Add USSA 1976 model

include/sta/models/altitude.hpp

@@ -0,0 +1,58 @@
+#ifndef INC_MODELS_ALTITUDE_
+#define INC_MODELS_ALTITUDE_
+
+#include <sta/math/probability/randomVariable.hpp>
+
+namespace sta
+{
+namespace models {
+		class BarometricFormula
+		{
+            /**
+             * @brief Get the altitude from the pressure using the barometric formula. The model is valid for altitudes up to leat 9 km.
+             *
+             * @param p Pressure in hPa
+             * @return Altitude in meters
+             */
+		public:
+            /*
+            * @brief Constructor for the Barometric Formula
+            * @param pRef Reference pressure in hPa
+            * @param hRef Reference altitude in meters
+            */
+			BarometricFormula(float pRef = 1013.25, float hRef = 0);
+
+            /* 
+            * @brief Get the altitude from the pressure using the barometric formula
+            * @param p Pressure in hPa
+            * @return Altitude in meters
+            */
+            float getAltitude(float p);
+
+		private:
+			float p0_;
+		};
+
+        namespace USSA1976
+        {
+            /**
+             * @brief Get the altitude from the pressure using the U.S. Standard Atmosphere 1976 model (https://ntrs.nasa.gov/search.jsp?R=19770009539)
+             * and the barometric formula for multiple layers. The model is valid for altitudes up to at leat 71 km. See https://en.wikipedia.org/wiki/Barometric_formula for more information.
+             *
+             * @param p Pressure in hPa
+             * @return Altitude in meters
+             */
+            float getAltitude(float p);
+            /**
+             * @brief Get the altitude as Gaussian Random Variable from the pressure as Gaussian Random Variable using the U.S. Standard Atmosphere 1976 model (https://ntrs.nasa.gov/search.jsp?R=19770009539)
+             * and the barometric formula for multiple layers. The model is valid for altitudes up to at leat 71 km. See https://en.wikipedia.org/wiki/Barometric_formula for more information.
+             *
+             * @param p Pressure in hPa as a Gaussian Random Variable
+             * @return Altitude in meters as a Gaussian Random Variable
+             */
+            sta::math::probability::grv getAltitude(sta::math::probability::grv p);
+        }  // namespace USSA1976
+}  // namespace models
+}  // namespace sta
+
+#endif //INC_MODELS_ALTITUDE_

include/sta/models/constants.hpp

@@ -0,0 +1,12 @@
+#ifndef STA_MODELS_CONSTANTS_HPP
+#define STA_MODELS_CONSTANTS_HPP
+
+//Altitude Constants
+
+#define STA_CONSTANT_R 8.3144598 //J/(mol*K)
+
+#define STA_CONSTANT_G_0 9.80665 //m/s^2
+
+#define STA_CONSTANT_M 0.028964425278793993 //kg/mol
+
+#endif //STA_MODELS_CONSTANTS_HPP