Trig points - a general discussion

[Kerry]

The following ICSM wording is a reasonable explanation. The key word being "trigonometry"

Hilltop survey marks are often referred to as 'Trig Points' or 'Trig Stations' because trigonometry is used to calculate their positions – their full title is Trigonometric Point or Station. They are permanently marked on the ground and usually have a beacon or cairn of rocks directly above them so they can be seen from a distance. Sometimes the Trig Station is an observation pillar on which the surveying instrument is placed – including theodolites, Electronic Distance Measuring devices (EDMs) and GPS antennas.

The actual in ground survey mark used (apart from say pillars) can be typically similar depending on what authority installed them. It is more the purpose of the mark that generally defines what one might class it.

The typical quad or triangle supported beacon or pillar make setting instrucments on these marks reasonably easy but site access in many cases controlled what type of beacon was constructed. The rock cairn typically uses local materials that don't need to be lugged into a site. So next time you see a rock cairn think that generally there is a permanent mark at the bottom of the beacon post etc and to set an instrument over this mark requires the cairn to be disassembled rock by rock then reassembled when the survey is complete. Also in this case there will generally be an eccentric mark associated with the main trig station

[pjmpjm]

The rock cairn typically uses local materials that don't need to be lugged into a site. So next time you see a rock cairn think that generally there is a permanent mark at the bottom of the beacon post, etc., and to set an instrument over this mark requires the cairn to be disassembled rock by rock then reassembled when the survey is complete.

Thanks for the very interesting information!

And I never knew that a PM would be located under the stone cairn . . .

Not that I'm now tempted to find it -- stone by stone . . .

[ST_7]

The rock cairn typically uses local materials that don't need to be lugged into a site. So next time you see a rock cairn think that generally there is a permanent mark at the bottom of the beacon post, etc., and to set an instrument over this mark requires the cairn to be disassembled rock by rock then reassembled when the survey is complete.

Thanks for the very interesting information!

And I never knew that a PM would be located under the stone cairn . . .

Not that I'm now tempted to find it -- stone by stone . . .

This is what an unpiled Trig looks like - http://geocaching.com.au/gallery/image/28399

In all the surveyors sketches that I have come across, it is generally refered to as the 'trig plug'.

[pjmpjm]

This is what an unpiled Trig looks like - http://geocaching.com.au/gallery/image/28399 In all the surveyors sketches that I have come across it generally refered to as the 'trig plug'.

Many thanks! This is very interesting, to say the least. I really had no idea. The photo is a real eye-opener.

Now I may in fact be tempted when I next encounter a rock cairn . . .

[Teirae]

now we are going to be debating rock cairns...i know of one...and i know its not a servey point or trig point or anything...its the remains of an old church they used and piled it up. i guess it marks the spot where a church once stood...

[Kerry]

This is what an unpiled Trig looks like - http://geocaching.com.au/gallery/image/28399 In all the surveyors sketches that I have come across it generally refered to as the 'trig plug'.

Many thanks! This is very interesting, to say the least. I really had no idea. The photo is a real eye-opener.

Now I may in fact be tempted when I next encounter a rock cairn . . .

Yes they are quite easy to pull apart but I doubt you have the means or instruments to put it back togeather with any degree of accuracy? Also it is basically illegal to disturb a survey mark unless you are authorized to do so.

[Zalgariath]

I have decided I wont be listing the UK Trig Points I find here as there is already a DEDICATED site that ONLY has Trigs http://www.trigpointinguk.com/. 8000ish on their database and Im not a fan of ever dual listing a feature so hopefully they use GPX format and I can d/l all of them

[caughtatwork]

I have decided I wont be listing the UK Trig Points I find here as there is already a DEDICATED site that ONLY has Trigs http://www.trigpointinguk.com/. 8000ish on their database and Im not a fan of ever dual listing a feature so hopefully they use GPX format and I can d/l all of them

Sweeeeet!

[Zalgariath]

THEY DO USE GPX

BUT! They use the same number system as GCA (TPXXXX) so I might have to create a separate database on GSAK for them as otherwise I will get clashes with GCA Trigs

[pjmpjm]

and I can d/l all of them

I first thought you wrote that you would log all of them . . .

[Yurt]

So where does this set fit in? It's just like a trig but it says on the description that it's a permanent marker, or the series is.
http://geocaching.com.au/cache/tp5620 - there's three more there apparently.

We found one like this a few weeks ago about halfway between two logged trigs. They were only about 400 metres apart and this one was exactly like a trig but with a cap not vanes and the plaque had a PM number so it's some sort of permanent marker. Didn't log it but have the photos.

[rogerw3]

yes that is very interesting, but I think that despite the similar appearance, these where set up to check the alignment of the fuel pipe line, the check points would have to be elevated for ease of visibility. As a secondary function they may be used by the University as a survey teaching aid. They are clearly marked as a PM (Permanent marker) not as a TS (Trigonometric Station).

After some searching I came across this pdf well I printed and scanned it since I don't know how to insert a pdf here!

Again it shows these as PM, if they were Trigs they would have a TS number.

[pjmpjm]

Yes that is very interesting, but I think that despite the similar appearance, these where set up to check the alignment of the fuel pipe line, the check points would have to be elevated for ease of visibility. As a secondary function they may be used by the University as a survey teaching aid. They are clearly marked as a PM (Permanent marker) not as a TS (Trigonometric Station). After some searching I came across this pdf well I printed and scanned it since I don't know how to insert a pdf here!
Again it shows these as PM, if they were Trigs they would have a TS number.

Very interesting indeed. Many thanks for sharing.

[ST_7]

So where does this set fit in? It's just like a trig but it says on the description that it's a permanent marker, or the series is.
http://geocaching.com.au/cache/tp5620 - there's three more there apparently.

These Permanent Marks are part of the Newcastle EDM Testline. Surveyors use these testlines to calibrate their instruments. They are not trig stations.

The following quote is from the 'Surveyor General’s Directions - No. 5 - Verification of Distance Measuring Equipment'

The Surveying and Spatial Information Regulation 2006 requires surveyors to verify their Electronic Distance Measuring (EDM) equipment in relation to the State Primary Standard of measurement, in the form of pillared testlines. The Surveyor General has established eighteen concrete pillared EDM Testlines throughout NSW, three in Sydney and the remainder located in regional centres throughout the State. Each pillar contains a stainless steel base plate with a 5/8" Whitworth screwed spigot to receive the tribrach. The spigot is protected by an acorn nut and PVC cap. Use of all testlines is provided free of charge to the owners of EDM equipment for the calibration of their instruments.

http://geocaching.com.au/gallery/image/28842

[pjmpjm]

These Permanent Marks are part of the Newcastle EDM Testline. Surveyors use these testlines to calibrate their instruments. They are not trig stations.

Very helpful. Thanks, Delta-squad.