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Oceans & Oceania

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BigNose
1214874.  Tue Dec 06, 2016 5:58 pm Reply with quote

I met Anna, Anne and James tonight in Shoreham, I got a book signed and mentioned a fact about Oceans, as prompted by their show!

Q - How deep is the great barrier reef, on average?

A - About 70m ABOVE mean sea level.

What's this about? It's the way sea levels are measured, we always think of the sea being pretty much flat, going up and down a bit with the tides, and that it marks the '0 meter' datum for all heights around the world.

We know the world isn't a sphere, it's an ellipsoid, but its a very complicated ellipsoid and for things like GPS and maps we need an approximation of the shape of the earth before you add all the land bits to it. These approximations are called a Geoids and the most common one (called WGS84) puts the sea level on the east coast of Australia at about 100 metres higher than the sea level on the west coast.

This causes problems. So much so, that GPS doesn't work very well in Australia specifically, and the Australians have their very own sea level measurement that makes more sense for them.


Last edited by BigNose on Wed Dec 07, 2016 7:56 am; edited 1 time in total

 
Alfred E Neuman
1214903.  Wed Dec 07, 2016 2:00 am Reply with quote

BigNose wrote:
This causes problems. So much so, that GPS doesn't work very well in Australia specifically, and the Australians have their very own sea level measurement that makes more sense for them.


You mean something simple like the actual level of the sea? :-)

I don't see why GPS should have a problem if it's a consistent correction that needs to be applied, it should be pretty trivial compared to the calculations required to get your position correct.

And welcome to the forums :-)

 
Strawberry
1214938.  Wed Dec 07, 2016 5:24 am Reply with quote

Yes, welcome.

 
BigNose
1214949.  Wed Dec 07, 2016 5:54 am Reply with quote

Corrections are indeed applied but there are a range of approaches and the 'raw' position obtained from most GPS receivers will be based on the WGS84 reference ellipsoid and may therefore give incorrect sea-level heights at many places around the world, arguably most notable when comparing true sea-level heights on either side of Australia.

http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/geodetic-datums/geoid

http://www.esri.com/news/arcuser/0703/geoid1of3.html

https://en.wikipedia.org/wiki/Sea_level#Difficulties_in_use

 
Alexander Howard
1214950.  Wed Dec 07, 2016 5:57 am Reply with quote

In Australia, it is not just the datum on he GPS that needs adjustment:
all the published latitudes are wrong.

 
BigNose
1214981.  Wed Dec 07, 2016 8:01 am Reply with quote

Yes! See that, the whole continent is drifting north.

Would love to know if this has any legal implications (land boundaries being defined in Lat / Lon co-ordinates rather than any more local reference system).

Can anyone lay legal claim to any 1.5m slices of land or buildings before or after the GPS correction?

 
14-11-2014
1218649.  Fri Dec 30, 2016 1:44 pm Reply with quote

Quote:
the whole continent is drifting north.

Can anyone lay legal claim to any 1.5m slices of land or buildings before or after the GPS correction?

Or claim an intercontinental airfare refund?

Q: Mention an ocean which is a sea.

K: Arctic Ocean. According to the International Hydrographic Organization it's an ocean.

A: Ocean of Storms.

 
Alexander Howard
1218654.  Fri Dec 30, 2016 2:09 pm Reply with quote

BigNose wrote:
Yes! See that, the whole continent is drifting north.

Would love to know if this has any legal implications (land boundaries being defined in Lat / Lon co-ordinates rather than any more local reference system).

Can anyone lay legal claim to any 1.5m slices of land or buildings before or after the GPS correction?


Presumably the boundary between New South Wales and Queensland was defined by reference to latitude ("ůso much of the said colony of New South Wales as lies northward of a line commencing on the seacoast at Point Danger, in latitude 28░8' south...", so could there be homes and businesses near the boundary governed by NSW law that have drifted north to be under Queensland jurisdiction? If you are caught speeding by the boundary, could you raise a "continental drift" defence?

 
Spud McLaren
1218656.  Fri Dec 30, 2016 2:23 pm Reply with quote

Crikey, I had no idea that continental drift was that fast ...

 
Peeeeeteeeee
1226009.  Sun Feb 12, 2017 11:07 pm Reply with quote

Ow....Ow.....Ow......I've got a fact about the oceans. THERE IS NO SUCH THING AS A FISH.

 
dstarfire
1271411.  Sat Jan 20, 2018 2:58 pm Reply with quote

Alexander Howard wrote:
Presumably the boundary between New South Wales and Queensland was defined by reference to latitude ("ůso much of the said colony of New South Wales as lies northward of a line commencing on the seacoast at Point Danger, in latitude 28░8' south...", so could there be homes and businesses near the boundary governed by NSW law that have drifted north to be under Queensland jurisdiction? If you are caught speeding by the boundary, could you raise a "continental drift" defence?


No, because law courts are not that stupid. The initial instrument in defining the boundaries may have used latitude, but everything since then has been declared part of one region or another, and that will not change simply due to continental drift. In other words, when you purchase or rent a piece of property, you're doing so under the authority of one of those regions, thus renewing that regions jurisdiction over the piece of property. Also, the jurisdiction will be an already established feature of that property and won't be changed simply because it conflicts with some old document.

 
chrispr697
1324894.  Fri Jun 21, 2019 9:52 am Reply with quote

Interesting

 

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