The love of railway bridges

I was competeing in a fishing match beside this railway bridge today when a man with a rucksack walked up to it and started taking lots of photographs from every angle he could get think of.
I said hello but he didn't reply so I thought oh dear here I am the wrong side of the railway bridge away from all my fishing club colleagues and here is a man who so loves the railway bridges perhaps too much !!!
Imagine my shock when he took out a device and started pointing and clicking at points all over the bridge, he then took out an A4 book and started writing and drawing. He stayed for an hour and a half then walked away back where he had come from. Weird!