Any question answered...

I'm currently working near Paddington basin and and I've noticed what look like mirrored orange reflectors over a lot of bolts on semi permanent structures along the canal. Anyone know the purpose of these? Can't say if I've ever noticed them anywhere else, I've never really looked!

I live a block away. They have to do with measuring ground shifts as they are tunneling underneath for the Cross Rail.
I asked, as they are on a lot of houses in da hood.