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private function updateNavigation():void
{
        var rotateX_speed:Number = 0.5;
    var rotateY_speed:Number = 0.5;


    if( lastX == -1 && lastY == -1 )
        {
        lastX = mouseX;
        lastY = mouseY;
    }

    var changeX:Number = lastX - mouseX;
    var changeY:Number = lastY - mouseY;

    lastX = mouseX;
    lastY = mouseY;

    if( navigating )
    {
        rotateX -= changeY * rotateX_speed;
        rotateY += changeX * rotateY_speed;
    }
}