diff --git a/apps/openmw/mwphysics/trace.cpp b/apps/openmw/mwphysics/trace.cpp
index 57b0a83680..13bc7f7983 100644
--- a/apps/openmw/mwphysics/trace.cpp
+++ b/apps/openmw/mwphysics/trace.cpp
@@ -14,9 +14,9 @@ namespace MWPhysics
 class ClosestNotMeConvexResultCallback : public btCollisionWorld::ClosestConvexResultCallback
 {
 public:
-    ClosestNotMeConvexResultCallback(const btCollisionObject *me, const btVector3 &up, btScalar minSlopeDot)
+    ClosestNotMeConvexResultCallback(const btCollisionObject *me, const btVector3 &motion, btScalar minCollisionDot)
       : btCollisionWorld::ClosestConvexResultCallback(btVector3(0.0, 0.0, 0.0), btVector3(0.0, 0.0, 0.0)),
-        mMe(me), mUp(up), mMinSlopeDot(minSlopeDot)
+        mMe(me), mMotion(motion), mMinCollisionDot(minCollisionDot)
     {
     }
 
@@ -34,8 +34,9 @@ public:
             hitNormalWorld = convexResult.m_hitCollisionObject->getWorldTransform().getBasis()*convexResult.m_hitNormalLocal;
         }
 
-        btScalar dotUp = mUp.dot(hitNormalWorld);
-        if(dotUp < mMinSlopeDot)
+        // dot product of the motion vector against the collision contact normal
+        btScalar dotCollision = mMotion.dot(hitNormalWorld);
+        if(dotCollision <= mMinCollisionDot)
             return btScalar(1);
 
         return ClosestConvexResultCallback::addSingleResult(convexResult, normalInWorldSpace);
@@ -43,8 +44,8 @@ public:
 
 protected:
     const btCollisionObject *mMe;
-    const btVector3 mUp;
-    const btScalar mMinSlopeDot;
+    const btVector3 mMotion;
+    const btScalar mMinCollisionDot;
 };
 
 
@@ -59,22 +60,21 @@ void ActorTracer::doTrace(const btCollisionObject *actor, const osg::Vec3f& star
     from.setOrigin(btstart);
     to.setOrigin(btend);
 
-    ClosestNotMeConvexResultCallback newTraceCallback(actor, btstart-btend, btScalar(0.0));
+    const btVector3 motion = btstart-btend;
+    ClosestNotMeConvexResultCallback newTraceCallback(actor, motion, btScalar(0.0));
     // Inherit the actor's collision group and mask
     newTraceCallback.m_collisionFilterGroup = actor->getBroadphaseHandle()->m_collisionFilterGroup;
     newTraceCallback.m_collisionFilterMask = actor->getBroadphaseHandle()->m_collisionFilterMask;
 
     const btCollisionShape *shape = actor->getCollisionShape();
     assert(shape->isConvex());
-    world->convexSweepTest(static_cast<const btConvexShape*>(shape),
-                                               from, to, newTraceCallback);
+    world->convexSweepTest(static_cast<const btConvexShape*>(shape), from, to, newTraceCallback);
 
     // Copy the hit data over to our trace results struct:
     if(newTraceCallback.hasHit())
     {
-        const btVector3& tracehitnormal = newTraceCallback.m_hitNormalWorld;
         mFraction = newTraceCallback.m_closestHitFraction;
-        mPlaneNormal = osg::Vec3f(tracehitnormal.x(), tracehitnormal.y(), tracehitnormal.z());
+        mPlaneNormal = Misc::Convert::toOsg(newTraceCallback.m_hitNormalWorld);
         mEndPos = (end-start)*mFraction + start;
         mHitPoint = Misc::Convert::toOsg(newTraceCallback.m_hitPointWorld);
         mHitObject = newTraceCallback.m_hitCollisionObject;
@@ -91,14 +91,15 @@ void ActorTracer::doTrace(const btCollisionObject *actor, const osg::Vec3f& star
 
 void ActorTracer::findGround(const Actor* actor, const osg::Vec3f& start, const osg::Vec3f& end, const btCollisionWorld* world)
 {
-    const btVector3 btstart(start.x(), start.y(), start.z());
-    const btVector3 btend(end.x(), end.y(), end.z());
+    const btVector3 btstart = Misc::Convert::toBullet(start);
+    const btVector3 btend = Misc::Convert::toBullet(end);
 
     const btTransform &trans = actor->getCollisionObject()->getWorldTransform();
     btTransform from(trans.getBasis(), btstart);
     btTransform to(trans.getBasis(), btend);
 
-    ClosestNotMeConvexResultCallback newTraceCallback(actor->getCollisionObject(), btstart-btend, btScalar(0.0));
+    const btVector3 motion = btstart-btend;
+    ClosestNotMeConvexResultCallback newTraceCallback(actor->getCollisionObject(), motion, btScalar(0.0));
     // Inherit the actor's collision group and mask
     newTraceCallback.m_collisionFilterGroup = actor->getCollisionObject()->getBroadphaseHandle()->m_collisionFilterGroup;
     newTraceCallback.m_collisionFilterMask = actor->getCollisionObject()->getBroadphaseHandle()->m_collisionFilterMask;
@@ -107,9 +108,8 @@ void ActorTracer::findGround(const Actor* actor, const osg::Vec3f& start, const
     world->convexSweepTest(actor->getConvexShape(), from, to, newTraceCallback);
     if(newTraceCallback.hasHit())
     {
-        const btVector3& tracehitnormal = newTraceCallback.m_hitNormalWorld;
         mFraction = newTraceCallback.m_closestHitFraction;
-        mPlaneNormal = osg::Vec3f(tracehitnormal.x(), tracehitnormal.y(), tracehitnormal.z());
+        mPlaneNormal = Misc::Convert::toOsg(newTraceCallback.m_hitNormalWorld);
         mEndPos = (end-start)*mFraction + start;
     }
     else