What's the difference between a trig point and a survey mark

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Goldenwattle
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What's the difference between a trig point and a survey mark

Post by Goldenwattle » 01 October 15 6:46 pm

Surely they both involve surveying. They both have metal plaques on the ground and posts.

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caughtatwork
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Re: What's the difference between a trig point and a survey mark

Post by caughtatwork » 01 October 15 7:39 pm

TrigPoints were used to survey Australia back in the 1970's. There were limited numbers. They were generally a marker with a deice on top so you could see them from a long distance.
https://en.wikipedia.org/wiki/Triangula ... #Australia

Survey markers are used everyday to map areas.

Not much difference except that a TP is not a SM and we don't list SM's separately.

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ziggiau
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Re: What's the difference between a trig point and a survey mark

Post by ziggiau » 01 October 15 9:52 pm

Having recently become accustomed to looking downwards to find survey markers everywhere (or consulting SIX Maps to go find them specifically), when logging them and reviewing their placement on the map, it's taking quite some time to load due to the numbers logged. Would their be any rationale in splitting survey marker locationless caches up into regions to be able to handle the volume or is that just asking for trouble?

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spatialriq
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Re: What's the difference between a trig point and a survey mark

Post by spatialriq » 01 October 15 10:15 pm

At C@W says, Trig points are kind of from a previous era. With the advent of GPS and modern theodolites (total stations) it's all SSM's (Standard Survey Marks) now as line-of-sight isn't as important as it used to be. With differential GPS (2 GPS receivers, 1 set up on a known point, and 1 where-ever you like) you can accurately map to centimetre level these days.

Trust me, I'm a Surveyor! :lol:

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Chwiliwr
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Re: What's the difference between a trig point and a survey mark

Post by Chwiliwr » 02 October 15 1:12 pm

Goldenwattle wrote:Surely they both involve surveying. They both have metal plaques on the ground and posts.
In WA most trig points are disguised as State Survey Marks so apart from where an actual trig mast is present and because they appear to be recorded with the same ID in the government database I have been identifying them from the trig markings on the older topographical maps that I got access to.

Around the Perth metropolitan area most of the old trig points have disappeared or are now on private property. I have also been finding that a significant number of country trig points are in the middle of farms so not accessible.

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ziggiau
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Re: What's the difference between a trig point and a survey mark

Post by ziggiau » 14 October 15 5:14 pm

spatialriq wrote:At C@W says, Trig points are kind of from a previous era. With the advent of GPS and modern theodolites (total stations) it's all SSM's (Standard Survey Marks) now as line-of-sight isn't as important as it used to be. With differential GPS (2 GPS receivers, 1 set up on a known point, and 1 where-ever you like) you can accurately map to centimetre level these days.

Trust me, I'm a Surveyor! :lol:
So does that mean there will never been any new trig points placed?

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caughtatwork
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Re: What's the difference between a trig point and a survey mark

Post by caughtatwork » 14 October 15 7:16 pm

If you find a TrigPoint which has a marker which says TRIGONOMETRICAL STATION then, sure. If you find a SSM, then nope. There are thousands of unlisted TP's in NZ :-)

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Tyreless
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Re: What's the difference between a trig point and a survey mark

Post by Tyreless » 15 October 15 8:36 am

I had trouble working out what constituted a trig station when I was in NZ earlier this year. Unlike the hierarchy in Australia they describe their survey marks in terms of what "order" they fall into (see http://www.linz.govt.nz/data/geodetic-s ... ate-orders).

Does anyone know what counts as a trig in NZ?

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caughtatwork
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Re: What's the difference between a trig point and a survey mark

Post by caughtatwork » 15 October 15 8:47 am

If it's got a plaque that says Geodetic Survey Mark and it's got a beacon, I'd say it's a TrigPoint.

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Richary
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Re: What's the difference between a trig point and a survey mark

Post by Richary » 15 October 15 7:39 pm

I added one in Dunedin (at whatever the top of the mountain is where the TV transmitters are) when I was over for the mega. I also spotted another one by the side of the highway heading back to ChCh but didn't have a chance to pull over. That one was strange as it was in the middle of a big flat stretch and not on a hill (though the countryside was flat all around so it would have been visible for miles) but looked like a traditional Aussie trig with vanes etc.

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Re: What's the difference between a trig point and a survey mark

Post by Dik: » 15 October 15 11:49 pm

Tyreless wrote:I had trouble working out what constituted a trig station when I was in NZ earlier this year. Unlike the hierarchy in Australia they describe their survey marks in terms of what "order" they fall into (see http://www.linz.govt.nz/data/geodetic-s ... ate-orders).

Does anyone know what counts as a trig in NZ?
Well I always understood Australian trig points to be 1st order points. I.e. a 2nd order point is referenced to a 1st order etc. But it would appear in NZ they are called 0 order.
A trig point is a point that has been defined to the highest order and other survey marks must be referenced by triangulation to 3 trigs. Lesser points may be created by referencing 3 points of higher order, but a reference back to the trig network is always possible.
Think of a trig point as a GPS satellite on the ground.
Think of lower order points like a multi geocache that is an offset from a GPS point but located where the GPSr can't see the sky, eg indoors, down a mine shaft, tunnel etc.

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Browngang
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Re: What's the difference between a trig point and a survey mark

Post by Browngang » 22 October 15 1:41 pm

For those of you guys interested in trig points and SSM's etc. I found this cache while in the US of A recently. In a very cool town, St Augustine, America's first European settlement in Florida.
http://www.geocaching.com/geocache/GC1M ... c1535edbc8#

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