An app for Android phones is now available. Click or scan the image above to install via Google Play.
A book, written by Keith Stevens and Peter Whittaker, about trigpointing walks in the Peaks.
A book, written by Keith Stevens, about trigpointing walks in the Dales.
An e-book, written by John Davies, about the Primary Re-triangulation in Wales.
A book, written by a long standing T:UK member, about trigpoint walks in the Peak District.
Types and classifications of trigpoints
TYPES OF TRIGPOINT
The vast majority of the old triangulation pillars, and most of the FBMs have fallen into disuse. While the Ordnance Survey have a database of their locations, it is not maintained and they have no interest in the current state of repair of individual trigpoints (unless they are a safety risk). A number of groups (eg the Ramblers Association) have "adopted" individual trigpoints and keep them in good repair. Passive stations which have been removed from the network will also fall into this category.
There are currently 163 stations in the active network, located at about 30 sites across Great Britain. These are transmitters which, when used in conjunction with the Rinex data provided by the Ordnance Survey, allow a very high level of positional accuracy to be achieved, without the need to physically occupy one of the Passive Stations.
There are currently 1009 stations in the passive network. These are accurately surveyed locations around the country which, unlike traditional pillars and FBMs, are both easily accessible and give good accuracy for both position and height. An online database of passive stations is maintained by the Ordnance Survey.
Most of the stations in the active and passive network are new and have no prior use.
A set of around 376 triangulation pillars constituted the primary network. These were surveyed between 1936 and 1962 and can be considered the "backbone" of the triangulation network.
A set of around 2289 triangulation pillars constituted the secondary network. These "filled in the gaps" between the primary stations.
An underground chamber topped with a short granite pillar. The pillar contains an easily accessible height reference point, but the accurately measured level is underground where it is less likely to be disturbed. There are approximately 207 FBMs across the country and these provided the primary layer of the "Ordnance Datum Newlyn". Levelling between these locations provided accurate height information, though the horizontal location was less well determined than for the triangulation pillars.
Decommissioned active stations (see above).
Decomissioned passive stations (see above).
You may have noticed that some of the figures given above are inconsistent. This is because the data held in this database is incomplete and often self contradictory. For example, the number FBMs in the country is quoted as being 207, whereas the number of trigpoints whose historic use was as a FBM is 207. This does not sit well with the assumption that no new FBMs have recently been built, eg for the passive network. It is hoped that as people log their finds on this site, we will in time build up a better picture of what's out there, and "clean up" the data in the database.