Fix too large troposphere corrections when pos is deep inside the Earth

Author: nsirola

src/troposphere.c

@@ -276,7 +276,7 @@ static double calc_param(double lat, double doy, const double *avg_lut, const do
  *   -# UNB Neutral Atmosphere Models: Development and Performance. R Leandro,
  *      M Santos, and R B Langley
  *
- * \param doy Day of the year at which to calculate tropospheric delay [day]
+ * \param t_gps GPS time at which to calculate tropospheric delay [gps_time]
  * \param lat Latitude of the receiver [rad]
  * \param h Orthometric height of the receiver (height above the geoid) [m]
  * \param el Elevation of the satellite [rad]
@@ -289,6 +289,11 @@ double calc_troposphere(const gps_time_t *t_gps, double lat, double h,
   lat *= R2D;
   el *= R2D;
 
+  /* truncate negative altitudes */
+  if (h < 0) {
+    h = 0.0;
+  }
+
   /* compute day of year from gps time */
   double doy = (double) gps2doy(t_gps);
 

tests/check_troposphere.c

@@ -59,6 +59,22 @@ START_TEST(test_calc_troposphere)
 	fail_unless(fabs(d_tropo - d_true) < d_tol,
 		      "Distance didn't match hardcoded correct values %0.5f. Saw: %.5f\n",
 		      d_true, d_tropo);
+
+	/* elevation sanity tests */
+	double const max_tropo_correction = 30.0;
+	h = -5000;
+	d_tropo = calc_troposphere(&t, lat, h, el);
+
+	fail_unless(fabs(d_tropo) < max_tropo_correction,
+		      "Sanity test fail at elevation %0.5f. : Correction was %.5f\n",
+		      h, d_tropo);
+
+	h = 12000;
+	d_tropo = calc_troposphere(&t, lat, h, el);
+
+	fail_unless(fabs(d_tropo) < max_tropo_correction,
+		      "Sanity test fail at elevation %0.5f. : Correction was %.5f\n",
+		      h, d_tropo);
 }
 END_TEST