number of data items for there to be a valid wind direction.
• decay (float) – filter coefficient decay rate.

Return type:

float

pywws.conversions.winddir_degrees(pts)

Convert wind direction from 0..15 to degrees

pywws.conversions.winddir_text(pts)

Convert wind direction from 0..15 to compass point text

pywws.conversions.wind_kmph(ms)

Convert wind from metres per second to kilometres per hour

pywws.conversions.wind_mph(ms)

Convert wind from metres per second to miles per hour

pywws.conversions.wind_kn(ms)

Convert wind from metres per second to knots

pywws.conversions.wind_bft(ms)

Convert wind from metres per second to Beaufort scale

pywws.conversions.dew_point(temp, hum)

Compute dew point, using formula from http://en.wikipedia.org/wiki/Dew_point.

pywws.conversions.cadhumidex(temp, humidity)

Calculate Humidity Index as per Canadian Weather Standards

pywws.conversions.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%

pywws.conversions.wind_chill(temp, wind)

Compute wind chill, using formula from http://en.wikipedia.org/wiki/wind_chill

pywws.conversions.apparent_temp(temp, rh, wind)

Compute apparent temperature (real feel), using formula from http://www.bom.gov.au/info/thermal_stress/

pywws.conversions.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

pywws.conversions.cloud_ft(m)

Convert cloud base from metres to feet.

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