1. A system for stereotactic positioning in real time of a first object relative to a second object, the first object having a tip, the system comprising: a. at least four transmitting units (TUs) arranged spatially such that no more than three TUs are coplanar, each TU including at least one ultrasound (US) transmitter, a radio frequency (RF) transmitter and a TU clock, wherein at least one TU includes two US transmitters that transmit on two different frequencies f 1 and f 2 ; b. a mobile unit (MU) fixedly coupled to the first object, the MU including a MU clock, a RF transmitter/receiver and two US receivers spaced apart and positioned in a predetermined geometrical relation relative to the first object tip, wherein one receiver is adapted to receive US transmissions on frequency f 1 and wherein the other receiver is adapted to receive US transmissions on frequency f 2 ; and c. a central processing unit (CPU) configured to determine a real space position of the first object tip based on US time-of-flight (TOF) data obtained from ultrasound transmissions between each US transmitter and each US receiver and to display simultaneously the real space tip position together with reconstructed image space data of the second object.