Curious rotating device on London Underground

Hi all, this is a real long shot as I've only got a vague description from memory, but can anyone help me identify this device?

It was probably 15-20 years ago and I want to say it was a Circle line station where I saw it, but I can't remember which station and it might not even have been the Circle!

At one far end of the rails, just before they disappeared into the tunnel, and clearly visible from the platform, was a device about four feet high which seemed to be a camera of some sort. It was pointing along the rails in the direction that the trains came in to the station, but every 20 seconds or so it would perform a weird sort of rotation, where the camera turned around 180 degrees but the whole assembly seemed to up-end itself so that a second camera was now pointing along the rails. Then, about 20 seconds later, it would perform this action again so that the first camera had a view of the rails. This kept repeating over and over.

Does anyone have the faintest idea what I'm describing? I'm absolutely certain I didn't imagine it but that's pretty much all I can remember about it!

Surveying equipment? To detect movement in the tunnels whilst work (eg Crossrail) is being done nearby.

from Geoff Marshall.

It would be an automatic (robotic) surveying device (I think called a “total station”). Basically it’s an automated theodolite checking for subsistence or movement caused by nearby work. They aim at laser targets fixed all over the place.

Thanks both! That definitely sounds like what it could have been -- now that I've got your suggestions I can do a bit more reading up; all these years I've wondered what on earth it was and all I needed to do was ask! Thanks again for your help

Jgc1457 said:

Thanks both! That definitely sounds like what it could have been -- now that I've got your suggestions I can do a bit more reading up; all these years I've wondered what on earth it was and all I needed to do was ask! Thanks again for your help

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No problem, and welcome to these forums.

swt_passenger said:

No problem, and welcome to these forums.

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Thank you, swt_passenger

There's a couple currently installed in the ceiling of the southbound Northern line platform tunnel at Bank which are presumably to monitor ground movement whilst they're digging the new platform tunnel adjacent (they've installed doors through the wall opposite the platform that presumably lead into the construction site - it's a slightly odd looking affair.)

If it was the circle line about 20 years ago, was probably Westminster
From memory as the Jubilee line station was built underneath the track, it was gradually transferred to new beams, about 2m at a time on various weekends.

wouldn’t have been Crossrail as digging for that in Central London didn’t really get going until 2009 or 2010

These devices (normally coloured green for some reason) are often a fascination for passing members of the public when they come to their attention, performing a seemingly bizarre series of gyrations. They do indeed look and act like something out of Doctor Who spying on who is around. I think they got their big break from the collapse of the Heathrow Express tunnel in the airport, which could have been detected by small ground movements well before it was noticed it was falling in. There's been a lot of research done in California etc to using the technique for advance prediction of earthquakes by detecting prior imperceptable ground movements.

That's what they want you to believe. In reality they are the vanguard of an alien invasion. They are infiltrating key infrastructure projects to try to slip in unnoticed, but there are those of us who intend to rise up against the 'visitors' and expose their evil plan. Little Green Gyrating Men beware!

Yes - welcome to the forums!

I've seen reflectors on walls of escalators too.
The camera at the top when in motion seems to be on a mission and people think it's CCTV.