Degree confluence project

Colin Blackburn said:

Some of you may know about this project:

confluence.orgconfluence.orgOpen ↗

which aims to find a use for GPS! Points on the earth
where the degree lines of longitude and latitude meet are
visited, photographed and then documented on the above
website.

What people may not know is that the guy who started the
whole thing off, Alex Jarrett, runs a business delivering
stuff by bicycle:

confluence.orgalexOpen ↗
pedalpeople.compedalpeople.comOpen ↗

Colin

I hope he has more luck than a local parish council. We live
near the Greenwich Meridian and for the Millenium the next
village decided to install a marker. I can only presume that
some local decided to GPS it rather than look at the map
because the Ordinance Survey 25,000 shows the Meridian going
unambiguosly diagonally across a cross roads junction, the
marker post is some 100yds up one of the roads.

Tony

Tony Raven said:

Colin Blackburn said:

Some of you may know about this project:

confluence.orgconfluence.orgOpen ↗

which aims to find a use for GPS! Points on the earth
where the degree lines of longitude and latitude meet are
visited, photographed and then documented on the above
website.

What people may not know is that the guy who started the
whole thing off, Alex Jarrett, runs a business delivering
stuff by bicycle:

confluence.orgalexOpen ↗
pedalpeople.compedalpeople.comOpen ↗

Colin

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium the
next village decided to install a marker. I can only
presume that some local decided to GPS it rather than look
at the map because the Ordinance Survey 25,000 shows the
Meridian going unambiguosly diagonally across a cross
roads junction, the marker post is some 100yds up one of
the roads.

GPS gives you lovely figures to three decimal places or
whatever. Shame it's all deliberately inaccurate for anyone
other than NATO 😉.

Jon Senior said:

"Doki" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

GPS gives you lovely figures to three decimal places or
whatever. Shame

it's

Quoted message said:

all deliberately inaccurate for anyone other than
NATO 😉.

During the first Gulf war, any GPS unit apparently gained
the accuracy of the full system because the Americans
couldn't afford to distinguish between the two. So all you
need to do is wait until the Yanks invade another
country... shouldn't take very long ;-)

T'other way round. It used to be that civilian had errors
built in and military was more accurate (Selective
Availability). In war zones the civilian accuracy would be
further degraded to make it less useful to the other side.
On May 1 2000, President Clinton announced they were ceasing
selective availability so that civilian became virtually as
good as military, give or take a few tens of thousands spent
on the electronics. Instead of global degradation they now
use regional degredation of GPS when they don't want the
other side using it.

clinton4.nara.gov0053 4.htmlOpen ↗

Tony

"Jon Senior" <jon@restless_REMOVE_lemon.co.uk> wrote in message
"]news:[email hidden]...

Quoted message said:

"Doki" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

GPS gives you lovely figures to three decimal places or
whatever. Shame

it's

Quoted message said:

all deliberately inaccurate for anyone other than
NATO 😉.

During the first Gulf war, any GPS unit apparently gained
the accuracy of the full system because the Americans
couldn't afford to distinguish

between

Quoted message said:

the two.

They didn't have enough military GPS units, so used civilian
ones and turned off SA to make them work.

Quoted message said:

So all you need to do is wait until the Yanks invade
another country... shouldn't take very long ;-)

The inaccuracy to which you both refer, Selective
Availablity, got turned off temporarily during gulf I, then
again in May 2000. Ie you've had full accuracy for nearly
four years now.

ngs.noaa.govsans SAOpen ↗

cheers, clive

Tony Raven said:

Colin Blackburn said:

Some of you may know about this project:

confluence.orgconfluence.orgOpen ↗

which aims to find a use for GPS! Points on the earth
where the degree lines of longitude and latitude meet are
visited, photographed and then documented on the above
website.

What people may not know is that the guy who started the
whole thing off, Alex Jarrett, runs a business delivering
stuff by bicycle:

confluence.orgalexOpen ↗
pedalpeople.compedalpeople.comOpen ↗

Colin

Quoted message said:

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium the
next village decided to install a marker. I can only
presume that some local decided to GPS it rather than look
at the map because the Ordinance Survey 25,000 shows the
Meridian going unambiguosly diagonally across a cross
roads junction, the marker post is some 100yds up one of
the roads.

