feat(at): Added apparent temperature(AT)

* feat(at): Added apparent temperature(AT).

* style(at): Updated to follow the style guide.
A minor update to improve code efficiency.

ladybug_comfort/apparent.py

@@ -0,0 +1,99 @@
+# coding=utf-8
+"""Utility functions for calculating the Apparent Temperature (AT)."""
+from __future__ import division
+
+import math
+
+
+def apparent_temperature(ta, rh, ws):
+    """Calculate apparent temperature (AT) from air temperature, relative humidity,
+     and wind speed.
+
+    The Australian Apparent Temperature (AT) is a type of heat index that was used by
+    the Australian Bureau of Meteorology (ABM). It is based on a mathematical model
+    published by Robert G. Steadman in 1994 [1]. Two forms of the model are available,
+    one including radiation and one without. This algorithm uses the non-radiation
+    version. [2]
+
+    Note:
+        [1] Steadman, R. G. (1994). Norms of apparent temperature in Australia. Aust.
+        Met. Mag, 43, 1-16.
+        [2] Thermal Comfort observations. (n.d.). Retrieved May 20, 2016,
+        from http://www.bom.gov.au/info/thermal_stress/
+
+    Args:
+        ta: Air temperature [C]
+        rh: Relative humidity [%]
+        ws: Wind speed (km /h)
+
+    Returns:
+        at: Apparent Temperature[C]
+    """
+
+    # e =  Water vapour pressure (hPa) [humidity]
+    e = (rh / 100) * 6.105 * math.exp((17.27 * ta) / (237.7 + ta))
+    at = ta + (0.33 * e) - (0.70 * ws) - 4.00
+
+    return at
+
+
+def apparent_temperature_warning_category(at):
+    """Get the category of apparent suggestion associated with a given apparent
+    temperature (AT).
+
+    Categories to indicate apparent suggestion:
+        4 = (>40 C) Minimal clothing; sun protection required.
+        3 = (35-40 C) Minimal clothing; sun protection as needed.
+        2 = (30-35 C) Short sleeve, shirt and shorts.
+        1 = (25-30 C) Light undershirt.
+        0 = (20-25 C) Cotton-type slacks (pants).
+        -1 = (15-20 C) Normal office wear.
+        -2 = (10-15 C) Thin or sleeveless sweater.
+        -3 = (5-10 C) Sweater. Thicker underwear.
+        -4 = (0-5 C) Coat and sweater.
+        -5 = (-5-0 C) Overcoat. Wind protection as needed.
+        -6 = (<-5 C) Overcoat. Head insulation. Heavier footwear.
+
+    Args:
+        at: Apparent temperature [C]
+
+    Returns:
+        category: An integer indicating the level of warning associated with the
+            heat index. Values are one of the following:
+                4 = Minimal clothing.
+                3 = Minimal clothing.
+                2 = Short sleeve, shirt and shorts.
+                1 = Light undershirt.
+                0 = Cotton-type slacks (pants).
+                -1 = Normal office wear.
+                -2 = Thin or sleeveless sweater.
+                -3 = Sweater. Thicker underwear.
+                -4 = Coat and sweater.
+                -5 = Overcoat.
+                -6 = Overcoat.
+    """
+
+    if at > 40:
+        category = 4
+    elif at > 35:
+        category = 3
+    elif at > 30:
+        category = 2
+    elif at > 25:
+        category = 1
+    elif at > 20:
+        category = 0
+    elif at > 15:
+        category = -1
+    elif at > 10:
+        category = -2
+    elif at > 5:
+        category = -3
+    elif at > 0:
+        category = -4
+    elif at > -5:
+        category = -5
+    else:
+        category = -6
+
+    return category

tests/apparent_test.py

@@ -0,0 +1,22 @@
+# coding utf-8
+import pytest
+
+from ladybug_comfort.apparent import apparent_temperature, apparent_temperature_warning_category
+
+
+def test_apparent_temperature():
+    """Test the apparent_temperature function."""
+    assert apparent_temperature(32, 85, 10) == pytest.approx(34.290083, rel=1e-3)
+    assert apparent_temperature(20, 50, 15) == pytest.approx(9.3482423, rel=1e-3)
+
+    assert apparent_temperature_warning_category(60) == 4
+    assert apparent_temperature_warning_category(40) == 3
+    assert apparent_temperature_warning_category(35) == 2
+    assert apparent_temperature_warning_category(26) == 1
+    assert apparent_temperature_warning_category(25) == 0
+    assert apparent_temperature_warning_category(16) == -1
+    assert apparent_temperature_warning_category(11) == -2
+    assert apparent_temperature_warning_category(6) == -3
+    assert apparent_temperature_warning_category(5) == -4
+    assert apparent_temperature_warning_category(0) == -5
+    assert apparent_temperature_warning_category(-5) == -6