lowest trig point?
John Brewer
of 2m on the Scottish mainland - place called Rhunahaorine Point, just
opposite Ghigha (OS Landranger 62) and/or
http://www.multimap.com/map/browse.cgi?X=169000&Y=650000&scale=25000
The obvious questions are a) is there a lower one in the UK and, b) is
the height given the height of the brass plate or does it refer to
something else?
...oh, and c) has this topic cropped up previously? If so, my
apologies....;-)
John B
RJ Webb
Have a browse around the Angry Corrie website.......
http://bubl.ac.uk/org/tacit/tac/tac53/frompill.htm
2m is the lowest in Scotland, there is another 2m one near Beauly.
http://www.streetmap.co.uk/streetmap.dll?G2M?X=255670&Y=847730&A=Y&Z=3
A group visited your example at one of th Marilyn bagging conventions
- I settled for a trip to Scarba.
I once visited a 6m one on Lady Isle, just off Troon.
The lowest in Britain is in the Fens.. at -1m near Little Ouse
http://www.streetmap.co.uk/streetmap.dll?G2M?X=561500&Y=289705&A=Y&Z=3
Sheet 143 has lots of low value trigs.. a 0 and a 1m as well.
The number on the flush bracket has no meaning save to the OS, only
that the really important trigs (primary survey) are low numbers
c.1400 to 1600
There are sites out there run by trig fans with most of the numbers.
Richard Webb
Jim Ford
* with their presence by declaiming:
> - I settled for a trip to Scarba.
I've thought about visiting Scarba, as an alternative to Jura to see
Corrievrecken. Was the trip worth it?
Regards: Jim Ford
--
Spam poison - don't use! ---> bot...@watford53.freeserve.co.uk <---
John Brewer
>On Thu, 18 Sep 2003 16:33:31 +0000 (UTC),
>johnbrewer@naespam_compuserve.com (John Brewer) wrote:
>
>>I stumbled - metaphorically - across a trig point with a marked height
>>of 2m on the Scottish mainland - place called Rhunahaorine Point, just
>>opposite Ghigha (OS Landranger 62) and/or
>>
>>http://www.multimap.com/map/browse.cgi?X=169000&Y=650000&scale=25000
>>
>>The obvious questions are a) is there a lower one in the UK and, b) is
>>the height given the height of the brass plate or does it refer to
>>something else?
>>
>>...oh, and c) has this topic cropped up previously? If so, my
>>apologies....;-)
>
>
>Have a browse around the Angry Corrie website.......
>http://bubl.ac.uk/org/tacit/tac/tac53/frompill.htm
>2m is the lowest in Scotland, there is another 2m one near Beauly.
>http://www.streetmap.co.uk/streetmap.dll?G2M?X=255670&Y=847730&A=Y&Z=3
>A group visited your example at one of th Marilyn bagging conventions
>- I settled for a trip to Scarba.
Thanks for the references.
I'm intending to be cycling up there in a couple of weeks so might
call and pay a visit - just hope the tide's out and and/or there's an
offshore breeze...;-)
>I once visited a 6m one on Lady Isle, just off Troon.
>The lowest in Britain is in the Fens.. at -1m near Little Ouse
>http://www.streetmap.co.uk/streetmap.dll?G2M?X=561500&Y=289705&A=Y&Z=3
>Sheet 143 has lots of low value trigs.. a 0 and a 1m as well.
>The number on the flush bracket has no meaning save to the OS, only
>that the really important trigs (primary survey) are low numbers
>c.1400 to 1600
-1 m ? Sounds like some viewpoint!
>There are sites out there run by trig fans with most of the numbers.
Uh, oh - surely that can't be a healthy passtime, can it?
John B
RJ Webb
wrote:
>* RJ Webb <gri...@hellorobot.crux.u-net.com> deigned to grace uk.rec.walking
>* with their presence by declaiming:
>
>> - I settled for a trip to Scarba.
>
>I've thought about visiting Scarba, as an alternative to Jura to see
>Corrievrecken. Was the trip worth it?
Well its a lot smaller than Jura, but the hill is a very fine
quartzite peak and well worth the ascent. There s also the nice
feeling you get from visiting somewhere unusual....
Richard Webb
Graham Seed
"John Brewer" <johnbrewer@naespam_compuserve.com> wrote
> The obvious questions are a) is there a lower one in the UK and, b)
is
> the height given the height of the brass plate or does it refer to
> something else?
>
The height is to the bench mark. I've got a nice brass one on my fire
place hacked out of a trig that became redundant - G2118 which I
presume means geodetic or fairly important. I've got a book on these
things somewhere but it's packed away at the bottom of a box due to an
imminent house move!
Graham
Bryan Hall
floodplain that's under water for a couple of months each year.. and let's
not mention the parrot ...
--
Bryan
Dorzet
"John Brewer" <johnbrewer@naespam_compuserve.com> wrote in message
news:3f69de06....@news.btopenworld.com...
