Nielsen is desperately trying to re-assert itself as the leader in TV viewing measurement in the digital era, despite others in the space, like comScore, gaining favor among TV networks for its ability to measure online viewers. Nielsen hopes to demonstrate its ability to measure audiences outside the living room, quite literally by unveiling its new out of home TV viewership service. Nielsen first announced it was working on a national out of home ratings service late last year. ESPN and Turner are the first networks to use the service, which measures viewing that occurs in places like bars, hotels, doctor’s offices, gyms and other public places. Nielsen said it’ll include out of home data in all its sports viewership…