Ported FMI "feels like" temperature calculation. (#52)

* Ported FMI "feels like" temperature calculation.

Bumped version to 0.2.1

* Replaced short variable names with longer

* Updated README to mention "feels like" temperature

README.md

@@ -93,6 +93,7 @@ FMI provides the following commonly used information:
 - Cloud coverage (%)
 - Precipitation intensity (mm/h)
 - Symbol [Documentation in Finnish](https://www.ilmatieteenlaitos.fi/latauspalvelun-pikaohje)
+- Feels like temperature (°C), calculated from weather data [Documentation in Finnish](https://tietopyynto.fi/files/foi/2940/feels_like-1.pdf)
 
 
 There are also other information available. Check [models.py](fmi_weather_client/models.py) and FMI documentation for

fmi_weather_client/models.py

@@ -65,6 +65,9 @@ class WeatherData(NamedTuple):
     geopotential_height: Value
     land_sea_mask: Value
 
+    # Calculated "feels like" temperature
+    feels_like: Value
+
 
 class Weather(NamedTuple):
     """Represents a weather"""

fmi_weather_client/parsers/forecast.py

@@ -138,10 +138,56 @@ def to_value(vals: Dict[str, float], variable_name: str, unit: str) -> Value:
         radiation_long_wave_surface_net_acc=to_value(values, 'RadiationNetSurfaceLWAccumulation', 'J/m²'),
         radiation_short_wave_diff_surface_acc=to_value(values, 'RadiationDiffuseAccumulation', 'J/m²'),  # Not supported
         geopotential_height=to_value(values, 'GeopHeight', 'm'),
-        land_sea_mask=to_value(values, 'LandSeaMask', '')  # Not supported
+        land_sea_mask=to_value(values, 'LandSeaMask', ''),  # Not supported
+        feels_like=Value(_feels_like(values), '°C')
         )
 
 
+def _feels_like(vals: Dict[str, float]) -> float:
+    # Feels like temperature, ported from:
+    # https://github.com/fmidev/smartmet-library-newbase/blob/master/newbase/NFmiMetMath.cpp#L535
+    # For more documentation see:
+    # https://tietopyynto.fi/tietopyynto/ilmatieteen-laitoksen-kayttama-tuntuu-kuin-laskentakaava/
+    # https://tietopyynto.fi/files/foi/2940/feels_like-1.pdf
+    temperature = vals.get("Temperature", None)
+    wind_speed = vals.get("WindSpeedMS", None)
+    humidity = vals.get("Humidity", None)
+    radiation = vals.get("RadiationGlobal", None)
+
+    if temperature is None:
+        return None
+    if wind_speed is None or wind_speed < 0.0 or humidity is None:
+        return temperature
+
+    # Wind chilling factor
+    chill = 15 + (1-15/37)*temperature + 15/37*pow(wind_speed+1, 0.16)*(temperature-37)
+    # Heat index
+    heat = _summer_simmer(temperature, humidity)
+
+    # Add corrections together
+    feels = temperature + (chill - temperature) + (heat - temperature)
+
+    # Perform radiation correction only when radiation is available
+    if radiation is not None:
+        absorption = 0.07
+        feels += 0.7 * absorption * radiation / (wind_speed + 10) - 0.25
+
+    return feels
+
+
+def _summer_simmer(temperature: float, humidity_percent: float):
+    if temperature <= 14.5:
+        return temperature
+
+    # Humidity value is expected to be on 0..1 scale
+    humidity = humidity_percent / 100.0
+    humidity_ref = 0.5
+
+    # Calculate the correction
+    return (1.8*temperature - 0.55*(1-humidity) * (1.8*temperature - 26) - 0.55*(1-humidity_ref)*26) \
+        / (1.8*(1 - 0.55*(1-humidity_ref)))
+
+
 def _float_or_none(value: Any) -> Optional[float]:
     """
     Get value as float. None if conversion fails.

setup.py

@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name="fmi-weather-client",
-    version="0.2.0",
+    version="0.2.1",
     author="Mika Hiltunen",
     author_email="[email protected]",
     description="Library for fetching weather information from Finnish Meteorological Institute (FMI)",

test/test_parsers_forecast.py

@@ -1,5 +1,6 @@
 import unittest
 from fmi_weather_client.parsers.forecast import _float_or_none
+from fmi_weather_client.parsers.forecast import _feels_like
 
 
 class ForecastParserTest(unittest.TestCase):
@@ -11,3 +12,28 @@ def test_float_or_none(self):
         self.assertEqual(_float_or_none("0"), 0.0)
         self.assertEqual(_float_or_none(""), None)
         self.assertEqual(_float_or_none("NaN"), None)
+
+    def test_feels_like(self):
+        # Partial data
+        self.assertEqual(_feels_like({}), None)
+        self.assertEqual(_feels_like({"Temperature": 10}), 10)
+        self.assertEqual(_feels_like({"Temperature": 10, "WindSpeedMS": 10}), 10)
+        self.assertEqual(_feels_like({"Temperature": 10, "Humidity": 10}), 10)
+        # Without radiation
+        self.assertAlmostEqual(_feels_like({"WindSpeedMS": 5, "Humidity": 50, "Temperature": 0}), -4.980, places=3)
+        self.assertAlmostEqual(_feels_like({"WindSpeedMS": 5, "Humidity": 50, "Temperature": -5}), -10.653, places=3)
+        self.assertAlmostEqual(_feels_like({"WindSpeedMS": 5, "Humidity": 50, "Temperature": 25}), 23.385, places=3)
+        self.assertAlmostEqual(_feels_like({"WindSpeedMS": 5, "Humidity": 90, "Temperature": 25}), 26.588, places=3)
+        # With radiation
+        self.assertAlmostEqual(
+            _feels_like({"WindSpeedMS": 0, "Humidity": 50, "Temperature": 0, "RadiationGlobal": 0}),
+            -0.250, places=3)
+        self.assertAlmostEqual(
+            _feels_like({"WindSpeedMS": 0, "Humidity": 50, "Temperature": 10, "RadiationGlobal": 50}),
+            9.995, places=3)
+        self.assertAlmostEqual(
+            _feels_like({"WindSpeedMS": 5, "Humidity": 50, "Temperature": 0, "RadiationGlobal": 800}),
+            -2.617, places=3)
+        self.assertAlmostEqual(
+            _feels_like({"WindSpeedMS": 5, "Humidity": 50, "Temperature": 25, "RadiationGlobal": 425}),
+            24.523, places=3)