From 1f4371245b410162238c625db718e993e2ab7bf4 Mon Sep 17 00:00:00 2001
From: "Curtis L. Olson" <curtolson@gmail.com>
Date: Tue, 18 Jan 2011 11:47:15 -0600
Subject: [PATCH] Address Melchior's concern about view prediction depending on
 a particular aircraft system, rather than "core" data.

Fix a long standing annoyance (for me anyway) when the fly-by-view is first
instantiated, it never put a point forward very far so the first transtion
came very quickly and abruptly.  Improve the forward prediction based on
ground speed and time when the view is reset (or switched to.)  I like this
a lot better personally.
---
 Nasal/view.nas | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/Nasal/view.nas b/Nasal/view.nas
index acc0c346d..f94ae02b5 100644
--- a/Nasal/view.nas
+++ b/Nasal/view.nas
@@ -252,8 +252,9 @@ var fly_by_view_handler = {
 		me.latN = props.globals.getNode("/sim/viewer/latitude-deg", 1);
 		me.lonN = props.globals.getNode("/sim/viewer/longitude-deg", 1);
 		me.altN = props.globals.getNode("/sim/viewer/altitude-ft", 1);
-		# me.hdgN = props.globals.getNode("/orientation/heading-deg", 1);
-		me.hdgN = props.globals.getNode("/instrumentation/gps/indicated-track-true-deg", 1);
+		me.vnN = props.globals.getNode("/velocities/speed-north-fps", 1);
+		me.veN = props.globals.getNode("/velocities/speed-east-fps", 1);
+		me.hdgN = props.globals.getNode("/orientation/heading-deg", 1);
 
 		setlistener("/sim/signals/reinit", func(n) { n.getValue() or me.reset() });
 		setlistener("/sim/crashed", func(n) { n.getValue() and me.reset() });
@@ -267,21 +268,37 @@ var fly_by_view_handler = {
 	},
 	reset: func {
 		me.chase = -getprop("/sim/chase-distance-m");
-		me.course = me.hdgN.getValue();
+		# me.course = me.hdgN.getValue();
+		var vn = me.vnN.getValue();
+		var ve = me.veN.getValue();
+		me.course = (0.5*math.pi - math.atan2(vn, ve))*R2D;
+		
 		me.last = geo.aircraft_position();
 		me.setpos(1);
-		me.dist = 20;
+		# me.dist = 20;
 	},
 	setpos : func(force = 0) {
 		var pos = geo.aircraft_position();
+		var vn = me.vnN.getValue();
+		var ve = me.veN.getValue();
+
+		var dist = 0.0;
+		if ( force ) {
+		    # predict distance based on speed
+		    var mps = math.sqrt( vn*vn + ve*ve ) * FT2M;
+		    dist = mps * 3.5; # 3.5 seconds worth of travel
+		} else {
+		    # use actual distance
+		    dist = me.last.distance_to(pos);
+		}
 
 		# check if the aircraft has moved enough
-		var dist = me.last.distance_to(pos);
 		if (dist < 1.7 * me.chase and !force)
 			return 1.13;
 
 		# "predict" and remember next aircraft position
-		var course = me.hdgN.getValue();
+		# var course = me.hdgN.getValue();
+		var course = (0.5*math.pi - math.atan2(vn, ve))*R2D;
 		var delta_alt = (pos.alt() - me.last.alt()) * 0.5;
 		pos.apply_course_distance(course, dist * 0.8);
 		pos.set_alt(pos.alt() + delta_alt);