From 6fe084df3b089835a850578628b3f7128cc2b001 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Mon, 14 Jun 2010 16:27:35 +0000
Subject: [PATCH] Introduced the use of atan2 in place of asin/acos for
 reliability and simplicity

---
 src/osgSim/SphereSegment.cpp | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/osgSim/SphereSegment.cpp b/src/osgSim/SphereSegment.cpp
index 77d4c4223..1ad5c2a57 100644
--- a/src/osgSim/SphereSegment.cpp
+++ b/src/osgSim/SphereSegment.cpp
@@ -289,16 +289,15 @@ void SphereSegment::setArea(const osg::Vec3& v, float azRange, float elevRange)
     vec.normalize();    // Make sure we're unit length
 
     // Calculate the elevation range
-    float elev = asin(vec.z());   // Elevation angle
+    float xyLen = sqrtf(vec.x()*vec.x() + vec.y()*vec.y());
+    float elev = atan2(vec.z(), xyLen);   // Elevation angle
+
     elevRange /= 2.0f;
     _elevMin = elev - elevRange;
     _elevMax = elev + elevRange;
 
-    // Calculate the azimuth range, cater for trig ambiguities
-    float xyLen = cos(elev);
-    float az;
-    if(vec.x() != 0.0f) az = asin(vec.x()/xyLen);
-    else az = acos(vec.y()/xyLen);
+    // Calculate the azimuth range, cater for trig ambiguities    
+    float az = atan2(vec.x(), vec.y());
 
     azRange /= 2.0f;
     _azMin = az - azRange;