More Earth-related functions

src/earth.h

@@ -6,10 +6,20 @@
 #include <stdlib.h>
 #include <math.h>
 
+const double PI = 3.14159265365358979323;
+/**
+* Earth constants...
+*/
+const double EQ_RADIUS = 6378.14;
+const double FLATTENING = 1.0 / 298.257;
+const double POL_RADIUS = 6356.755;
+const double RAD_RATIO = 1 - FLATTENING;
+const double MERID_ECC = 0.08181922;
 /**
 * @struct
 * A representation of the Earth
 * with some geometrical properties
+* @todo Useless?
 */
 struct Earth {
 	double a; /*!< The Earth's equatorial radius in km */
@@ -17,16 +27,15 @@ struct Earth {
     double b; /*!< The Earth's polar radius in km */
 	double e; /*!< The eccentricity of Earth's meridian */
 };
-
 /**
 * @struct
 * Representation of geographical
 * latitude
 */
 struct Latitude {
-    short degrees;
-    short arcmins;
-    double arcsecs;
+    short degrees;  /*!< Latitude degrees as an integer */
+    short arcmins;  /*!< Latitude arc minutes as an integer */
+    double arcsecs; /*!< Latitude arc seconds as decimal */
 };
 /**
 * @struct
@@ -36,27 +45,26 @@ struct Latitude {
 struct Location {
     struct Latitude lat; /*!< The location's geographical latitude */
     double h; /*!< Observer's height above sea level in m */
-    double r_sin_phi_p; /*!< Earth's radius times sin(geocentric latitude) */
-    double r_cos_phi_p; /*!< Earth's radius times cos(geocentric latitude) */
+    double r_sin_phi_p; /*!< Earth's radius times sin(geocentric_latitude) */
+    double r_cos_phi_p; /*!< Earth's radius times cos(geocentric_latitude) */
 };
 
-struct Earth set_earth_values(struct Earth * earth);
+void set_earth_values(struct Earth * earth);
 double lat_to_dec(struct Latitude lat);
+double r_sin_phi(double h, double decimal_lat);
 struct Latitude dec_to_lat(double dec_lat);
 struct Location set_location_params(struct Location * loc);
+
 /**
 * @fn
 * Initializes an Earth structure
-* @param *earth The Earth struct pointer
+* @todo Even more useless??
 */
-struct Earth set_earth_values(struct Earth * earth) {
-	earth->a = 6378.14; 
-	earth->f = 1 / 298.257; 
-    double f = earth->f;
-    earth->b = earth->a * (1 - earth->f); 
-	earth->e = sqrt(2*f - f*f);
-
-    return *earth;
+void set_earth_values(struct Earth * earth) {
+	earth->a = EQ_RADIUS; 
+	earth->f = FLATTENING; 
+    earth->b = POL_RADIUS; 
+	earth->e = MERID_ECC;
 }
 /**
 * @fn
@@ -70,4 +78,53 @@ double lat_to_dec(struct Latitude lat) {
 
     return lat.degrees + dec_minutes + dec_seconds;
 }
+/**
+* @fn
+* Calculates $\rho \sin{\phi}$ for
+* a location
+* @param h The location's height in meters
+* @param decimal_lat The location's decimal latitude in deg
+*/
+double rho_sin_phi(double h, double decimal_lat) {
+    // Convert lat from deg to radians
+    double lat_rad = decimal_lat * (PI / 180.);
+    double tan_u = RAD_RATIO * tan(lat_rad);
+    double u = atan(tan_u);
+    double rho_sin_phi = RAD_RATIO * sin(u) + (h / 6378140.) * sin(lat_rad);
+
+    return rho_sin_phi;
+}
+/**
+* @fn
+* Calculates $\rho \sin{\phi}$ for
+* a location
+* @param h The location's height in meters
+* @param decimal_lat The location's decimal latitude
+*/
+double rho_cos_phi(double h, double decimal_lat) {
+    // Convert lat from deg to radians
+    double lat_rad = decimal_lat * (PI / 180.);
+    double tan_u = RAD_RATIO * tan(lat_rad);
+    double u = atan(tan_u);
+
+    double rho_cos_phi = cos(u) + (h / 6378140) * cos(lat_rad);
+
+    return rho_cos_phi;
+}
+/**
+* @fn
+* Calculates and sets geographical parameters
+* related to a location
+* @param loc The Location to set
+* @param lat The location's Latitude
+* @param h The location's height in meters
+*/
+struct Location set_location_params(struct Location * loc) {
+    double decimal_lat = lat_to_dec(loc->lat);
+
+    loc->r_sin_phi_p = rho_sin_phi(loc->h, decimal_lat);
+    loc->r_cos_phi_p = rho_cos_phi(loc->h, decimal_lat);
+
+    return *loc;
+}