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Which electronic charts?


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1 minute ago, ex Elly said:

Administration Bay

Well known for submerged rocks for as long as I can remember well over 30yrs never approach from the south.If wanting to day anchor always go northern side of island.Use to visit friends that looked after ymca camp site.

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3 hours ago, ex Elly said:

That rock in Administration Bay is a newly discovered rock, found about 10 years ago by someone hitting it, and reported to all chart makers by my friend.

It probably still isn't shown on all charts.

 

Interesting. I see it as a cluster of 3 on my iPhone’s Navionics but I’m not sure how it shows on my boat plotter (Navionics card bought new Dec 2020). Will check when we get to L2…

3A8347B9-22ED-4F40-8231-1ECC2E7859B7.png

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28 minutes ago, Fogg said:

Interesting. I see it as a cluster of 3 on my iPhone’s Navionics but I’m not sure how it shows on my boat plotter (Navionics card bought new Dec 2020). Will check when we get to L2…

3A8347B9-22ED-4F40-8231-1ECC2E7859B7.png

Those are user updates, (community edits) they are not part of the LINZ dataset. You'll only see those on your plotter if it supports displaying community edits. 

On your phone you can disable community edits and you'll see the LINZ dataset. 

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Ok thanks. Question: how reliable are community edits? Is there any form of validation before publishing to ensure reliability?

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18 minutes ago, Fogg said:

Ok thanks. Question: how reliable are community edits? Is there any form of validation before publishing to ensure reliability?

It's like Wikipedia. So community policed.

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42 minutes ago, MartinRF said:

Completely off topic but why is it named Administration Bay? There must be a story...

/Martin

one would presume it would named after the millitary camp/headquaters being situated there.But why would you set up a millitary camp facing out to sea towards the enemy when islington bayor home bay would ofer more protection.

Just guess.

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Maybe this has been covered before but what’s the wisdom on community edits? Do savvy sailors have their charts set to hydrographic survey or community edits? Is there any data out there comparing accuracy / reliability?

What is the scope of community edits? How to you make updates? Is it automated or manual? I’ve never looked into it but I understand for example the benefit of combining data from 1000s of boats’ depth sounders readings at different states of tides in popular areas to augment existing surveys. But can anyone just add a totally new rock? What if it’s a scam?

I get the idea of crowd-sourcing for things like Wikipedia where the only risk of bad information is a distorted political statement or flawed scientific findings etc. But navigation & pilotage can be life & death stuff so the standards for validation need to be far higher in my view?

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Back in 2001 when I was first given C-Map at Musket Cove you had to do your own edits. Vavau was about 1/4 mile further West than it should have been from memory (at any zoom), so probably an error in the chart datum?

Going up the Red Sea the Sudan coast jumped about a mile East on some zoom levels, a glitch IT has discussed above.

I guess we were in the first wave of cruisers that set off expecting to carry a pile of paper charts, and then didn't. Nothing quite like plotting the days run on paper however.

DSCF0008.thumb.JPG.24ff39e0810b5a9878939d54d6228fdf.JPG 

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Administration Bay was to be the American naval base in ww2 

They were planning on filling in the  south side of the little island to the main island with the dredgings

This may be like Wiki, may need editing but this is the story I was told, the base was to be on the island so they could keep the sailors out of Auckland at least some of the time

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From Wiki, so it looks like it was the admin base for the gulf defence guns ?

Work began on the Motutapu counter-bombardment battery in 1936.[13] In May 1936 roads to battery had been formed, and the battery and observation post completed by June 1937, guns mounted by end of August 1938, and a temporary camp established at Administration Bay in 1937. War broke out in September 1939 and the military population on the island went from 10 to 200, requiring the construction of additional buildings at Administration Bay and at the observation posts

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20 minutes ago, Jon said:

the base was to be on the island so they could keep the sailors out of Auckland at least some of the time

Overpaid, over sexed and over here. :-) Hard to maintain morale in the trenches where a bunch of yanks are porking your girlfriends back home 

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“Your engines like a drunken sailor”

How do you mean like a drunken sailor ?

“Piston broke”

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1 hour ago, darkside said:

Back in 2001 when I was first given C-Map at Musket Cove you had to do your own edits. Vavau was about 1/4 mile further West than it should have been from memory (at any zoom), so probably an error in the chart datum?

Going up the Red Sea the Sudan coast jumped about a mile East on some zoom levels, a glitch IT has discussed above.

I guess we were in the first wave of cruisers that set off expecting to carry a pile of paper charts, and then didn't. Nothing quite like plotting the days run on paper however.

DSCF0008.thumb.JPG.24ff39e0810b5a9878939d54d6228fdf.JPG 

Brilliant.

I hope they learnt to use a sextant as well.

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https://www.navionics.com/usa/charts/features/community-edits

There's a bit of info here

Personally I find them really annoying and unreliable, little dots all over the place. Find a point of interest and there might be 5 separate dots, some a hundred meters out of position all saying the same thing. Just look at the rock talked about above.

I like the sonar stuff, but that's done by computers so a bit more reliable.

You can click on them to get more info, you can turn them off too.

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7 hours ago, darkside said:

Back in 2001 when I was first given C-Map at Musket Cove you had to do your own edits. Vavau was about 1/4 mile further West than it should have been from memory (at any zoom), so probably an error in the chart datum?

Going up the Red Sea the Sudan coast jumped about a mile East on some zoom levels, a glitch IT has discussed above.

I guess we were in the first wave of cruisers that set off expecting to carry a pile of paper charts, and then didn't. Nothing quite like plotting the days run on paper however.

DSCF0008.thumb.JPG.24ff39e0810b5a9878939d54d6228fdf.JPG 

Yep, I remember that. The whole group was off by the same a mount, a simple offset in the GPS position fixed it. Lots of cruisers asked us why our electronic charts were correct and theirs were not...

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The latest marketing spiel I heard on a new GPS unit was that it use L1 and L5 GNSS signals, as opposed to virtually all the recreational divices out there just uing L1, which putthe accuracy in the +\- 20cm range, with a 25hz update.  

 

Any one able to explain in laymans terms why this additional signal frequecy helps so much, something to do with ionosphere correction? Or is this snake oil?

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43 minutes ago, Ed said:

The latest marketing spiel I heard on a new GPS unit was that it use L1 and L5 GNSS signals, as opposed to virtually all the recreational divices out there just uing L1, which putthe accuracy in the +\- 20cm range, with a 25hz update.  

 

Any one able to explain in laymans terms why this additional signal frequecy helps so much, something to do with ionosphere correction? Or is this snake oil?

As the signal passes through the ionosphere each signal is delayed by a different variable amount depending on the properties of the ionosphere. 

To be able to provide pin point accuracy the receiving system needs to be able calculate the variable delay, this can only be done with 2 signals on 2 different frequencies. 

Having two signals allows the receiving system to determine the offset of each signal do some funky maths and get a highly accurate position. I don't pretend to understand the maths or physics behind this. 

I have not looked at any of the other GNSS constellations or what they provide, but on the GPS constellation (the one run by the USA) the second frequency was always known as L2 and was the encrypted military only frequency. I believe they have since added L2C for commercial use. 

Hence the military are able to decrypt this second frequency, combine it with the recreational frequency and get higher accuracy. 

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