[BME680] Fix elevation compensation + add 2 conversion commands

Also added 2 commands:
- Altitude(air,sea): `%c_alt_pres_sea%(850,1000)` = `1350.03` meter.
- PressureElevation(air,alt): `%c_sea_pres_alt%(850,1350.03)` =  1000.00 hPa

docs/source/Reference/SystemVariable.rst

@@ -172,6 +172,12 @@ The conversion always outputs a string, but not all of these can be converted ba
    * - Dew point(T,H): ``%c_dew_th%(18.6,67)``
      - Dew point(T,H): ``12.31``
      - Compute dew point given 2 values, temperature and relative humidity
+   * - Altitude(air,sea): ``%c_alt_pres_sea%(850,1000)``
+     - Altitude(air,sea): ``1350.03``
+     - Compute Altitude (m) given 2 values, atmospheric pressure and pressure at sea level (hPa). (Added: 2021/04/27)
+   * - PressureElevation(air,alt): ``%c_sea_pres_alt%(850,1350.03)``
+     - PressureElevation(air,alt): ``1000.00``
+     - Compensate air pressure for measured atmospheric pressure (hPa) and given altitude (m). (Added: 2021/04/27)
    * - cm to imperial: ``%c_cm2imp%(190)``
      - cm to imperial: ``6'2.8"``
      - Centimeter to imperial units

src/_P006_BMP085.ino

@@ -90,9 +90,7 @@ boolean Plugin_006(byte function, struct EventStruct *event, String& string)
 
           if (elev != 0)
           {
-            pressure = P006_data->pressureElevation(
-              pressure,
-              elev);
+            pressure = pressureElevation(pressure, elev);
           }
           UserVar[event->BaseVarIndex + 1] = pressure;
 

src/_P028_BME280.ino

@@ -151,7 +151,7 @@ boolean Plugin_028(byte function, struct EventStruct *event, String& string)
         const int elev = PCONFIG(1);
 
         if (elev != 0) {
-          UserVar[event->BaseVarIndex + 2] = P028_data->pressureElevation(elev);
+          UserVar[event->BaseVarIndex + 2] = pressureElevation(P028_data->last_press_val, elev);
         } else {
           UserVar[event->BaseVarIndex + 2] = P028_data->last_press_val;
         }

src/_P032_MS5611.ino

@@ -101,11 +101,11 @@ boolean Plugin_032(byte function, struct EventStruct *event, String& string)
           P032_data->readout();
 
           UserVar[event->BaseVarIndex] = P032_data->ms5611_temperature / 100;
-          int elev = PCONFIG(1);
-
-          if (elev)
+          
+          const int elev = PCONFIG(1);
+          if (elev != 0)
           {
-            UserVar[event->BaseVarIndex + 1] = P032_data->pressureElevation(P032_data->ms5611_pressure, elev);
+            UserVar[event->BaseVarIndex + 1] = pressureElevation(P032_data->ms5611_pressure, elev);
           } else {
             UserVar[event->BaseVarIndex + 1] = P032_data->ms5611_pressure;
           }

src/_P106_BME680.ino

@@ -132,8 +132,15 @@ boolean Plugin_106(byte function, struct EventStruct *event, String& string)
 
         UserVar[event->BaseVarIndex + 0] = P106_data->bme.temperature;
         UserVar[event->BaseVarIndex + 1] = P106_data->bme.humidity;
-        UserVar[event->BaseVarIndex + 2] = P106_data->bme.pressure / 100.0f;
         UserVar[event->BaseVarIndex + 3] = P106_data->bme.gas_resistance / 1000.0f;
+
+        const int elev = PCONFIG(1);
+        if (elev != 0)
+        {
+          UserVar[event->BaseVarIndex + 2] = pressureElevation(P106_data->bme.pressure / 100.0f, elev);
+        } else {
+          UserVar[event->BaseVarIndex + 2] = P106_data->bme.pressure / 100.0f;
+        }
       }
 
       success = true;

src/src/Helpers/Convert.cpp

@@ -181,6 +181,34 @@ float compute_humidity_from_dewpoint(float temperature, float dew_temperature) {
 }
 
 
+
+/********************************************************************************************\
+   Compensate air pressure for given altitude (in meters)
+ \*********************************************************************************************/
+float pressureElevation(float atmospheric, float altitude) {
+  // Equation taken from BMP180 datasheet (page 16):
+  //  http://www.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf
+
+  // Note that using the equation from wikipedia can give bad results
+  // at high altitude.  See this thread for more information:
+  //  http://forums.adafruit.com/viewtopic.php?f=22&t=58064
+  return atmospheric / pow(1.0f - (altitude / 44330.0f), 5.255f);
+}
+
+float altitudeFromPressure(float atmospheric, float seaLevel)
+{
+  // Equation taken from BMP180 datasheet (page 16):
+  //  http://www.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf
+
+  // Note that using the equation from wikipedia can give bad results
+  // at high altitude.  See this thread for more information:
+  //  http://forums.adafruit.com/viewtopic.php?f=22&t=58064
+  return 44330.0f * (1.0f - pow(atmospheric / seaLevel, 0.1903f));
+}
+
+
+
+
 /********************************************************************************************\
    In memory convert float to long
  \*********************************************************************************************/

src/src/Helpers/Convert.h

@@ -38,6 +38,19 @@ float compute_dew_point_temp(float temperature, float humidity_percentage);
 // f = 100 * ((112 - 0.1*T + Td) / (112 + 0.9 * T))^8
 float compute_humidity_from_dewpoint(float temperature, float dew_temperature);
 
