magnetic offset and the shift of the planet?

[Arghiro]

25cm, or less than a foot? I doubt that GPS is that accurate, even with Differential algorithms applied. I can't see something that small affecting anything the you & I could measure.

And, yes, what has happened (and still happening) in Japan is horrendous. Probably one of the best prepared countries (and richest) in the world for such disasters, and utterly powerless to stop it. But I reckon the death toll & devastation would have been far far higher if Japan hadn't worked so hard to build earthquake resistant structures.

[DaveS]

Elsewhere, or maybe later in the same report, it was mentioned that the main Japanese island had moved 2.4 metres. I would have thought that quite sufficient to upset road use sat navs unless they use DGPS. Anyone know?

[Arghiro]

Elsewhere, or maybe later in the same report, it was mentioned that the main Japanese island had moved 2.4 metres. I would have thought that quite sufficient to upset road use sat navs unless they use DGPS. Anyone know?

Again I doubt it. I don't think that maps are that accurate. Remember that a road marked on a map is much larger than reality. If you scaled up the average road marked on a map I suspect it would be about 100mtr wide. At max magnification, my google earth GPS often shows me driving thro fields alongside the road anyway.

[Telo]

my google earth GPS often shows me driving thro fields alongside the road anyway

So now we know why you were pushing the car when you did your leg in.

[Arghiro]

my google earth GPS often shows me driving thro fields alongside the road anyway

So now we know why you were pushing the car when you did your leg in.

Actually, I had stopped across a driveway to sort summat out & the owner of the house came back - but the car wouldn't restart. So I tried to push it out of the way . . .

I am not as fit & young as I used to be. or I thought I was!

[DaveS]

Elsewhere, or maybe later in the same report, it was mentioned that the main Japanese island had moved 2.4 metres. I would have thought that quite sufficient to upset road use sat navs unless they use DGPS. Anyone know?

Again I doubt it. I don't think that maps are that accurate. Remember that a road marked on a map is much larger than reality. If you scaled up the average road marked on a map I suspect it would be about 100mtr wide. At max magnification, my google earth GPS often shows me driving thro fields alongside the road anyway.

I think it depends on both the hardware and the mapping software. I've just bought one of Maplin's GPS dongles and tried it for the first time last night. It comes with a trial application that shows position on a Google Earth map. With 4 satellites acquired (this inside a stone built house) it consistently showed a position within 2 metres horizontally and 4 metres vertically of reality.

Back to car sat navs: their road data is held in vector format so shouldn't be subject to scaling effects. I know that mine (a Navman) realises I've left a motorway when I'm about half way down the slip road, maybe 3 metres to the side of the main carriageway. This is what made me wonder about the effect of the Japanese 2.4m shift.