Stone Cairns and Trig Points - What are they?

Wednesday, Apr 25, 2012 at 11:55

Stephen L (Clare) SA

Over the years with our travels around this great country of ours, there has been one type of special landmark feature that gets my attention and for a special reason and these features are known as Trig Points. These permanent structures were erected decades ago, well before the advent of very accurate modern day GPS technology and for the surveyors whose task it was to determine these locations, it often meant months, if not years away from their comfortable homes to venture where no white person had ever been and to permanently mark features on the vast unknown continent of Australia. Many of these early day surveyors would become Explorers in their own right and it is widely accepted that our last true Modern day Explorer and Surveyor was the late Len Beadell who opened up much of the vast unknown Outback, and to lay thousands of kilometres of Outback Highways that all modern day four wheel drivers love to experience and still use many of them to this very day.

Trig Points or Triangulation points have been put there in most cases for a very good reason - to help with geodetic surveys. They were workstations and reference points for surveyors, who would attach their theodolite equipment to the features and fittings within the column, including the three pronged metal plates in the top of the trig point, and from this point the exact coordinates and elevation were recorded and published.

The location of each trig point was selected so that at least two others would be visible from it. When using these trig points, surveyors could work out the angles on the lines of sight between the three points and create a triangular map grid and why the name triangulation or trip point.

Each trig point also contains another plate, usually low down on one side, featuring the bench mark, or as shown on topographical maps, BM of that particular trig point and letters and numbers for the Ordnance Survey Bench Mark. Today their use has now been superseded by aerial photography and satellite mapping, so next time you see these special features, you will know that they were put there for a special reason and you will know your exact location on your topographical map.

Thanks to all that have supplied extra images from around the country, and they can be view here on the forum post that I also listed. Thanks again.

Extra images from the forum post
Smile like a Crocodile
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