/ GPS Epoch

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d_b on 13 Feb 2019

This one wasn't on my radar.  Looks as though GPS kit has it's own answer to the Y2K issue, and some of the older stuff might keel over in April.

https://www.theregister.co.uk/2019/02/12/current_gps_epoch_ends/

I will try to do some digging to find out which gear is accepted, or failing that try to be in a whiteout somewhere remote when it rolls over to see what happens

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DancingOnRock - on 13 Feb 2019
In reply to d_b:

My guess is that companies will issue a statement that their devices are no longer supported when they start to fail. These devices are going to be 15-20 years old?

I have an original ETrex that I think was sold in 1996. The serial number is registered with Garmin will be interested to see if they inform me. 

Actually I better check they have my email address up to date. 

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nniff - on 13 Feb 2019
In reply to d_b:

There are  a few other glitches.  If you try and put the earth onto a nice flat grid, it doesn't really work, so you have a crumple a few bits up to pretend you've got a nice regular system.  One of these points happens to be smack in the Kuwaiti oil fields - a patch of desert presumable dismissed as unimportant when the crumpling was being done.  However, come the early 1990's things were rather different.  I consequently found myself standing next to a few burning oils wells, wondering how my then new and shiny Magellan GPS reckoned that the next point of interest was over 17kms away, when I was certain it was only 3kms.  A close look at the map showed a converging mess of grid lines.  I set off, watching the GPS with interest: as it got to the mess of grid lines, it mentally disembowelled itself, did some big sums, and failed to come up with a sensible answer until we emerged from the mess, at which point it proudly declared that the said point of interest was just over there.

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d_b on 13 Feb 2019
In reply to DancingOnRock:

My guess is that anything sold in the last 10 years will almost certainly be fine.  For 15-20 my gut feeling is that high end branded stuff is more likely to be good than cheap embedded chips but you never really know what is inside a given device.

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d_b on 13 Feb 2019
In reply to nniff:

Good thing nobody was using gps guided weapons around there.  Oh.

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DancingOnRock - on 13 Feb 2019
In reply to d_b:

There weren’t any cheap embedded chips. Everything was designed, produced and licenced by Rockwell. 

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d_b on 13 Feb 2019
In reply to DancingOnRock:

I didn't realise they had a monopoly back then.  Sometimes it feels as though we have always been flooded with dodgy electronics

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DancingOnRock - on 13 Feb 2019
In reply to d_b:

It was military/US government technology. 

It wasn’t until the Gulf war that they turned off the Selective Avaialability. 

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hokkyokusei - on 13 Feb 2019
In reply to d_b:

Did anything bad happen the last time the epoch rolled over?

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DancingOnRock - on 13 Feb 2019
In reply to hokkyokusei:

Nniff seems to have hit the nail on the head. Most GPS was restricted to military use in Kuwait, so a few people got bombed by accident while others got lost in the desert. 

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hokkyokusei - on 13 Feb 2019
In reply to DancingOnRock:

The last epoch rollover was August 21st 1999. There were plenty of people with consumer GPS. I had one myself and was second hand then.

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d_b on 13 Feb 2019
In reply to hokkyokusei:

That's good to hear.  I think I got my GPS around 2000ish. 

IIRC I bought it when I was on a trip and had to put up with lots of people taking the piss and asking if I needed it to find my way to the toilets in the pub...

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MarkJH - on 13 Feb 2019
In reply to nniff:

> There are  a few other glitches.  If you try and put the earth onto a nice flat grid, it doesn't really work, so you have a crumple a few bits up to pretend you've got a nice regular system...

Not sure what you mean by that.  Map projections don't 'crumple' bits up; they are systematic transformations of a spherical surface that produce a plane.  You can apply any grid you want to the resulting plane.  The GPS just estimates it's absolute position in space.  So long as your GPS knows what datum and grid system the map you are using needs, there should be no discrepancy (other than the error in the position estimate).

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nniff - on 13 Feb 2019
In reply to MarkJH:

That may well be the theory, but in practice in some parts of the world it doesn't work particularly well.  My GPS was spot on with where it said I was, but it was buggered when it came to working out the physical distance between two locations each side of the great divide as it appeared to be counting the tiny gaps between grid lines as whole kilometres. The map on the other hand was topographically correct, but the grid lines were garbage.

I've also been in a similar position in Indonesia.  I established fairly quickly that the thing (an etrex this time, set to the correct datum and grid system) was lying through its teeth and gave up on it. I subsequently tested it on a small island on which my position was not in doubt.  I was apparently making good progress about 1km offshore.  My idea why that was.

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Niall_H - on 14 Feb 2019
In reply to DancingOnRock:

> It wasn’t until the Gulf war that they turned off the Selective Avaialability. 

You sure?  This article ( https://www.gislounge.com/us-discontinues-selective-availability-of-gps-to-public/ ) suggests it happened in 2000.

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DancingOnRock - on 14 Feb 2019
In reply to Niall_H:

Ok. Yes. They only turned it off for the duration of the Gulf War.

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