From 46435edf1954002929425e5135bdc507aa563e59 Mon Sep 17 00:00:00 2001
From: Erik Hofman <erik@ehofman.com>
Date: Tue, 27 Oct 2020 08:31:54 +0100
Subject: [PATCH] The fixed 60 degrees offset at EHAL turned out to be the
lattitude offset (actually 53.45 degrees): The moon seems to be dragging the
tide with an almost perfect 45 degrees 'bow-wave' along the equator.
---
src/Time/tide.cxx | 14 ++++++++++++--
src/Time/tide.hxx | 1 +
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/src/Time/tide.cxx b/src/Time/tide.cxx
index ce9df6420..b2214b43a 100644
--- a/src/Time/tide.cxx
+++ b/src/Time/tide.cxx
@@ -37,6 +37,8 @@ void FGTide::bind()
SGPropertyNode *props = globals->get_props();
viewLon = props->getNode("sim/current-view/viewer-lon-deg", true);
+ viewLat = props->getNode("sim/current-view/viewer-lat-deg", true);
+
_tideAnimation = props->getNode("/environment/sea/surface/delta-T-tide", true);
_tideLevelNorm = props->getNode("/sim/time/tide-level-norm", true);
@@ -46,6 +48,8 @@ void FGTide::bind()
void FGTide::unbind()
{
viewLon.reset();
+ viewLat.reset();
+
_tideLevelNorm.reset();
_tideAnimation.reset();
}
@@ -56,8 +60,14 @@ void FGTide::update(double dt)
FGLight *l = static_cast<FGLight*>(globals->get_subsystem("lighting"));
// Don't know where the 60 degrees offset comes from but it matches
- // the tides perfectly (at EHAL). Something to figure out.
- double viewer_lon = (viewLon->getDoubleValue() + 60.0)*SGD_PI/180.0;
+ // the tides perfectly at EHAL. Something to figure out.
+ // Eureka: It was the latitude (53.45 degrees north).
+ // It turns out that the moon is draging the tide with an almost
+ // perfect 45 degrees 'bow-wave' along the equator. Tests at SMBQ
+ // (0 degrees latitude) confirmed this finding.
+ double viewer_lon = (viewLon->getDoubleValue()
+ + fabs( viewLat->getDoubleValue() )
+ ) * SGD_DEGREES_TO_RADIANS;
double moon_lon = l->get_moon_lon() - viewer_lon;
if (fabs(_prev_moon_lon - moon_lon) > (SGD_PI/360.0))
{
diff --git a/src/Time/tide.hxx b/src/Time/tide.hxx
index 1874e8549..b90cd0a2c 100644
--- a/src/Time/tide.hxx
+++ b/src/Time/tide.hxx
@@ -54,6 +54,7 @@ private:
double _tide_level = 0;
SGPropertyNode_ptr viewLon;
+ SGPropertyNode_ptr viewLat;
SGPropertyNode_ptr _tideLevelNorm;
SGPropertyNode_ptr _tideAnimation;
};