Merge pull request #74 from jbrodovsky/jbrodovsky/issue44

Jbrodovsky/issue44

Author: jbrodovsky

core/src/earth.rs

@@ -72,48 +72,46 @@ pub const MAGNETIC_FIELD_STRENGTH: f64 = 3.12e-5; // T, reference mean magnetic
 pub const METERS_TO_DEGREES: f64 = 1.0 / (60.0 * 1852.0);
 /// Rough conversion factor from degrees to meters for latitude/longitude via nautical miles (1 degree ~ 60 nautical miles; 1 nautical mile ~ 1852 meters)
 pub const DEGREES_TO_METERS: f64 = 60.0 * 1852.0;
-/// Sea-level atmospheric pressure in pascals 
-pub const SEA_LEVEL_PRESSURE: f64 = 101325.0; // Pa, standard sea-level pressure
-/// Temperature lapse rate in Kelvin per meter
-pub const TEMPERATURE_LAPSE_RATE: f64 = 0.00976; // K/m, standard temperature lapse rate in the troposphere
-/// Constant-pressure specific heat
-pub const CONSTANT_PRESSURE_SPECIFIC_HEAT: f64 = 1004.68506; // J/(kg·K), specific heat at constant pressure for dry air
-/// Sea level standard temperature in Kelvin
-pub const SEA_LEVEL_STANDARD_TEMPERATURE: f64 = 288.15; // K, standard sea-level temperature
-/// Molar mass of dry air in kg/mol
-pub const MOLAR_MASS_DRY_AIR: f64 = 0.02896968; // kg/mol, molar mass of dry air
-/// Universal gas constant in J/(mol·K)
-pub const UNIVERSAL_GAS_CONSTANT: f64 = 8.314462618; // J/(mol·K), universal gas constant
-/// Calculate the barometric altitude from pressure and temperature
+/// Atmospheric pressure at sea level in Pascals ($P_0$)
+pub const SEA_LEVEL_PRESSURE: f64 = 101325.0;
+/// Standard temperature at sea level in Kelvin ($T_0$)
+pub const SEA_LEVEL_TEMPERATURE: f64 = 288.15; 
+/// Molar mass of dry air in kg/mol ($M$)
+pub const MOLAR_MASS_DRY_AIR: f64 = 0.0289644; 
+/// Universal gas constant in J/(mol·K) ($R_0$)
+pub const UNIVERSAL_GAS_CONSTANT: f64 = 8.314462618;
+/// Standard lapse rate in K/m ($L$)
+pub const STANDARD_LAPSE_RATE: f64 = 0.0065;
+/// Calculate a barometric altitude from a measured pressure
 /// 
-/// This function calculates the barometric altitude using the barometric formula, which relates
-/// the pressure at a given altitude to the pressure at sea level. The formula is based on the
-/// assumption of an isothermal atmosphere and the ideal gas law.
-/// 
-/// # Arguments
-/// - `pressure` - The atmospheric pressure at the given altitude in pascals
+/// This function calculates the altitude above sea level based on the measured pressure
+/// using the barometric formula. The formula assumes a standard atmosphere and uses the
+/// universal gas constant, standard lapse rate, and molar mass of dry air.
 /// 
+/// # Parameters
+/// - `pressure` - The measured pressure in Pascals
 /// # Returns
-/// The barometric altitude in meters
-pub fn barometric_altitude(pressure: f64) -> f64 {
-    let exponent: f64 = -((UNIVERSAL_GAS_CONSTANT * TEMPERATURE_LAPSE_RATE) / (G0 * MOLAR_MASS_DRY_AIR));
-    (SEA_LEVEL_STANDARD_TEMPERATURE / TEMPERATURE_LAPSE_RATE) * (pressure / SEA_LEVEL_PRESSURE) * exponent.exp()
+/// The calculated altitude in meters above sea level
+pub fn barometric_altitude(pressure: &f64) -> f64 {
+    let exponent: f64 = - (UNIVERSAL_GAS_CONSTANT * STANDARD_LAPSE_RATE) / (G * MOLAR_MASS_DRY_AIR);
+    (SEA_LEVEL_PRESSURE / STANDARD_LAPSE_RATE) * (pressure / SEA_LEVEL_PRESSURE - 1.0) * exponent.exp()
 }
-/// Calculates the relative barometric altitude from pressure and temperature
+/// Calculate the relative barometric altitude from a measured pressure
 /// 
-/// This function calculates the relative barometric altitude using the barometric formula,
-/// which relates the pressure at a given altitude to the pressure at a reference altitude.
-/// This is similar to how aircraft pressure altimeters work, where the preassure at a known
-/// altitude is used to calibrate the altimeter.
+/// This function calculates the relative altitude from a reference pressure using the
+/// barometric formula. The formula assumes a standard atmosphere and uses the universal 
+/// gas constant, standard lapse rate, and molar mass of dry air.
 /// 
-/// # Arguments
-/// - `pressure` - The measured atmospheric pressure
-/// - `initial_pressure` - The atmospheric pressure at the reference altitude in pascals
+/// # Parameters
+/// - `pressure` - The measured pressure in Pascals
+/// - `initial_pressure` - The reference pressure in Pascals
+/// - `average_temperature` - Optional average temperature in Kelvin (defaults to standard sea level temperature)
 /// 
 /// # Returns
-/// The relative barometric altitude in meters, i.e. the altitude relative to the reference.
-pub fn relative_barometric_altitude(pressure: f64, initial_pressure: f64) -> f64 {
-    ((UNIVERSAL_GAS_CONSTANT * SEA_LEVEL_PRESSURE) / (G0 * MOLAR_MASS_DRY_AIR)) * (initial_pressure / pressure).ln()
+/// The calculated relative altitude in meters above the reference pressure
+pub fn relative_barometric_altitude(pressure: f64, initial_pressure: f64, average_temperature: Option<f64>) -> f64 {
+    let average_temperature = average_temperature.unwrap_or(SEA_LEVEL_TEMPERATURE);
+    ((UNIVERSAL_GAS_CONSTANT * average_temperature) / (G * MOLAR_MASS_DRY_AIR)) * (initial_pressure / pressure).ln()
 }
 /// Convert a three-element vector to a skew-symmetric matrix
 ///