improve windchill() and heatIndex() (#15)

* improve windchill() and heatIndex()

README.md

@@ -79,6 +79,17 @@ else ==> formula assumes wind speed @ 1.5 meter
 - **float WindChill_C_mps(float Celsius, float meterPerSecond, bool convert = true)**
 
 
+Indicative table (subjective).
+
+| wind chill °C | description          |
+|:-------------:|:---------------------|
+|  > -10        |  cold                |
+|  -10 .. -25   |  very cold !         |
+|  -25 .. -35   |  very very cold !    |
+|  -35 .. -55   |  chance of frostbite |
+|  < -55        |  serious dangerous   |
+
+
 ## temperatureConverter
 
 Since version 0.3.2 a temperature convertor class is added to convert to and from 

examples/heatindexC_table/heatindexC_table.ino

@@ -38,7 +38,7 @@ void setup()
     Serial.println();
   }
   Serial.println();
-  Serial.println();
+  Serial.println(heatIndexC(20, 50));
 
   Serial.print("Done...");
 }
@@ -50,4 +50,3 @@ void loop()
 
 
 // -- END OF FILE --
-

examples/heatindexC_test/heatindexC_test.ino

@@ -1,7 +1,7 @@
 //
 //    FILE: heatindexC_test.ino
 //  AUTHOR: Rob Tillaart
-// PURPOSE: demo
+// PURPOSE: demo - test average performance per call in micros.
 //    DATE: 2020-04-04
 
 
@@ -21,16 +21,19 @@ void setup()
 
   Serial.println(heatIndexC(25, 50), 2);
 
-  start = millis();
+  start = micros();
+  int cnt = 0;
   for (int cel = 10; cel < 80; cel++)
   {
     for (int hum = 1; hum < 100; hum++)
     {
       hi = heatIndexC(cel, hum);
+      cnt++;
     }
   }
-  duration1 = millis() - start;
+  duration1 = micros() - start;
   Serial.println(duration1);
+  Serial.println(1.0 * duration1 / cnt);
 
   Serial.print("Done...");
 }
@@ -42,4 +45,3 @@ void loop()
 
 
 // -- END OF FILE --
-

examples/windChill_test/windChill_test.ino

@@ -0,0 +1,35 @@
+//
+//    FILE: windChill_test.ino
+//  AUTHOR: Rob Tillaart
+// PURPOSE: demo
+//    DATE: 2022-01-09
+
+
+#include "temperature.h"
+
+void setup()
+{
+  Serial.begin(115200);
+  Serial.println(__FILE__);
+
+  Serial.println(WindChill_F_mph (0, 10, true), 3);
+  Serial.println(WindChill_C_kmph(0, 10, true), 3);
+  Serial.println(WindChill_C_mps (0, 10, true), 3);
+  Serial.println(WindChill_C_kmph(-20, 5, true), 3);
+
+
+  Serial.println(WindChill_F_mph (0, 10, false), 3);
+  Serial.println(WindChill_C_kmph(0, 10, false), 3);
+  Serial.println(WindChill_C_mps (0, 10, false), 3);
+
+
+  Serial.print("Done...");
+}
+
+
+void loop()
+{
+}
+
+
+// -- END OF FILE --

library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/Temperature"
   },
-  "version": "0.3.2",
+  "version": "0.3.3",
   "license": "MIT",
   "frameworks": "arduino",
   "platforms": "*",

library.properties

@@ -1,5 +1,5 @@
 name=Temperature
-version=0.3.2
+version=0.3.3
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=Library with weather related functions. 

temperature.h

@@ -1,7 +1,7 @@
 #pragma once
 //
 //    FILE: temperature.h
-// VERSION: 0.3.2
+// VERSION: 0.3.3
 //    DATE: 2015-03-29
 // PURPOSE: collection temperature functions
 //
@@ -23,9 +23,11 @@
 //  0.3.2   2022-01-08  Renamed Celcius to Celsius.
 //                      added a TempConvertor class for more exotic scales.
 //                      added baroToSeaLevel() - kudos to RobertDB59
+//  0.3.3   2022-01-09  added working limits to windchill() and heatIndex()
 
 
-#define TEMPERATURE_VERSION         (F("0.3.2"))
+
+#define TEMPERATURE_VERSION         (F("0.3.3"))
 
 
 inline float Fahrenheit(float celsius)
@@ -34,9 +36,9 @@ inline float Fahrenheit(float celsius)
 }
 
 
-inline float Celsius(float fahrenheit)
+inline float Celsius(float Fahrenheit)
 {
-  return (fahrenheit - 32) * 0.55555555555;   // 5.0 / 9.0 = 0.555...
+  return (Fahrenheit - 32) * 0.55555555555;   // 5.0 / 9.0 = 0.555...
 }
 
 
@@ -96,14 +98,16 @@ float humidex(float celsius, float dewPoint)
 
 // 0.3.0 => https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml 
 //          previous  https://en.wikipedia.org/wiki/Heat_index
-// TODO add valid range for TF & R
 // TF = temp in Fahrenheit
 // RH = relative humidity in %
 float heatIndex(float TF, float RH)
 {
-  float HI = 0;
+  //  Steadman's formula  ==> can be optimized :: HI = TF * 1.1 - 10.3 + RH * 0.047
+  float HI =  0.5 * (TF + 61.0 + ((TF - 68.0) * 1.2) + (RH * 0.094));
+
 