+/********************************************************************************************\
+   Compensate air pressure for measured atmospheric
+      pressure (in hPa) and given altitude (in meters)
+ \*********************************************************************************************/
+float pressureElevation(float atmospheric, float altitude);
+
+/********************************************************************************************\
+  Calculates the altitude (in meters) from the specified atmospheric
+      pressure (in hPa), and sea-level pressure (in hPa).
+      @param  seaLevel      Sea-level pressure in hPa
+      @param  atmospheric   Atmospheric pressure in hPa
+ \*********************************************************************************************/
+float altitudeFromPressure(float atmospheric, float seaLevel);
 
 /********************************************************************************************\
    In memory convert float to long

src/src/Helpers/StringConverter.cpp

@@ -904,6 +904,8 @@ void parseStandardConversions(String& s, bool useURLencode) {
   float arg2 = 0.0f;
   SMART_CONV(F("%c_dew_th%"), toString(compute_dew_point_temp(arg1, arg2), 2))
   SMART_CONV(F("%c_u2ip%"),   formatUnitToIPAddress(arg1, arg2))
+  SMART_CONV(F("%c_alt_pres_sea%"), toString(altitudeFromPressure(arg1, arg2), 2))
+  SMART_CONV(F("%c_sea_pres_alt%"), toString(pressureElevation(arg1, arg2), 2))
   #undef SMART_CONV
 }
 

src/src/PluginStructs/P006_data_struct.cpp

@@ -130,8 +130,4 @@ float P006_data_struct::readTemperature(void)
   return temp;
 }
 
-float P006_data_struct::pressureElevation(float atmospheric, int altitude) {
-  return atmospheric / pow(1.0f - (altitude / 44330.0f), 5.255f);
-}
-
 #endif // ifdef USES_P006

src/src/PluginStructs/P006_data_struct.h

@@ -18,9 +18,6 @@ struct P006_data_struct : public PluginTaskData_base {
 
   float    readTemperature(void);
 
-  float    pressureElevation(float atmospheric,
-                             int   altitude);
-
   uint8_t  oversampling = BMP085_ULTRAHIGHRES;
   int16_t  ac1, ac2, ac3, b1, b2, mb, mc, md = 0;
   uint16_t ac4, ac5, ac6 = 0;

src/src/PluginStructs/P028_data_struct.cpp

@@ -397,22 +397,4 @@ float P028_data_struct::readHumidity()
   return h / 1024.0f;
 }
 
-float P028_data_struct::Plugin_028_readAltitude(float seaLevel)
-{
-  // Equation taken from BMP180 datasheet (page 16):
-  //  http://www.adafruit.com/datasheets/BST-BMP180-DS000-09.pdf
-
-  // Note that using the equation from wikipedia can give bad results
-  // at high altitude.  See this thread for more information:
-  //  http://forums.adafruit.com/viewtopic.php?f=22&t=58064
-
-  float atmospheric = readPressure() / 100.0f;
-
-  return 44330.0f * (1.0f - pow(atmospheric / seaLevel, 0.1903f));
-}
-
-float P028_data_struct::pressureElevation(int altitude) {
-  return last_press_val / pow(1.0f - (altitude / 44330.0f), 5.255f);
-}
-
 #endif // ifdef USES_P028

src/src/PluginStructs/P028_data_struct.h

@@ -156,19 +156,6 @@ struct P028_data_struct : public PluginTaskData_base {
   // **************************************************************************/
   float readHumidity();
 
-  // **************************************************************************/
-  // Calculates the altitude (in meters) from the specified atmospheric
-  //    pressure (in hPa), and sea-level pressure (in hPa).
-  //    @param  seaLevel      Sea-level pressure in hPa
-  //    @param  atmospheric   Atmospheric pressure in hPa
-  // **************************************************************************/
-  float Plugin_028_readAltitude(float seaLevel);
-
-  // **************************************************************************/
-  // MSL pressure formula
-  // **************************************************************************/
-  float pressureElevation(int altitude);
-
   bme280_uncomp_data uncompensated;
   bme280_calib_data  calib;
   float              last_hum_val      = 0.0f;

src/src/PluginStructs/P032_data_struct.cpp

@@ -117,11 +117,5 @@ void P032_data_struct::readout() {
   ms5611_pressure     = (((D1 * SENS) / (1 << 21) - Offset) / (1 << 15)); // FIXME TD-er: This is computed twice, is that correct?
 }
 
-// **************************************************************************/
-// MSL pressure formula
-// **************************************************************************/
-double P032_data_struct::pressureElevation(double atmospheric, int altitude) {
-  return atmospheric / pow(1.0f - (altitude / 44330.0f), 5.255f);
-}
 
 #endif // ifdef USES_P032

src/src/PluginStructs/P032_data_struct.h

@@ -35,12 +35,6 @@ public:
   // **************************************************************************/
   void readout();
 
-  // **************************************************************************/
-  // MSL pressure formula
-  // **************************************************************************/
-  double pressureElevation(double atmospheric,
-                           int    altitude);
-
   uint8_t      i2cAddress;
   unsigned int ms5611_prom[8]     = { 0 };
   double       ms5611_pressure    = 0;

src/src/WebServer/SysVarPage.cpp

@@ -203,6 +203,8 @@ void handle_sysvars() {
   addSysVar_html(F("{D}C to {D}F: %c_c2f%(20.4)"));
   addSysVar_html(F("m/s to Bft:   %c_ms2Bft%(5.1)"));
   addSysVar_html(F("Dew point(T,H): %c_dew_th%(18.6,67)"));
+  addSysVar_html(F("Altitude(air,sea): %c_alt_pres_sea%(850,1000)"));
+  addSysVar_html(F("PressureElevation(air,alt): %c_sea_pres_alt%(850,1350.03)"));
   addFormSeparator(3);
   addSysVar_html(F("cm to imperial: %c_cm2imp%(190)"));
   addSysVar_html(F("mm to imperial: %c_mm2imp%(1900)"));