Trig point visibility

[Neda Archi]

Hello!

I am an architecture student and my current project involves analysis and interventions regarding trig points in the UK.
I wanted to ask you - I have read that there must be a direct line of sight from one trig point to another. Does that mean that a single trig point must be able to "See" all trig points visible from that point (like in the image I linked below), or just the closest ones/ etc?

Thank you so much for your help!

https://64.media.tumblr.com/5a5fe547c7a ... c95c8e.jpg

[TrigJS]

A trig point would need to able to observe (or be observed by in the case of intersected trig points) at least two other trig points in order to make a triangle. Of course there are exceptions to this especially if you have other observations you can add to the computational mix (e.g. distances). In reality you’d want to be able to observe angles to more than two other trig points in order to provide observational redundancy.

There was a scan of a book called “The History of the Retriangulation of Great Britain” that was free to download from the Ordnance Survey website. Not sure if it’s still there and if you can find it you may find it helpful reading.

[Neda Archi]

A trig point would need to able to observe (or be observed by in the case of intersected trig points) at least two other trig points in order to make a triangle. Of course there are exceptions to this especially if you have other observations you can add to the computational mix (e.g. distances). In reality you’d want to be able to observe angles to more than two other trig points in order to provide observational redundancy.

There was a scan of a book called “The History of the Retriangulation of Great Britain” that was free to download from the Ordnance Survey website. Not sure if it’s still there and if you can find it you may find it helpful reading.

Thank you so much for your response!
I have one additional question - I am looking into a specific trig point that is classified as "secondary". Would that point need to have a visual relationship with other secondary points only or does this classification not matter in this case?
Once again, I am grateful for your response!

[TrigJS]

This link will provide more detail -

http://trigpointing.uk/wiki/Order

Secondary trig points would be able to observe some primary TPs as well other secondary, tertiary and fourth order TPs.

[Neda Archi]

This link will provide more detail -

http://trigpointing.uk/wiki/Order

Secondary trig points would be able to observe some primary TPs as well other secondary, tertiary and fourth order TPs.

That is really helpful, thank you so much!:)

[wheresthatpenguin]

A trig point would need to able to observe (or be observed by in the case of intersected trig points) at least two other trig points in order to make a triangle. Of course there are exceptions to this especially if you have other observations you can add to the computational mix (e.g. distances). In reality you’d want to be able to observe angles to more than two other trig points in order to provide observational redundancy.

There was a scan of a book called “The History of the Retriangulation of Great Britain” that was free to download from the Ordnance Survey website. Not sure if it’s still there and if you can find it you may find it helpful reading.

Whilst “The History of the Retriangulation of Great Britain” is no longer available as a free download, there are people out there who produce facsimile copies printed to order, which is how I got my copy.

[Teasel]

I commissioned a searchable scan of "The History of the Retriangulation of Great Britain" shortly before its Crown Copyright expired. It can be downloaded from here: https://storage.googleapis.com/retriang ... 5-1962.pdf

The diagrams in the appendix show the complete set of primary observations, plus some examples of higher order observations:
https://storage.googleapis.com/retriang ... agrams.zip

[ted]

I commissioned a searchable scan of "The History of the Retriangulation of Great Britain"

Thanks! The photos of trig construction and surveyors at work are fascinating.

Ted

[ted]

> Postby Teasel » Sat Aug 13, 2022 9:24 pm
> I commissioned a searchable scan of "The History of the Retriangulation of Great Britain" shortly before its Crown Copyright expired.
> It can be downloaded from here: https://storage.googleapis.com/retriang ... 5-1962.pdf

I'm slightly confused about the status of the Retriangulation book on the trig wiki.
Page 19 is available: https://trigpointing.uk/wiki/Book:Retriangulation/p19
But a test of a few other pages responds with a 'page empty' message.

Now that the book is out of copyright, are there any plans to make it fully available on the wiki?
I'd like to cite a few particular pages from other trig wiki topics.

Alternatively, if the google URL is stable, I could reference it with #page=[page number] added
but that seems a bit inelegant.


Thanks
Ted