Obstacles in Vehicular ad hoc networks (VANETs) in urban scenarios are an important issue. Normally, in traffic simulators vehicles can send/receive packets between each other if they are in the same transmission range no matter if an obstacle is presented or not between them. For this reason, checking if there is an obstacle between sender and receiver is an important goal. In this paper, we present a program named REVsim1.0 (Realistic Environment for Vanets simulation) [1] capable to detect at each instant of time if between a sender and a receiver a communication can be established or conversely, if an obstacle is found and such a communication is not possible. Parameters such as a, ß, road resolution and transmission range have been defined and used in our proposed algorithm. Finally, a validation of our algorithm is shown.