Join us in the Summit Inn to celebrate the return of the YOSM in it's new format.
The YOSM was originally a 2002 moving virtual cache that periodically moved to new trigpoints around the country allowing people to log multiple finds on the same cache by visiting different trigpoints that had held the YOSM virtual coordinates previously. In 2017 Groundspeak made changes to the guidelines which meant that unfortunately the YOSM was archived.
The YOSM series now returns in a new format, with a properly organised national series using traditional geocaches. Existing YOSM numbers are retained and new numbers will be given to trigpoints that didn't formally hold a YOSM. Existing trigpoint caches may be numbered into the series and soon trigpoints across the county will once again be on the geocaching map.
The Summit has been chosen as an appropriate place to celebrate trigpoints, which are often (not always!) found at the highest points. Join us for a short chat and celebration of these concrete icons on the day the new YOSM series launches nationally across the UK. As always, there is no need to purchase anything in order to attend the event.
The intention is for a short series of geocaches to be published around 7:30pm that might just lead us to a nearby trigpoint. A slightly earlier publication time is planned so we can get there before sunset (which is around 8:15pm).
The trig pillar was first used in the retriangulation of Great Britain on 18 April 1936. On that day, a group of surveyors gathered around a white concrete pillar in a field in Cold Ashby and began the retriangulation of Great Britain. Triangulation is a mathematical process that makes accurate map making possible.
In 1935 Ordnance Survey, in a project led by Brigadier Martin Hotine, decided to implement a complete new control network for the whole country and at the same time unify the mapping from local county projections onto a single national datum, projection and reference system. This lead to the OSGB36 datum and The National Grid, both of which are still with us today.
The man responsible for the trig pillar that we all recognise today was Brigadier Martin Hotine. Born in 1898 in Wandsworth, London, Hotine became head of the Trigonometrical and Levelling Division at OS. The Brigadier was responsible for the design, planning and implementation of the retriangulation and he designed the iconic trig pillar. He designed them to provide a solid base for the theodolites used by the survey teams to improve the accuracy of the readings obtained. As a result, they are sometimes referred to as ‘Hotine Pillars’.
There were 6,500 + trig pillars erected across the country. In practice, a theodolite would have been secured to the top mounting plate and made level. It would then be directly over the brass bolt underneath the pillar. Angles were then measured from the pillar to other surrounding points. For the highest accuracy primary points in the retriangulation, many rounds of angles would have been measured with the observations taking several hours. But time and technologies have moved on enormously to the point where the traditional trig pillar is now obsolete in its original guise.
Many are lost today, farming, housing, coastal erosion, even vandalism are all reasons for them disappearing but we celebrate those that remain with with the YOSM series.