The question is whether they intended to mark the historical
Greenwich Meridian (actually there are two), or the nearest
approx to the current world mapping zero longitude line.
There's roughly 100 yards difference.

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
["]http://www.dai.ed.ac.uk/homes/cam/]

Doki said:

Tony Raven said:

Colin Blackburn said:

Some of you may know about this project:

confluence.orgconfluence.orgOpen ↗

which aims to find a use for GPS! Points on the earth
where the degree lines of longitude and latitude meet
are visited, photographed and then documented on the
above website.

What people may not know is that the guy who started the
whole thing off, Alex Jarrett, runs a business
delivering stuff by bicycle:

confluence.orgalexOpen ↗
pedalpeople.compedalpeople.comOpen ↗

Colin

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium
the next village decided to install a marker. I can only
presume that some local decided to GPS it rather than
look at the map because the Ordinance Survey 25,000 shows
the Meridian going unambiguosly diagonally across a cross
roads junction, the marker post is some 100yds up one of
the roads.

Quoted message said:

GPS gives you lovely figures to three decimal places or
whatever. Shame it's all deliberately inaccurate for anyone
other than NATO 😉.

The deliberate errors in civilian GPS signals were turned
off in May 2000, and will never be restored (because they
have better ways of confusing the enemy now).

Most current consumer hand-held GPS units today will give
readings in good conditions repeatable within 5-10 metres,
and will detect movement of less than a metre.

The military use an extra signal set which reduces errors a
bit more, and in war scenarios the system can be tuned a bit
to be more accurate at a particular place.

Using survey grade GPS equipment with a local base station
it's possible to improve on this by at least an order of
magnitude.

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
["]http://www.dai.ed.ac.uk/homes/cam/]

Tony Raven said:

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium the
next village decided to install a marker. I can only
presume that some local decided to GPS it rather than look
at the map because the Ordinance Survey 25,000 shows the
Meridian going unambiguosly diagonally across a cross
roads junction, the marker post is some 100yds up one of
the roads.

Is it the Prime Meridian or the Greenwich Meridian? There's
a difference of about 100 yards between the two.

Mine, using WAAS when its available, which I think is a bit intermittent, gives accuracy of better than a metre.

Following the track log of one of my rides overlaid onto an accurate chart on the chartplotter you can see where I pulled out to overtake someone and where I cut one of the corners. The start and finish points of the tracklog touch.

That is all with good clear reception and WAAS definately on.

as others have noted Selective availability has been off for some time, although the aviation authorities warn against relying on GPS around military installations especially during exercises because they can use battlefield interference to "move" themselves somewhere else!

Steve D

Gonzalez said:

On Mon, 29 Mar 2004 13:37:50 +0100, "Tony Raven" <junk@raven-

family.com said:

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium
the next village decided to install a marker. I can only
presume that some local decided to GPS it rather than
look at the map because the Ordinance Survey 25,000 shows
the Meridian going unambiguosly diagonally across a cross
roads junction, the marker post is some 100yds up one of
the roads.

Is it the Prime Meridian or the Greenwich Meridian?
There's a difference of about 100 yards between the two.

Can you explain the difference because I can't find anything
via Google that indicates anything other than the Prime
Meridian is the Greenwich Meridian nmm.ac.uksitOpen ↗
e/request/setTemplate:singlecontent/contentTypeA/conWebDoc/-
contentId/1343/navId/00500300f00e.

I did find the following on the Royal Greenwich Observatory
web site that explains why a GPS is 100m off at zero
longditude though - nmm.ac.uksetTeOpen ↗
mplate:singlecontent/contentTypeA/conWebDoc/contentId/416/n-
avId/00500300f00e

Tony

sdorrity said:

Mine, using WAAS when its available, which I think is a bit
intermittent, gives accuracy of better than a metre.

WAAS-type correction signals are still experimental over
Europe, and at the moment mostly make errors worst rather
than better. Your GPSR may not know this :-)

Quoted message said:

Following the track log of one of my rides overlaid onto an
accurate chart on the chartplotter you can see where I
pulled out to overtake someone and where I cut one of the
corners. The start and finish points of the tracklog touch.

