The problem of controlling a group of agents to achieve a desired geometric formation is considered. We provide sufficient conditions under which agents autonomously achieve any feasible desired formation, while the sensing topology among them can change arbitrarily. The desired formation is defined in terms of inter-agent distances and angles. Agents do not need to have a common or global coordinate frame, and local relative position measurements of their neighbors suffices to achieve the desired formation. Stability analysis, illustrative examples, and simulation results are provided.