Please click HERE for the introduction page and latest update information.
| OS Trig Points
OSBM was started in October 2002 as a one member site with the intention of displaying images of a few Ordnance Survey triangulation pillars and several of the different types of flush brackets used on them. Also included were some different types of flush brackets not used on pillars but mounted on fixed structures such as buildings and bridges for the network of Geodetic and Secondary and levelling lines.
OSBM has since attracted the interests of over a hundred like minded people, many of whom have become members, uploading images of their own. OSBM now contains over 1700 pictures of Ordnance Survey Triangulation Pillars, more familiarly known as Trig Points. Most of these images are montages which show also a close up photograph of the uniquely numbered Flush Bracket.
TRIG PILLARS |
Over 6500 triangulation pillars were erected by the Ordnance Survey of Great Britain. Referred to as trig points, these monuments to map making are often found at or near the summits of hills. The triangulation pillars were built for the Retriangulation in Great Britain of 1936-62 and were constructed from 1935 to 1960. Since 1960 some pillars have been rebuilt, repaired or relocated, the last pillars built were built in 1986 for the Channel Tunnel. Click HERE to learn more about how the pillars were built.
Over 6000 of these pillars still stand today. Of the minority which have been lost, the most common causes of loss are quarrying, mining, road building, urban sprawl, vandalism, and modern intensive farming practices. Some clifftop pillars have been lost in landslides.
Some of the captions to these photographs contain historic information about individual pillars such as order (rank), when it was built, and which Secondary Block it was part of. Lists of Secondary Blocks and when individual pillar were built can be found HERE.
LEVELLING LINES
Also on this site are over 3300 photographs of wall mounted non pillar flush brackets (NPFB) which act as Bench Marks along Levelling Lines between Fundamental Bench Marks (FBM). The images of Flush Brackets used on the Geodetic and Secondary levelling lines are all arranged in one album. Some of the photographs are a close up shot of the flush bracket only, others are montages showing the structures the FBs are mounted on alongside the FB itself. Please Click HERE to view the photographs of the NPFBs and their environments. Note the NPFB folder of photographs on OSBM is now archived.
From Jan 2007, all NPFB images should have been posted to http://groups.msn.com/OSBM4
This new group has been created to allow different ranges of NPFBs to be displayed in separate albums.
The aim here is for quantity rather than quality. Whilst every effort is made to visit on days with good weather, you will see from some of the photographs that this does not always work out.
Conditions of Membership and how to be accepted as a new member of OSBM can be found HERE.
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The albums are arranged in order of Flush Bracket number, by the thousand. Please CLICK HERE to see the list of albums. The early unprefixed 2900 series pillars have been grouped with the S2000 series. Click on any of the links listed below to access the images which are grouped by their FB numbers in thousands.
A regularly updated spreadsheet indexing all the trig pillar photographs on this site is in the Index folder . Site membership required to access and download these files.
Official OS Station names and correct Grid References are used to identify triangulation pillars. Many of the locations to be shown are well known. Others may be unheard of. Official OS names all for the OSGB triangulation stations can be found at http://www.36haroldstreet.freeserve.co.uk/trigpoints.htm
| Flush Brackets.
Ordnance Survey flush brackets are probably first noticed on Triangulation pillars. In actual fact there are many more flush brackets on walls, bridges and other fixed structures than there are on triangulation pillars.
There are four known series of flush brackets. The oldest series were manufactured for use on the Second Geodetic levelling of England and Wales 1912-21. There are 3000 of these flush brackets, numbered from 1 to 3000 with no prefix letter. Not all of them were used for their intended purpose, around fifty brackets, all in the 2900s, were placed on the earliest triangulation pillars in 1935/36.
From 1920, numbered flush brackets were also being used for secondary level bench marks. These were distinguishable from the original Geodetic flush brackets with the inclusion of a letter 'S'. This letter 'S' was below the number on the first 1134 of these flush brackets. Those numbered below 1000 were also prefixed with a '0'. An unspoiled example is S0206. From S1135 onwards the 'S' was to the left of the number as shown on S1195. In 1935 when triangulation pillar construction commenced, many of these Secondary flush levelling brackets were used in the pillars. The primary station triangulation pillar on Dunrig has flush bracket S1571. From S3200 to S3677 the 'S' was above the number, but with the exception of S3688/89 the 'S' reverted to the left of the number up to S9999. From 10000 onwards, the 'S' was not used, probably not required as it was known the none of the Geodetic series ranges would reach 10000. Flush Bracket 11415 is on a road bridge in Roxburghshire.
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Comments and suggestions on OSBM are welcome and can be sent
by e'mail to clochandighter[at]yahoo.co.uk
Graeme Paterson
