45° South ?? (Central Otago) Traditional Cache
45° South ?? (Central Otago)
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Difficulty:
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Terrain:
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Size: 
(small)
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This cache is situated on the 45th parallel so you are half way to the equator from the South Pole.
As you will see from your GPS the co-ordinates do not match with the co-ordinates on the monument. The reason for this is the GPS mapping system is different to the old cartography type of mapping system. The variation is enough that boats can run aground if using a GSP and looking at an old map.
We have calculated that the two readings are about 180 metres apart. Would be interested to know if anyone else can confirm our calculations. Based it on my sons knowledge of maths and degrees etc.
Note posted by alsjfs
"The plinth would have been established using NZ Geodetic Datum 1949 (A geodetic datum is a mathematical model of the Earth's shape called an ellipsoid, which looks like a sphere that has been squashed from the top and bottom). The current datum is NZGD 2000, which is the same as the WGS84 geocachers use (to the accuracy that we can obtain). The Land Information NZ website has a converter available, and NZGD 2000 S44 59.902 converts to NZGD 1949 S45 00.000, so Guzzi Riders' value is spot on. The 180 metre difference is near enough, we calculate it as 181.6m.
A datum change is of no concern to land owners, their boundaries are still in the same place, only the way of describing them has changed."
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