Add HeatIndexmethod

Author: flamerten

Adafruit_BME280.cpp

@@ -447,6 +447,40 @@ float Adafruit_BME280::readAltitude(float seaLevel) {
   return 44330.0 * (1.0 - pow(atmospheric / seaLevel, 0.1903));
 }
 
+/*!
+ *   Computes Heat Index based on https://byjus.com/heat-index-formula/
+ *
+ *   @param isCelcius - if true return Heat Index in degrees celcius else return in Farenheit
+ */
+float Adafruit_BME280::readHeatIndex(bool isCelcius){
+  float tempF = readTemperature() * 1.8 + 32;
+  float humidity = readHumidity();
+  float hi = 0.5 * (tempF + 61.0 + ((tempF - 68.0) * 1.2) + (humidity * 0.094));
+
+  if (hi > 79) {
+    hi = -42.379 + 2.04901523 * tempF + 10.14333127 * humidity +
+         -0.22475541 * tempF * humidity +
+         -0.00683783 * pow(tempF, 2) +
+         -0.05481717 * pow(humidity, 2) +
+         0.00122874 * pow(tempF, 2) * humidity +
+         0.00085282 * tempF * pow(humidity, 2) +
+         -0.00000199 * pow(tempF, 2) * pow(humidity, 2);
+
+    if ((humidity < 13) && (tempF >= 80.0) &&
+        (tempF <= 112.0))
+      hi -= ((13.0 - humidity) * 0.25) *
+            sqrt((17.0 - abs(tempF - 95.0)) * 0.05882);
+
+    else if ((humidity > 85.0) && (tempF >= 80.0) &&
+             (tempF <= 87.0))
+      hi += ((humidity - 85.0) * 0.1) * ((87.0 - tempF) * 0.2);
+  }  
+
+  if(isCelcius) return (hi - 32) * 0.5556; //convert back to celcius
+  else return hi;
+
+}
+
 /*!
  *   Calculates the pressure at sea level (in hPa) from the specified
  * altitude (in meters), and atmospheric pressure (in hPa).

Adafruit_BME280.h

@@ -229,6 +229,8 @@ class Adafruit_BME280 {
   float readTemperature(void);
   float readPressure(void);
   float readHumidity(void);
+  float readHeatIndex(bool isCelcius);
+
 
   float readAltitude(float seaLevel);
   float seaLevelForAltitude(float altitude, float pressure);