add note about refraction to README

2 files changed, 9 insertions, 1 deletions

diff --git a/README b/README
index 85c4097..1c02e0f 100644
--- a/README
+++ b/README
@@ -125,6 +125,14 @@ not shown by default, but you can enable the display of hidden objects using
 the Option->Show Hidden menu entry. Hidden objects and hidden GPS way points
 are displayed in blue.
 
+Refraction
+==========
+
+Refraction caused by temperature and density gardients in the atmosphere is
+taken into account according to the approximation described by Tom Chester in:
+http://tchester.org/sgm/analysis/peaks/refraction_calculation.html
+under the assumption of a temperature change of 6.5°C per 1000m and a
+temperature T0 at view point level of 10°C.
 
 Stitching
 =========
diff --git a/src/Panorama.cxx b/src/Panorama.cxx
index a072fd0..aa358ec 100644
--- a/src/Panorama.cxx
+++ b/src/Panorama.cxx
@@ -433,7 +433,7 @@ Panorama::alpha(const Hill *m) {
 
 double
 Panorama::refraction(const Hill *m) {
-	double a, b, c, alpha = 6.5, T0 = 0.0;
+	double a, b, c, alpha = 6.5, 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));