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# 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
`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_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/

Comments or questions? Please subscribe to the pywws mailing list http://groups.google.com/group/pywws and let us know.

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