Trig Points

[simon.r]

I normally whiz past (all things being relative) this trig point which isn't far from me, but I'm recovering from man-flu and this morning's ride was a struggle, so I stopped to look at it:

Apparently these are now disappearing http://en.wikipedia.org/wiki/Trig_point#United_Kingdom as digital mapping takes over.

Just thought I'd share

 

[Deleted member 23692]

If you're within 10ft of a trig point, your sandwiches taste better

 

[Cubist]

Useful things to prop your bike up against too....

 

[Globalti]

Can any surveyor explain the purpose of the slots and the eyes? My guess was always that they provided a stable anchorage for a theodolite, am I right?

 

[Deleted member 23692]

Can any surveyor explain the purpose of the slots and the eyes? My guess was always that they provided a stable anchorage for a theodolite, am I right?

Correct, and here's a photo of an OS survey team .... surveying

 

[ColinJ]

A repeat of an interesting TV series called Map Man|/i] has been showing for a few weeks now. It features Nicholas Crane out and about, talking about old maps and mapping techniques. You can probably catch some of the programmes on iPlayer.

In one programme, Crane took some old surveying equipment to the top of some hills and demonstrated the triangulation technique. It amazed me that they used to start from a base line measured using a metal tape, and all the other measurements were relative to that and calculated by triangulation.

 

[Deleted member 23692]

He's a curio I picked up on my travels...

It's quite hefty... and needs a polish!

 

[MontyVeda]

They should be listed 'buildings'.

 

[Deleted member 23692]

Some trig facts...

1. The survey control network of trig pillars was accurate to 20 metres over the entire length of Great Britain. Today the receivers that make up the OS Net network are coordinated to an accuracy of just 3 mm over the same area.

2. Starting in 1936, 6,500 trig pillars were built for the retriangulation of which around 5,500 are still standing. In total the retriangulation had in excess of 30,000 coordinated points. The modern OS Net network performs the same function with just 110 points.

3. Measuring angles by eye from a trig pillar meant the retriangulation was reliant on good weather – perhaps part of the reason it took until 1962 to complete! Modern GNSS surveying works in all weathers and is available 24 hours a day.

4. Trig pillars are mostly made of cast concrete but a few are built from local stone cemented together.

5. Like an iceberg, there is more of trig pillar below the surface than above it.

 

[neil_merseyside]

The middle circular bit screws out with a two pin wrench to expose a mounting thread for survey instrument, brass channels are for tripod legs to enable fine adjustment apparently. This is gospel from my scout master <mumble> years ago. Occasionally a trig point will supposedly coincide with a channel (allegedly, they are always miles away to really know!) but any coastal trig point proves that to be false!

 

[captain nemo1701]

Useful things to prop your bike up against too....

Is that the one at Beacon Batch on the Mendips, near the two transmitter masts?

 

[ColinJ]

Is that the one at Beacon Batch on the Mendips, near the two transmitter masts?

It looks like High Brown Knoll on Oxenhope Moor to me!

 

[Cubist]

Is that the one at Beacon Batch on the Mendips, near the two transmitter masts?

Not quite......

It looks like High Brown Knoll on Oxenhope Moor to me!

Its neighbour, Norland Moor.

 

[Cubist]

Not quite......


Its neighbour, Norland Moor.

Just checked landranger, they're almost in a line N to S. There's a higher hill , getting on for 150m higher, Nab Hill, Ovenden Moor between them.

 

[ColinJ]

Just checked landranger, they're almost in a line N to S. There's a higher hill , getting on for 150m higher, Nab Hill, Ovenden Moor between them.

The trig point I was thinking of is SW of Nab Hill, at SE 009 304. (Sorry - it's Midgley Moor, not nearby Oxenhope Moor.)