I presume they touch to the nearest pixel on your computer
display. So how many metres does a pixel of your computer
display cover on that mapping scale?
--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
["]http://www.dai.ed.ac.uk/homes/cam/]

Tony Raven said:

Gonzalez said:

On Mon, 29 Mar 2004 13:37:50 +0100, "Tony Raven" <junk@raven-

family.com said:

I hope he has more luck than a local parish council. We
live near the Greenwich Meridian and for the Millenium
the next village decided to install a marker. I can only
presume that some local decided to GPS it rather than
look at the map because the Ordinance Survey 25,000
shows the Meridian going unambiguosly diagonally across
a cross roads junction, the marker post is some 100yds
up one of the roads.

Is it the Prime Meridian or the Greenwich Meridian?
There's a difference of about 100 yards between the two.

Can you explain the difference because I can't find
anything

This explanation is from memory, in a local magazine called
"The Blackheath Guide".

Prime Meridian is defined as the line passing through the
North and South Poles and the eyepiece cross-hairs on the
transit circle telescope in the Royal Greenwich Observatory.

Greenwich Mean Time was defined from the Prime
Meridian. Midday was the mean time when the Sun crossed
the Prime Meridian.

The Greenwich Meridian is defined by time. It is the line
which the Sun crosses at midday

Since 1977 time has been defined by Atomic clocks. Now, at
midday, the mean sun crosses a line about 100 yards to the
west of Greenwich.

On Tue, 30 Mar 2004 20:02:17 +0100, Gonzalez
<[email hidden]> wrote:

I cycled by the Millennium Dome last night. It has no fewer
than four meridian lines marked by metal strips across the
cycleway and footpath.

The Easterly line is most prominent, with the strip
continuing out about 2m over the Thames on a sort of
horizontal post. The second (about 10m West) has the Zero
Degree Laser directly above it. The third and forth are
about 100m East and are less prominent.

My 1:25000 map of Greenwich has one "Greenwich Meridian"
marked in a fairly thick (0.6mm approx) green line. The
thickness of the line makes it hard to determine precisely
which line it represents (0.4mm = 10m), but it seems to be
one of the eastern lines, which is odd as it certainly
passes through Flamsteed House, and probably the Old
Greenwich Observatory, but not the Royal Greenwich
Observatory and the famous brass line near the original
magnetic clock.

I have found the following web site which, in part, agrees
with my assertions.

hardwick-cambs.org.ukmeridian.htmOpen ↗

===============WEBSITE QUOTE==============

Hardwick, the Millennium and the Meridian

As the millennium approaches, there is increasing interest
in the prime meridian, the line of longitude passing through
Greenwich (the site of the old Royal Observatory and the
"Millennium Dome"😉 which is used as a reference for all
other longitudes on Earth and for the international standard
of time: Greenwich Mean Time. The old millennium will give
way to the new at midnight GMT on 31 December 1999 (or 2000,
but let's not get into that argument here), when it will be
locally midnight everywhere on the Greenwich meridian,
which, as many readers will know, passes close to Hardwick.
The course of the line may be ascertained from the local
Ordnance Survey map. A sundial commemorating the Queen's
Silver Jubilee marks its crossing of the Toft to Comberton
road. A little way north it enters Hardwick parish, crossing
Toft Road a little to the north of Halfway House. After
crossing the Wimpole Way, it passes about a quarter of a
mile to the west of Hardwick village centre, reaching St
Neots Road a few yards west of the Enterprise Café. What is
less well known is that there are in fact several Greenwich
meridians all slightly displaced from one another. The
official one, aligned with the Transit Circle of Airy
(Astronomer Royal, 1835-81) and marked by a brass line set
in the courtyard of the Old Royal Observatory, is actually
18ft east of the one used by the Ordnance Survey, whilst the
reference meridian for the widely used global positioning
system (GPS), which will almost certainly become the new
international standard before too long, lies a further 336ft
to the east. This puts it just to the east of the Enterprise
Café. Either this site or the Toft Road crossing would be
possible locations for any monument which the village may
wish to erect to mark the millennium. Incidentally, in spite
of the Millennium Clock at Greenwich counting down the
remaining seconds of this millennium, we do not know for
sure exactly how much time is left. This is because it is
sometimes necessary to insert a leap second at the end of
June or December to allow for the slightly varying rotation
of the Earth, and this can be predicted only a few months in
advance. One last thought: if a leap second turns out to be
necessary at the end of December 1999, there will be a whole
second's delay between the end of the old millennium and the
start of the new.

Andy Smith, 10 September 1997.