Lasers On A Train

On Wednesday I was waiting in Sheffield station for my train home from work when this Netwrok Rail maintenance train trundled through. Normally the maintenance trains aren't particularly interesting to me (they are after all diesel powered) but the number of laser warning labels stuck to this one caught my eye.

Apparently it's an optical structure gauging train, which I'm guessing means it uses lasers to check that the rails are still in the right place!