add basic refraction correction

1 files changed, 16 insertions, 3 deletions

diff --git a/src/Panorama.cxx b/src/Panorama.cxx
index 32e14f4..49010f5 100644
--- a/src/Panorama.cxx
+++ b/src/Panorama.cxx
@@ -428,15 +428,28 @@ Panorama::alpha(const Hill *m) {
 	return fmod(atan2(sin_alph, cos_alph) + 2.0 * pi_d, 2.0 * pi_d);
 }
 
+double
+Panorama::refraction_change(const Hill *m) {
+	double a, b, c, alpha = 6.5 / 1000.0, T0 = 10.0;
+
+	a = 2.9e-4 * exp (-view_height / 10000.0) / (1.0 + 2.9 * T0 / 760.0);
+	b = 2.9 * alpha / (760.0 * (1.0 + 2.9 * T0 / 760.0));
+	c = a * (b - 1.0 / 10000.0);
+
+	return (c * get_real_distance(m) / (2.0 * (1.0 + a)));
+}
 
 double
 Panorama::nick(const Hill *m) {
-	double b, c;
+	double b, c, theta = refraction_change(m);
 
 	b = m->height + get_earth_radius(m->phi);
 	c = view_height + get_earth_radius(view_phi);
 
-	return atan((cos(m->dist) * b - c) / (sin(m->dist) * b));
+if (get_real_distance(m) < 200000)
+fprintf(stderr, "=== %s, %g\n", m->name, theta);
+	
+	return atan((cos(m->dist) * b - c) / (sin(m->dist) * b)) - theta;
 }
 
 // return local distance to center of WGS84 ellipsoid
@@ -452,7 +465,7 @@ Panorama::get_earth_radius(double phi) {
 }
 
 double
-Panorama::get_real_distance(Hill *m) {
+Panorama::get_real_distance(const Hill *m) {
 	double a, b, c, gam;
 
 	a = view_height + get_earth_radius(view_phi);