Abstract: In a method, the light beams of two separated optical radar units (each of which are capable of emitting light pulses in a direction and receiving light pulses from the same direction) are directed to a point. The first optical radar unit emits a light pulse to the point and the second optical radar unit detects the light pulse reflected from the object at the point. After a time interval, the second optical radar unit emits a light pulse to the point and the first optical radar unit detects the light pulse reflected from the object at the point. If there is an object at the point, the time difference of the two detected signals from the two optical radar units is the switching time interval. By comparing the two detected signals from the two optical radar units, one can determine whether an object is at the point.