"Mizter T" wrote in message
...

On 22 Jan, 18:25, MarkVarley - MVP
wrote:
I've often wondered and was reminded today, why is there a delay in
opening the doors for trains arriving at Victoria?
At other terminating stations the doors are released as soon as the
train has stopped, but at Victoria there seems to be a delay, anyone
know why?


You're talking about the arrival of Electrostars into Victoria
mainline station. I don't know the details, but basically they used
GPS to get a fix on where they are. As a safety measure, they also
have a system that means drivers (or can guards also do this?) are
only able to release (i.e. open) the doors on the correct side of the
train. In the western (aka Brighton aka LBSCR [1]) side of the station
the platforms and the approaches to the platforms are all covered up
because of a number of developments that have been built 'on top' of
them - this all messes up the GPS signal reception from the satellite.

Do they really have so little trust in the guards to open the right set of
doors, they have to implement this?

And anyway, it's OK for stations where the platform can always be
determined, but al London, Clapham, E Croydon, Brighton (I could go on), the
actual platform a train is going to arrive at isn't always determinable.
(No, GPS isn't accurate enough to say if its on the up fast/down slow/etc
track.)

It is because one of the platforms at Victoria is shorter than the
others. I think it is platform 7 from memory. It takes the system a
bit longer to open the doors because it has to confirm that it is at
the right platform.

The system also has a problem at smaller two platform stations if one
platform is shorter than the other. There was a case where the london
bound platform could take 12 coaches but the country one only 8. As
the GPS was not sensitive enough to tell which platform the train was
at it would only open 8 coaches in both directions.

On 23 Jan, 09:29, wrote:
It is because one of the platforms at Victoria is shorter than the
others. *I think it is platform 7 from memory. *It takes the system a
bit longer to open the doors because it has to confirm that it is at
the right platform.
by
The system also has a problem at smaller two platform stations if one
platform is shorter than the other. *There was a case where the london
bound platform could take 12 coaches but the country one only 8. *As
the GPS was not sensitive enough to tell which platform the train was
at it would only open 8 coaches in both directions.

Just to clarify a couple of points. On Electrostar the guard does not
release the doors, the driver does it. The Victoria release takes a
while because the train does not receive the GPS signal owing to the
Victoria Place complex. For this reason when we attempt the door
release the train computer asks us where it is in order to know how
many doors to open.

Also note there is no facility to prevent wrong side door releases. t

On Jan 22, 7:07*pm, "Graculus"
wrote:
"Mizter T" wrote in message

...





On 22 Jan, 18:25, MarkVarley - MVP
wrote:
I've often wondered and was reminded today, why is there a delay in
opening the doors for trains arriving at Victoria?
At other terminating stations the doors are released as soon as the
train has stopped, but at Victoria there seems to be a delay, anyone
know why?

You're talking about the arrival of Electrostars into Victoria
mainline station. I don't know the details, but basically they used
GPS to get a fix on where they are. As a safety measure, they also
have a system that means drivers (or can guards also do this?) are
only able to release (i.e. open) the doors on the correct side of the
train. In the western (aka Brighton aka LBSCR [1]) side of the station
the platforms and the approaches to the platforms are all covered up
because of a number of developments that have been built 'on top' of
them - this all messes up the GPS signal reception from the satellite.

Do they really have so little trust in the guards to open the right set of
doors, they have to implement this?

It is a bit daft isn't it? If they don't trust the driver to open the
doors correctly how come they trust him to drive 200 tons of train up
to 100mph?

I suspect its just technology for its own sake, someone came up with a
bullet point list of "cool" features for the train order and some
wally actually signed it off without thinking it through.

B2003

On 23 Jan, 12:10, wrote:
It is a bit daft isn't it? If they don't trust the driver to open the
doors correctly how come they trust him to drive 200 tons of train up
to 100mph?

They don't. AWS exists because they don't trust drivers to spot every
red or yellow signal. TPWS exists because they don't trust drivers to
not ignore AWS, or to approach red signals and junctions at a safe
speed. ATP exists because they don't trust drivers to stay within the
speed limit. Deadman's handles exist because they don't trust drivers
to stay conscious and/or alive. Driver vigilance devices exist because
they don't trust drivers to concentrate on the job, in the
happenstance that they are alive and conscious.

On London Underground, tripcocks exist because they don't trust
drivers to notice red signals. Correct side door enable exists because
they don't trust drivers to open doors on the right side and/or stop
the train roughly next to the platform. Rollback protection exists
because they don't trust drivers to apply the brakes if the train
starts rolling backwards down a hill,

Basically, the only things they do trust the drivers to do is not
override or disable the safety systems. As far as is possible, they
are not otherwise trusted with the safety of the train.

U

On Jan 23, 2:53*pm, Mr Thant
wrote:
Basically, the only things they do trust the drivers to do is not
override or disable the safety systems. As far as is possible, they
are not otherwise trusted with the safety of the train.

The drivers are still driving the train however. All the ATP in the
world won't spot a car thats fallen off a bridge onto the track so the
driver still is required to stay alert. And its down to risk too - if
a train goes across a red light loads of people could be hurt. If the
train isn't quite aligned with the platform and driver opens the doors
someone at the far end of the train thinks "muppet" and walks up to
the next door. Seems to me its a solution looking for a problem.

