GPS  is  used to track  the   object  location  . In GPS system the  satellites  sent  radio waves   and  the  user  segment  captured it  and decode it  and gives location of object  . They are spaced 60 degrees apart and are inclined at about fifty-five degrees with respect to the equator.  In this configuration at least four satellites are available from any location on the earth’s surface at all times. GPS receivers convert SV signal into position, velocity and time estimates.  This process requires four satellites to compute the four dimension.