A mobile device includes a rangefinder to measure ranges to points external to the device; a tracking sensor; and a controller connected with the rangefinder and the tracking sensor, the controller configured to: track successive poses of the mobile device in a frame of reference via the tracking sensor; responsive to a first activation of the rangefinder at a first one of the poses, generate a first position, in the frame of reference, of a first external point based on a first range from the rangefinder and the first pose; responsive to a second activation of the rangefinder at a second one of the poses, generate a second position, in the frame of reference, of a second external point based on a second range from the rangefinder and the second pose; and determine a distance between the first and second external points based on the first and second positions.