This paper summarizes the work done on the development of a module to interface a commercial mechanical scan sonar within an ROV control architecture and its integration with the other modules. The sonar module fulfills the scope of endowing the ROV with an open tool for the management of the sonar setting, adapting sonar performances to the specific mission requirement. In particular, this work is focused on the problem of the generation of environmental map from raw sonar scan data for objects detection purposes as well as for ROV self localization means. Preliminary assumption on the ROV motion ensures the construction of two-dimensional maps of the environment. Additionally, a procedure for self localization of the ROV based on sonar map and on onboard compass data is developed. Experimental tests on structured environment have been performed and other are planned in order to test the validity of the proposed solution. The research has been partially sponsored by the national project PICTURE