-  if (TF >= 80)
+  //  Rothfusz regression
+  if (HI >= 80)
   {
     const float c1 = -42.379;
     const float c2 =  2.04901523;
@@ -128,23 +132,21 @@ float heatIndex(float TF, float RH)
     {
       HI += ((RH - 85) / 10) * ((87 - TF) / 5);
     }
-    return HI;
   }
 
-  HI = 0.5 * (TF + 61.0 + ((TF - 68.0) * 1.2) + (RH * 0.094));
-
   return HI;
 }
 
 
 // 0.3.0 => https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml 
 //          previous  https://en.wikipedia.org/wiki/Heat_index
-// TODO add valid range for TF & RH
-// TODO optimize?
-float heatIndexC(float C, float humidity)
+// TC = temp in Celsius
+// RH = relative humidity in %
+float heatIndexC(float TC, float RH)
 {
-  float TF = Fahrenheit(C);
-  return Celsius(heatIndex(TF, humidity));
+  if ( (TC < 27) || (RH < 40)) return TC;
+  float TF = Fahrenheit(TC);
+  return Celsius(heatIndex(TF, RH));
 
 /*
   const float c1 = -8.78469475556;
@@ -167,25 +169,27 @@ float heatIndexC(float C, float humidity)
 
 
 // https://en.wikipedia.org/wiki/Wind_chill
-//    US     = Fahrenheit / miles
-//    METRIC = Celsius / meter/sec
+//    US     = Fahrenheit / miles / hour
+//    METRIC = Celsius    / meter / hour (sec)
 // wind speed @ 10 meter,
 // if convert is true => wind speed will be converted to 1.5 meter
 // else ==> formula assumes wind speed @ 1.5 meter
 
 
 // US
-float WindChill_F_mph(const float fahrenheit, const float milesPerHour, const bool convert = true)
+float WindChill_F_mph(const float Fahrenheit, const float milesPerHour, const bool convert = true)
 {
+  if ((milesPerHour < 3.0) || (Fahrenheit > 50)) return Fahrenheit;
   float windSpeed = milesPerHour;
   if (convert) windSpeed = pow(milesPerHour, 0.16);
-  return 35.74 + 0.6125 * fahrenheit + (0.4275 * fahrenheit - 35.75) * windSpeed;
+  return 35.74 + 0.6125 * Fahrenheit + (0.4275 * Fahrenheit - 35.75) * windSpeed;
 }
 
 
-// METRIC
+// METRIC - standard wind chill formula for Environment Canada
 float WindChill_C_kmph(const float Celsius, const float kilometerPerHour, const bool convert = true)
 {
+  if ((kilometerPerHour < 4.8) || (Celsius > 10)) return Celsius;
   float windSpeed = kilometerPerHour;
   if (convert) windSpeed = pow(kilometerPerHour, 0.16);
   return 13.12 + 0.6215 * Celsius + (0.3965 * Celsius - 11.37) * windSpeed;

test/unit_test_001.cpp

@@ -71,7 +71,7 @@ unittest(test_heatIndex)
   assertEqualFloat(14.050, heatIndex(20, 50), 0.001);
   assertEqualFloat(66.850, heatIndex(68, 50), 0.001);
   //  Celsius
-  assertEqualFloat(19.361, heatIndexC(20, 50), 0.001);
+  assertEqualFloat(20.000, heatIndexC(20, 50), 0.001);
 }
 
 
@@ -110,12 +110,16 @@ unittest(test_heatIndex_2)
 
 unittest(test_windChill)
 {
-  assertEqualFloat(107.108, WindChill_F_mph (100, 10, true), 0.001);
-  assertEqualFloat(40.8862, WindChill_C_kmph(37, 10, true),  0.001);
-  assertEqualFloat(41.9713, WindChill_C_mps (37, 10, true),  0.001);
-  assertEqualFloat(166.99,  WindChill_F_mph (100, 10, false), 0.001);
-  assertEqualFloat(69.1205, WindChill_C_kmph(37, 10, false),  0.001);
-  assertEqualFloat(154.934, WindChill_C_mps (37, 10, false),  0.001);
+  fprintf(stderr, "\n Fahrenheit\n");
+  assertEqualFloat( -15.9, WindChill_F_mph (0, 10, true), 0.1);
+  assertEqualFloat(-321.8, WindChill_F_mph (0, 10, false), 0.1);
+
+  fprintf(stderr, "\n Celsius\n");
+  assertEqualFloat(  -3.3, WindChill_C_kmph(0, 10, true), 0.1);
+  assertEqualFloat(  -7.1, WindChill_C_mps (0, 10, true), 0.1);
+  assertEqualFloat( -24.3, WindChill_C_kmph(-20, 5, true), 0.1);
+  assertEqualFloat(-100.5, WindChill_C_kmph(0, 10, false), 0.1);
+  assertEqualFloat(-396.2, WindChill_C_mps (0, 10, false), 0.1);
 }