From 16a54a4409a130b42f02a5f70e18aec5ec6be1c3 Mon Sep 17 00:00:00 2001
From: James Turner <zakalawe@mac.com>
Date: Wed, 26 Oct 2011 17:26:11 +0100
Subject: [PATCH] Change a hot-spot in the AI code, to use cartesian instead of
 geodetic math.

---
 src/AIModel/AIAircraft.cxx | 11 ++++++-----
 src/Main/globals.cxx       |  5 +++++
 src/Main/globals.hxx       |  2 ++
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/AIModel/AIAircraft.cxx b/src/AIModel/AIAircraft.cxx
index a87a94fe6..2722886c6 100644
--- a/src/AIModel/AIAircraft.cxx
+++ b/src/AIModel/AIAircraft.cxx
@@ -838,11 +838,12 @@ bool FGAIAircraft::leadPointReached(FGAIWaypoint* curr) {
 }
 
 
-bool FGAIAircraft::aiTrafficVisible() {
-  SGGeod userPos(SGGeod::fromDeg(fgGetDouble("/position/longitude-deg"), 
-    fgGetDouble("/position/latitude-deg")));
-  
-  return (SGGeodesy::distanceNm(userPos, pos) <= TRAFFICTOAIDISTTODIE);
+bool FGAIAircraft::aiTrafficVisible()
+{
+    SGVec3d cartPos = SGVec3d::fromGeod(pos);
+    const double d2 = (TRAFFICTOAIDISTTODIE * SG_NM_TO_METER) *
+        (TRAFFICTOAIDISTTODIE * SG_NM_TO_METER);
+    return (distSqr(cartPos, globals->get_aircraft_positon_cart()) < d2);
 }
 
 
diff --git a/src/Main/globals.cxx b/src/Main/globals.cxx
index 4d6d7bf57..c4bb125a7 100644
--- a/src/Main/globals.cxx
+++ b/src/Main/globals.cxx
@@ -380,6 +380,11 @@ FGGlobals::get_aircraft_position() const
     throw sg_exception("Can't get aircraft position", "FGGlobals::get_aircraft_position()" );
 }
 
+const SGVec3d&
+FGGlobals::get_aircraft_positon_cart() const
+{
+    return SGVec3d::fromGeod(get_aircraft_position());
+}
 
 
 // Save the current state as the initial state.
diff --git a/src/Main/globals.hxx b/src/Main/globals.hxx
index 54b777a71..365ce3988 100644
--- a/src/Main/globals.hxx
+++ b/src/Main/globals.hxx
@@ -267,6 +267,8 @@ public:
 
     const SGGeod & get_aircraft_position() const;
 
+    const SGVec3d& get_aircraft_positon_cart() const;
+    
     inline FGModelMgr *get_model_mgr () { return model_mgr; }
 
     inline void set_model_mgr (FGModelMgr * mgr)