SphereSensor

Definition :
SphereSensor { 
  exposedField SFBool     autoOffset        TRUE
  exposedField SFBool     enabled           TRUE
  exposedField SFRotation offset            0 1 0 0
  eventOut     SFBool     isActive
  eventOut     SFRotation rotation_changed
  eventOut     SFVec3f    trackPoint_changed
}
Explanation :

The SphereSensor maps pointing device (e.g. mouse or wand) motion into spherical rotation about the center of its local space. SphereSensor uses the descendant geometry of its parent node to determine if a hit occurs. The feel of the rotation is as if you were rolling a ball.

The SphereSensor generates events if the pointing device is activated while over any descendant geometry nodes of its parent group and then moved while activated. Typically, the pointing device is a 2D device such as a mouse. The pointing device is considered to be moving within a plane at a fixed distance from the viewer and perpendicular to the line of sight; this establishes a set of 3D coordinates for the pointer. If a 3D pointer is in use, then the sensor generates events only when the pointer is within the user's field of view. In either case, the pointing device is considered to "pass over" geometry when that geometry is intersected by a line extending from the viewer and passing through the pointer's 3D coordinates. If multiple sensors' geometry intersect this line (hereafter called the bearing), only the nearest will be eligible to generate events.

autoOffset :
enabled :
offset :
isActive :
rotation_changed :
trackPoint_changed :