In a trade show, an exhibition or a similar environment, in order to help participants to get the most out of the visit, there are usually some electronic tour-guide (purchase guide) systems provided which allow users to browse or hear more information of an object they are interest in through a portable client device. Based on the way these systems decide of which object the user is interest in, generally they can be divided into two types. In the first type of systems, the user should manually key in the identification (ID) of the object he/she is interest in on his/her client device. However, this is quite troublesome for users. The second type of systems is the so-called location-based system, where some kind of location detection mechanism (such as radio frequency identification (RFID)) is used, and the client device will automatically deliver the information of an object to the user when the user is standing approximate to this object. Although this type of system is more convenient than the first one, it has following drawbacks. First, when there are several objects with same or similar distance and directional angle to the user, there is no reliable way to decide which object should be the one the user is interested in. Second, after all, the location approximation has no certain relation with a user's real interest. For example, when the user is facing and looking at a picture hanged on the wall several steps away while there is another exhibited item just next to the user's side, in this case, the object closest to the user is not the one the user is actually interested in. So, the object information delivered to the user by a location-based system is not the information of the object the user is actually interested in.