Emergency gps fix

[falconromans]

when using my Satmap or other devices, Should i use true north, mag north or grid north. as when out, at marked Way points the Gps location is not the same as on the posts or gate etc. if the Emergency services need to get to me which should i use in the U.K.
what is the difference and why have we got three Norths, i forgotten my Geography lesson at school.
(Geography for Dummies if possible thanks)

[RaBalder]

Mag north points to the north-pole of the "magnet" Earth. This is a point, but it's location is not at the north-pole.

Magnetic north point is actually moving slowly around.

A compass will have the needle pointing to the magnetic north-pole.


Maps would normally have its north pointing to the north-pole.


"Grid north" I have not a clue about.


If I need to give my coordinates to someone that are going to rescue me, I would try to use some grid-reference that would lead them to me as fast as possible.

Something like...
* North 63 degrees 32 minuttes 18 seconds
* East 18 degrees 18 minuttes 43 seconds

.... I feel pretty sure would be recognized more or less globally.


There could be areas that have some other grid-reference that would be equally known, and then I would have changed to that one if I felt it would lead to faster rescue

....so to summarize: I would always stick with degree-minuttes-second reference listed first....

[JimmyTheHand]

True North - points to Northern end of the Earth's spin Axis (North Pole)

Magnetic North - where the North end of the compass Needle on a points to - which is close to the North Pole, but can vary across the country and changes gradually (something like 1/2 degree every 5 years IIRC)

Grid North - is the direction of the Grid Lines on a Map - this varies across the country as a Map is a flat approximation of the curved Earth surface

You don't need any for emergency services - in UK on land you should try giving them an OS Grid Reference - something like TL 12345 67890 (10 figure) as a GPS will normally give or TL 123 678 as you'd read off a map - if at Sea/in Air then I believe latitude & Longitude to WGS 84 will be most appropriate

If you need to give them something like - headed South from Point X, then I suggest you give magnetic as that is would do from a compass (though in UK the error between them is probably less than most people's ability to hold a bearing) but - best to try giving them details in unambiguous form as possible, e.g. compass bearing 179 degrees
_________________
J.

[ocam]

I quite like the manual's summary:

• Grid North: the direction of a grid line which is parallel to the central meridian on the National Grid.

• True North: the direction of a meridian of longitude which converges on the North Pole.

• Magnetic North: the direction indicated by a magnetic compass. Magnetic North moves slowly with a variable rate and currently is West of Grid North in Great Britain.

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