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The benchmark is just over there - on the other side...

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jimcox
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Tikao Bay, Banks Peninsula

Heights to be done in terms of the Christchurch City Council Datum

Nearest benchmark is on the other side of the harbour - 17km by road drive or 3.6km direct


 
Posted : February 3, 2022 11:05 pm
jhframe
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Piece of cake, if you have a good geoid model.?ÿ (I'm unfamiliar with NZ, so that may be a big if.)


 
Posted : February 3, 2022 11:11 pm
holy-cow
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Take shots on the water level on each side at the same time with different equipment, then set a TBM on each side before checking the OFFICIAL BM with one set of equipment and traversing to the project site with the other.?ÿ Wham bam done.?ÿ Except for the quick communication from side to side to confirm getting the same elevation reading for water level.

How's that??ÿ Off by how much, you say??ÿ Obviously, one set of equipment is faulty.


 
Posted : February 3, 2022 11:19 pm
jimcox
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Posted by: @jim-frame

Piece of cake, if you have a good geoid model.?ÿ (I'm unfamiliar with NZ, so that may be a big if.)

We do have a good geoid model - but no boat

?ÿ


 
Posted : February 4, 2022 12:10 am
jhframe
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Posted by: @jimcox

We do have a good geoid model - but no boat

How long does it take to drive 17km?


 
Posted : February 4, 2022 12:57 am

jimcox
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Posted by: @jim-frame
Posted by: @jimcox

We do have a good geoid model - but no boat

How long does it take to drive 17km?

about 25 mins each way - its a narrow and windy road

?ÿ


 
Posted : February 4, 2022 2:03 am
bill93
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What is tolerance?

Simultaneous GNSS on each side, fairly long session, post-processed together to use only common sats.. Repeat another day, different time of day. Apply geoid.


 
Posted : February 4, 2022 7:40 am
bill93
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Posted by: @holy-cow

Take shots on the water level on each side at the same time

I don't think that will be as good as simultaneous GNSS.

If using water levels, you need stilling wells (buckets with small hole), a calm day, and readings at multiple (simultaneous) times. A lake that size might be okay. A bay will be trickier because of the flow of tides-you might be limited in usable times.


 
Posted : February 4, 2022 7:52 am
holy-cow
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This is a harbor, so there would be differential results over time. But, if readings are taken simultaneously at points of similar distance to the mouth of the harbor (and using stilling wells) the results should be practically identical.?ÿ Running multiple tests would be fun.


 
Posted : February 4, 2022 10:18 am
lurker
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This is perfect use for static gnss observations. Along with the question of who is going to prove you wrong.


 
Posted : February 4, 2022 10:29 am

dmyhill
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If I could set something intervisible on each side of the bay, I would probably just shoot both directions with a total station. Take a GPS measurement on each side as a check, and move on.?ÿ

What are the tolerances? Who will prove you "wrong"? What happens if you are off by x amount?

If this is to just check a box, then my method works. If it is to extend geodetic control, then there would need to be another method.

?ÿ

Let us know how you did it!


 
Posted : February 4, 2022 10:31 am
holy-cow
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Must be near here.

https://www.stuff.co.nz/travel/destinations/nz/89530582/akaroa-harbour-combines-beauty-and-cuteness-with-a-dramatic-past


 
Posted : February 4, 2022 11:50 am
jimcox
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Posted by: @dmyhill

Let us know how you did it!

?ÿ

There are some good suggestions here 🙂

I used RTK.

The biggest problem was where to put the base so I could get radio down into the steep and narrow bay and across the harbour to the marks in Akaroa


 
Posted : February 4, 2022 11:52 am
jimcox
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Posted by: @holy-cow

Must be near here.

https://www.stuff.co.nz/travel/destinations/nz/89530582/akaroa-harbour-combines-beauty-and-cuteness-with-a-dramatic-past

Yup. next bay over from that big building. Just out of shot to the right of the photo

That building was built in WWII to handle the mines they used to protect the harbour

?ÿ


 
Posted : February 4, 2022 11:54 am
jacavell
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Posted by: @jimcox

Tikao Bay, Banks Peninsula

Heights to be done in terms of the Christchurch City Council Datum

Nearest benchmark is on the other side of the harbour - 17km by road drive or 3.6km direct

The foremost authority I know in that part of the world is: W E Featherstone
Western Australian Centre for Geodesy, Curtin University of Technology, Perth, Australia,

[email protected]

I'd bet he can point you in the right direction.


 
Posted : February 5, 2022 6:10 pm

holy-cow
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Where is your project on this view of the area??ÿ When looking at this in GoogleEarth I noted that their are quite a few more named bays other than the ones listed here.


 
Posted : February 6, 2022 6:48 pm
nate-the-surveyor
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I'd want to set a 5 gallon bucket on both sides, with a few holes in it. And, drive a peg, or rebar down to water level. This as a double check. And, to add perspective.

N


 
Posted : February 6, 2022 6:55 pm
jimcox
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Posted by: @holy-cow

Where is your project on this view of the area??ÿ When looking at this in GoogleEarth I noted that their are quite a few more named bays other than the ones listed here.

Since you are playing in Google Earth...

Try to find 41 Tikao Bay Road in street view.

Note the search function puts it too far up the hill


 
Posted : February 7, 2022 1:12 am