Techniques for enhanced Global Navigation Satellite Systems (GNSS) position determination can include capturing an image, from a camera, of obstructions near a mobile device. Orientation information regarding the camera can is used to determine where, in the image, the horizon is situated, and which portions of the sky are blocked by the obstructions from the perspective of the mobile device. Information regarding the location of satellites in the sky is obtained, based on an estimated position of the mobile device. Obstructed satellites can then be identified by comparing the location of the satellites with the obstructed portions of the sky. In a GNSS position determination, information received from the obstructed satellites can then be disregarded or de-weighted accordingly. In some embodiments, the information regarding the blocked portions of the sky can be sent to a server and/or shared with other nearby mobile devices.