JRS: In article , dated Thu, 23
Sep 2004 18:58:46, seen in news:uk.transport.london, James Christie
posted :

With difficulty, because GPS has an accuracy of +/- 100m, unless of
course you are using Differential GPS, but that is mainly a maritime
system.

Differential GPS with respect to a set on the platform (or station)
seems an obvious move - even deals properly with landslides.

But I believe that a platform is the only extended object which comes
that near to just under a train door; if so, use a pair of solid object
detectors below door level, one at each side of the doorway.

Sonar or radar could be used. ISTM likely that if a suitable
electromagnetic structure were fixed to platform edges (e.g. a
perforated metallic strip) then one might use resonant reflection, and
be platform-specific.

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Boltar wrote:

I read apparently that Southern had been having problems with its train doors
not opening on stations north of the Thames because these hadn't been
programmed into the database that uses GPS to know where it is! Is it just me
or is having some GPS controlled database system being used to open the
bloody doors just a teensy bit overkill?? Do they think the driver is
too stupid to know when he's at a station and might try to open them when he's
bowling along at 60?? Sure have some sort of interlock that prevents them
opening when the train is moving but for gods sake , was this implemented just
to keep some technicians in work? And what happens during an emergency?
What next , GPS controlled toilets that won't flush on certain parts of the
network with live networked updates of the turd count at every section?!

No wonder money in the rail industry is in short supply if they're wasting
funds on stupid systems such as this. Someone tell me its not true...

B2003

I don't know why the main line rail companies don't just adopt the
Underground's Correct Side Door Enable system, that prevents doors being
opened on the wrong sides of the train. It can cope with double-sided
platforms, bi-directional platforms, and also automatic cutting in and
cutting out of doors on short platforms. Sorted. Why devise something
over the top to do the same job?

Lee

"Ian Johnston" wrote in message
news:cCUlhtvFIYkV-pn2-KSqR179sj7HU@localhost...

You have to be careful not to confuse the random precison errors with
the unrandom accuray ones. Civilian GPS is designed to be precise to
about +/- 10m, whereas military GPS, which uses different signals, is
precise to +/- 1m. Those errors are random - there is nothing you can
do about them. Selective availability was a deliberate degradation of
accuracy, done by effectively instructing satellites to tell porkies
in their signals, and thereby displace all GPS positions in a
particular area by an ordained amount. That's what doesn't happen
(much) any more, but the precision errors remain.


I have experienced an distinct improvement in accuracy over the last few
years but I am also aware that in certain circumstances GPS is not to be
relied upon. Such events occur, for example, in narrow valleys where the
signals can be "deflected" for want of a better description so GPS wouldn't
work very well in cuttings - or tunnels for that matter.

SA would not be very effiective if all satellites were to displace their
positions by the same amount in the same direction - AFAIK each satellite
had its own displacement which was random - watching a GPS position on a
chart plotter was quite interesting in those days. Now the position doesn't
move and will even plot a position on the correct side of a pontoon.

However when the authorities are playing silly b*ggers with the signal it
tends to be anounced in navigation warnings.....

G

"Tim" wrote in message .. .
On Thu, 23 Sep 2004 15:57:55 +0000, Peter Masson wrote:

(Can GPS identify which line the train is on if adjoining
platforms are different lengths?)

Not with any certainty.

Of course, what happens if the Pentagon decided to turn off GPS for
civilian use without warning (which they've always stated they have the
right to do)?

Or worse, they have a war and introduce deliberate errors into the system
designed to confuse the enemy?

Never mind that , GPS is easily blocked by obstructions such as trees ,
embankments , bridges etc. And as for tunnels... Still , on the bright side
that means LU won't be using it for the doors anytime soon

B2003

(MIG) wrote in message . com...
"Ian Johnston" wrote in message news:cCUlhtvFIYkV-pn2-9bQzpFIyRbud@localhost...
On Thu, 23 Sep 2004 13:05:59 UTC, "Jack Taylor"
wrote:

:
: "Ian Johnston" wrote in message
: news:cCUlhtvFIYkV-pn2-01opgFJcdpZb@localhost...
:
: Or having the stupidity to be blind or partially sighted, eh?
:
: Most visually impaired people are intelligent enough to make enquiries
: before they join trains and join them at the appropriate place to disembark

Well, what's so wrong with arranging things so they don't have to?

Ian

The alternative is to stand at doors that aren't going to open, so how
would it help? Or do you mean rebuilding the stations?

Actually, I think the real issue is do we trust a railway industry
which can't display the correct destination on the train to tell a
visually-impaired person whether it's safe to step out? If not (I
think not) why let over-sophistication cause operating problems?

Today, Barnehurst to Victoria service (375/9) consistently displaying
something line "Mind the gap. We will shortly be arriving at Cannon
Street." Well, the gap between Cannon Street and the entire route of
the journey was pretty big. If any on-train information system
crashes just after the last piece of locational information it
receives, whether from GPS or anything else, is anyone going to bother
about it or warn the passengers?

--- "Annabel Smyth" wrote:

Solar Penguin wrote to uk.transport.london on Fri, 24 Sep 2004:


So how does it keep the count of "The next station is..." displays
updated when that happens?

I don't think it does. My mother was travelling on a train from
Clapham Junction to Arundel; I don't know what had gone wrong,
but ... she told me afterwards that the electronic displays thought
they were going to London, not away from it, so that "The next
station is" was totally out of phase with reality! She said it was
very funny.

Oh... Looks like there are serious problems with the whole thing then. No
wonder the trains can't decide which doors to open if they don't even know
which way they're going! Let's hope they get these bugs sorted soon.

On 24 Sep 2004 14:14:57 -0700, MIG wrote in
, seen in uk.railway:

[snip]
If any on-train information system
crashes just after the last piece of locational information it
receives, whether from GPS or anything else, is anyone going to bother
about it or warn the passengers?

Depends if the staff are even aware! Again talking about 170s, it's
not at all unusual for the drivers display to show correct data whilst
all displays bar those in the front coach show something else
entirely.

--
Ross

From & reply-to addresses will bounce. Reply to the group.

On Fri, 24 Sep 2004 15:56:21 +0100, Annabel Smyth wrote in
, seen in uk.railway:

But there, I suspect, if one loo locks
itself out of service, the others don't, unlike on surface-only trains.

170s don't do this; only the affected toilet will lock itself out. I
suspect it's something that differs according to the unit design.
--
Ross

From & reply-to addresses will bounce. Reply to the group.

"Tim" wrote in message .. .
On Fri, 24 Sep 2004 04:46:28 -0700, David E. Belcher wrote:

SDO

Sorry for being think - what does SDO stand for?


Oops - sorry Tim, should've made it clearer (Selective Door Opening,
for the record).

David E. Belcher

On Fri, 24 Sep 2004 10:37:17 +0100, Matthew Wild
said:

the USAians were
complaining that the main signal would sit right on their military band and
they wouldn't be able to locally degrade Galileo without doing the same to
their own military.

Sounds like a feature, not a bug.

--
David Cantrell | http://www.cantrell.org.uk/david