Jim Ford
* with their presence by declaiming:
>>> - I settled for a trip to Scarba.
> >
> >I've thought about visiting Scarba, as an alternative to Jura to see
> >Corrievrecken. Was the trip worth it?
>
> Well its a lot smaller than Jura, but the hill is a very fine
> quartzite peak and well worth the ascent. There s also the nice
> feeling you get from visiting somewhere unusual....
Did you get a good view of the Corrievrecken tide race? How did you get to
the island? Can you camp there and is there fresh water?
Ian Dainty
news:bkd4q6$4mr$1...@newsg1.svr.pol.co.uk
> The height is to the bench mark. I've got a nice brass one on my fire
> place hacked out of a trig that became redundant - G2118 which I
> presume means geodetic or fairly important. I've got a book on these
> things somewhere but it's packed away at the bottom of a box due to an
> imminent house move!
>
> Graham
Really? So they caught up with you at last! Where you off to?
S'not N*****y is it?
Worried regards,
Ian.
--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Graham Seed
"Ian Dainty" <jeff_...@hotmail.com> wrote
> Really? So they caught up with you at last! Where you off to?
Ohhhh, about 200yds up the road for about 6 months and then another
move about 20yds back down the road. I shall end up about 50 yds
closer to the pub if it all works out ok :-)) Anyway, I'll get rid of
this bloody freeserve addy which is being bombarded with spam and
stuff the puter in a bag for a while. Might actually get out and do
some walking for a change.........I'll see if I can find Rhyll Oil!
> S'not N*****y is it?
Isn't that expedition 15?
G
RJ Webb
wrote:
>* RJ Webb <gri...@hellorobot.crux.u-net.com> deigned to grace uk.rec.walking
>* with their presence by declaiming:
>
>>>> - I settled for a trip to Scarba.
>> >
>> >I've thought about visiting Scarba, as an alternative to Jura to see
>> >Corrievrecken. Was the trip worth it?
>>
>> Well its a lot smaller than Jura, but the hill is a very fine
>> quartzite peak and well worth the ascent. There s also the nice
>> feeling you get from visiting somewhere unusual....
>
>Did you get a good view of the Corrievrecken tide race?
No, Clag, but saw some interesting swirls at sea on the way in and
out.
>How did you get to
>the island?
Gemini sea taxi Crinan. Difficult Landing on the Corrievreckan
shore. The farm has a proper landing place.
> Can you camp there and is there fresh water?
Plenty of water, and a lot of the island is wild enough, may be a
useful courtesy to contact the folk on the farm first. (Scarba is
inhabited)
See Haswell Smith for details.
http://www.amazon.co.uk/exec/obidos/ASIN/0862415799/202-5517963-9907853
Richard Webb
RJ Webb
<bryan.ha...@ntlworld.com> wrote:
>It may not officially be the lowest - but there's one on the Christchurch
>floodplain that's under water for a couple of months each year.. and let's
>not mention the parrot ...
Christchurch and Chichester are famed for having numerous single digit
trigs
Richard Webb
RJ Webb
I have taken the liberty of reposting this on the trig point
enthusiasts newsgroup... There's often a lot of speculation as to trig
point vandals, should solve one mystery.
Richard Webb
Simon Edwardes
UK? I believe its somewhere around Holme Fen at -3m, but that's all I
could find on the web.
Cheers, Simon
(website: http://www.simonedwardes.co.uk - The Mountains of England
and Wales)
Richard Webb wrote: >
> The lowest (trig pillar) in Britain is in the Fens.. at -1m near Little Ouse
> http://www.streetmap.co.uk/streetmap.dll?G2M?X=561500&Y=289705&A=Y&Z=3
>
Paul Saunders
> Does anyone know the exact grid ref for the lowest (land) point in the
> UK? I believe its somewhere around Holme Fen at -3m, but that's all I
> could find on the web.
The land around the coast in these parts gets much lower than that,
twice every day!
The highest tides around here are 13m above mean sea level, so I presume
they drop to -13m below mean sea level too.
Paul
--
http://www.wilderness-wales.co.uk
http://www.photosig.com/go/users/userphotos?id=118749
John Laird
<pv...@wildwales.fsnet.co.uk> wrote:
>Simon Edwardes wrote:
>
>> Does anyone know the exact grid ref for the lowest (land) point in the
>> UK? I believe its somewhere around Holme Fen at -3m, but that's all I
>> could find on the web.
>
>The land around the coast in these parts gets much lower than that,
>twice every day!
>
>The highest tides around here are 13m above mean sea level, so I presume
>they drop to -13m below mean sea level too.
I think you'll find that the 13m is the tidal *range* (and from that I would
conclude you are in the Bristol Channel), so just over 6m above and below
MSL. Still very large (second in the world, iirc), but not as large as you
claim...
