BrownhillsBob's #365daysofbiking

On a bike, riding somewhere. Every day, rain or shine.

Posts tagged ‘datum’

#365daysofbiking Feeling flush

 

 

March 11th – I had time to spare so hopped onto the restored canal at Droitwich for a mooch. Just under the railway bridges in the last entry, I noticed this relic of the Ordnance Survey.

Flush Bracket 480 is one of a range of such brackets intended as mapmaker’s datums, the slots in which were for mounting surveying equipment at a known datum – in this case 28.7490m above sea level (the Newlyn Datum).

Now redundant as cartographer’s aids, these are more a historical curiosity than anything else, but I still get a buzz from spotting them in the wild.

You can find out more about this one here.

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January 16th – As much as I’m growing to loathe the results of the renovation of New Street Station in Birmingham, the process is still fascinating me. One of the things I like about it is how normal conventions of public buildings are broken. There is serious civil engineering going on at the same time as huge numbers of people and trains pass through this humming interchange..

Odd things happen.

Personnel appear from hidden doorways and gaps. There are odd noises and bangs. Occasionally, you get sprayed with water, or dust. Lifts and stairs appear, and then are boarded up again. cables dangle and tangle above the headspaces, and snake and race through the girders and scaffold.

One of the things you see here you don’t elsewhere is engineering graffiti. Surveyors measure. Sparkies test. Cladders clad. All of them leave their marks and datums scribbled on walls, floors and hoardings. Sometimes, they make sense. Often, they’re just mysterious glyphs, whose purpose is only known to those with the skill. I love how they ebb and flow with the focus of the work.

Spotting them is something to do while you wait…

August 18th – Chasewater is great at the moment. I passed through in the early afternoon, on a warm but windy Sunday; the lake was busy, and people were out, taking the air, cycling, walking dogs, playing football or frisby with their kids. So nice to see it busy and beautiful again.

I see the herd of cattle has expanded – as well as the lads munching away on the north heath, we now have a bovine maintenance crew on the spillway heath, between the Nine-Foot, Anglesey Basin and the Toll Road boundary. Like cows do, they were exploring the field boundaries and watching passers by nosily. They’re a great asset to Chasewater and it’s good to see them.

Meanwhile, on the embankment track between Jeffrey’s Swag and Slurry Pool, someone has been measuring. That’s a surveyor’s datum block (the stud is the datum) and presumably that’s some kind of measurement bore. Wonder what they’re looking at?

January 28th – Birmingham New Street Station is undergoing huge alterations at the moment, and is overrun buy people involved in the reconstruction. Sometimes, they almost seem to match in number the passengers; they emerge from hatches and previously unnoticed doorways, often surveying, taking measurements or gazing at ceilings. There’s clearly a lot of thought going on.

I keep noticing these tiny target symbols in odd locations about the station. About 20mm square, they have a precision cross-hair on them and a unique number , and they’re printed on reflective material. They’re vital to operations here, but I suspect few ever notice them.

They’re measurement datums. A theodolite – either placed in position by an engineer, or permanently sited in an out of the way spot – will focus on this target, and accurate geometrical measurements can be made, indicating if the target, or the wall it’s attached to, has moved, or to precisely locate some other measurement. Automatic systems will do this across multiple visible datums repeatedly, unattended, and alert engineers if there’s any change.

I suspect this is part of an automatic monitoring system as it’s above normal working, and therefore, crowd height, just to the left of the telephone kiosk roof.

Civil engineering is getting more and more sophisticated.