This paper describes a GNSS (Global Navigation Satellite System) precise point positioning (PPP) technique that can be applied to mobile robots in urban environments. The multipath signals, which from invisible satellites in urban area, cause serious effect on the GNSS positioning. Our proposed technique mitigates GNSS multipath signals by means of an omnidirectional infrared (IR) camera that can eliminate the need for invisible satellites by using IR images. With an IR camera, the sky appears distinctively dark. This facilitates the detection of the borderline between the sky and the surrounding buildings, which are captured in white, because of the difference in the atmospheric transmittance rates between visible light and IR rays. Positioning evaluation was carried out only with visible satellites that have less multipath errors. The evaluation results confirm the effectiveness of the proposed technique and the feasibility of its highly accurate positioning.