B2003

"Graculus" wrote in message
...
(No, GPS isn't accurate enough to say if its on the up fast/down slow/etc
track.)
Should be - I get accuracy down to about a metre on a very old hand-held GPS
box. It's certainly good enough to work out the difference at Clapham
Junction because 12-car trains don't get held up when they call on the fast
line platforms, and I've seen it work correctly when a 12-car gets diverted
to the slow platforms. The SDO system just reverts to plan B if it finds
itself somewhere (like the SN platforms at Victoria) where the GPS isn't
good enough.

ISTR reading somewhere that the 377s going to the FCC route are having their
SDO modified to allow for better running between Blackfriars and Kentish
Town.

D A Stocks

"David A Stocks" wrote in message

"Graculus" wrote in message
...
(No, GPS isn't accurate enough to say if its on the up fast/down
slow/etc track.)
Should be - I get accuracy down to about a metre on a very old
hand-held GPS box.

How can you be sure that it's so accurate? I took my Garmin wrist GPS
to Greenwich Observatory, and was crestfallen to discover that my GPS
wasn't nearly as accurate as it claimed. As I recall, it claimed to be
accurate to something like 15', but I had to move about 100' east from
the brass strip before it thought it was at logitude 0 degrees exactly.
I also have doubts about the vertical elevation it reports, though
that's not an issue for trains.

On Fri, 23 Jan 2009, Recliner wrote:

"David A Stocks" wrote in message

"Graculus" wrote in message
...
(No, GPS isn't accurate enough to say if its on the up fast/down
slow/etc track.)
Should be - I get accuracy down to about a metre on a very old
hand-held GPS box.

How can you be sure that it's so accurate? I took my Garmin wrist GPS
to Greenwich Observatory, and was crestfallen to discover that my GPS
wasn't nearly as accurate as it claimed. As I recall, it claimed to be
accurate to something like 15', but I had to move about 100' east from
the brass strip before it thought it was at logitude 0 degrees exactly.

That might be because GPS is giving you a position on the WGS84 ellipsoid,
and the strip at Greenwich is zero longitude on some other datum (Airy
1830?), and the two don't coincide there.

Might be - i don't know the details of the Greenwich strip, or whether
ellipsoids are all defined so as to align at zero longitude, or whether
any difference might be 100 feet.

In any case, if GPS consistently puts the meridian exactly 100 feet east
of the strip, that would be accurate enough for trains, provided that the
coordinates they work with were as measured by GPS, rather than by eg
brass strips and Victorian gentlemen.

I also have doubts about the vertical elevation it reports, though
that's not an issue for trains.

Yes, i believe the altitude is typically much less accurate than the
horizontal position. Something to do with geometry.

tom

--
sh(1) was the first MOO

Tom Anderson wrote:

On Fri, 23 Jan 2009, Recliner wrote:

"David A Stocks" wrote:

(snip)

[...] - I get accuracy down to about a metre on a very old
hand-held GPS box.

How can you be sure that it's so accurate? I took my Garmin wrist GPS
to Greenwich Observatory, and was crestfallen to discover that my GPS
wasn't nearly as accurate as it claimed. As I recall, it claimed to be
accurate to something like 15', but I had to move about 100' east from
the brass strip before it thought it was at logitude 0 degrees exactly.

That might be because GPS is giving you a position on the WGS84 ellipsoid,
and the strip at Greenwich is zero longitude on some other datum (Airy
1830?), and the two don't coincide there.

Might be - i don't know the details of the Greenwich strip, or whether
ellipsoids are all defined so as to align at zero longitude, or whether
any difference might be 100 feet.

In any case, if GPS consistently puts the meridian exactly 100 feet east
of the strip, that would be accurate enough for trains, provided that the
coordinates they work with were as measured by GPS, rather than by eg
brass strips and Victorian gentlemen.


The brass strip dates from the 1970s, so no Victorian gentlemen were
directly involved in that endeavour, and what's more it has since been
replaced by a stainless steel strip.

But basically Tom's analysis is right - Airy's Prime Meridian has been
usurped by those goddamn yanks without so much as an International
Meridian Conference in a typical display of unilateralism and general
lack of gentlemanly behaviour. I speak of course of WGS 84, which
basically was a thorough overhaul of earlier World Geodetic Systems
that were developed by the US Department of Defense and forms the
foundations of the satellite-based Global Positioning System.

You can read more about all this in this entertaining article by Tom
Standage...
http://www.tomstandage.com/FEEDlongitude.html
....in which he notes that the de-facto 'new' prime meridian lies 334
feet to the east of that shown on the ground and runs through a tree
and a rubbish bin in Greenwich Park. He also ponders on an interesting
idea of there being a "meridian boulevard". I would however take issue
with his notion that there can be a "true dividing line between east
and west" - when it comes to longitude, there can be no "true" 0° -
where that meridian lies is always going to be arbitrary.


I also have doubts about the vertical elevation it reports, though
that's not an issue for trains.

Yes, i believe the altitude is typically much less accurate than the
horizontal position. Something to do with geometry.


Past discussions on here that turned to GPS left me in slight
wonderment at the understanding you and others had about it all... and
then you go and ruin it all by casually saying it's "something to do
with geometry"! Splendid ;-)

By the by, I've never owned a GPS device - what fun and games am I
missing out on?