Also, strictly speaking, "land" stops at mean high water. However, IANAL
and all that !
--
John
Graham Seed
"RJ Webb" <gri...@hellorobot.crux.u-net.com> wrote in
> >>
> >The height is to the bench mark. I've got a nice brass one on my
fire
> >place hacked out of a trig that became redundant - G2118 which I
> >presume means geodetic or fairly important. I've got a book on
these
> >things somewhere but it's packed away at the bottom of a box due to
an
> >imminent house move!
> >
> >Graham
>
>
> I have taken the liberty of reposting this on the trig point
> enthusiasts newsgroup... There's often a lot of speculation as to
trig
> point vandals, should solve one mystery.
>
Cheers mate! ;-)
Trig points are of course, on private property, and sometimes the
owner might want rid and give it a nudge with his tractor. That means
it's useless and basically just good for scrap. However, the Spider
and the Flush Bracket are extremely difficult to get out, so you have
to be pretty determined to get at them. Me and my colleague tried to
get the Spider off the top of one local trig that had been turned on
its side after an *accident* and it took us about 3 visits to chip it
off, after which it was presented to another colleague who was
retiring!
When you've worked for the OS as long as we have, and between the
three of us we had well over 100 years, you get to feel a certain
ownership! We had to laugh once though when a member of the public
returned a brick to us with a bench mark cut on it.......*does this
belong to you?* :-))
Graham
John Brewer
>The height is to the bench mark.
Is this the brass plate on the top where they mount the theodothingy?
>I've got a nice brass one on my fire
>place hacked out of a trig that became redundant - G2118 which I
>presume means geodetic or fairly important.
Er, should you be broadcastling this to the wider world, or is it all
above board?...;-)
John B
Paul Saunders
> I think you'll find that the 13m is the tidal *range* (and from that
> I would conclude you are in the Bristol Channel), so just over 6m
> above and below MSL. Still very large (second in the world, iirc),
> but not as large as you claim...
But both of my tide table booklets talk about the "height" of the tide,
not the "range". My Swansea booklet list the "heights" of the tides and
to quote my West Wales booklet, in the section entitled - Heights of
Tides - it says; "For example, the evening high tide for Milford Haven
for Tuesday 18th February reaches a maximum height of 7.1 metres at
7.35pm."
So if these are the heights of the tides, what are they measured above?
Mean sea level, mean low water? The "height" of low water is constantly
changing so is the "height" of the tide measured against a constantly
changing value? The height of low water will be different on each side
of the same high tide.
Paul
> Also, strictly speaking, "land" stops at mean high water. However,
> IANAL and all that !
Having spent a lot of time walking on rocks and beaches around the Gower
coast during low tides, I'd have to disagree with you on that! :-)
Graham Seed
>
> >The height is to the bench mark.
>
> Is this the brass plate on the top where they mount the
theodothingy?
No, that's the *spider* (sp?) where normal obs are taken. These days
probably with GPS equipment. The height is taken to the bench mark
(Flush Bracket) on the side of the trig, if it has one. Otherwise
there is no real link with heighting as Trigs provided the horizontal
framework and BMs the vertical framework for mapping.
>
> >I've got a nice brass one on my fire
> >place hacked out of a trig that became redundant - G2118 which I
> >presume means geodetic or fairly important.
>
> Er, should you be broadcastling this to the wider world, or is it
all
> above board?...;-)
>
Probably not seeing as Richard's passed me on to the trig police! But
yes, I wouldn't dream of vandalising a Trig pillar. Trig maintenence
is/was part of my job with the OS, so any *spoils* that could be had
on the very rare occasion when we came across one that had been
destroyed were cherished. BTW, the afore mentioned FB was passed on to
me by my boss, rest his soul. It's still in the *family*.
Graham
Edward Fryer
"Paul Saunders" <pv...@wildwales.fsnet.co.uk> wrote in message
news:bkfc29$dvi$1...@news8.svr.pol.co.uk...
> But both of my tide table booklets talk about the "height" of the tide,
> not the "range". My Swansea booklet list the "heights" of the tides and
> to quote my West Wales booklet, in the section entitled - Heights of
> Tides - it says; "For example, the evening high tide for Milford Haven
> for Tuesday 18th February reaches a maximum height of 7.1 metres at
> 7.35pm."
>
> So if these are the heights of the tides, what are they measured above?
> Mean sea level, mean low water? The "height" of low water is constantly
> changing so is the "height" of the tide measured against a constantly
> changing value? The height of low water will be different on each side
> of the same high tide.
>
> Paul
For tide tables, and in fact for all nautical publications: charts, pilot
books etc, the reference point for tidal heights is LAT - the Lowest
Astronomical Tide. This is the lowest tide seen with no extraneous factors:
for example, tide heights can be higher in periods of low pressure, and
lower in periods of high pressure. Also, long periods of wind from one
direction can change the heights.
Tide tables should give you four times and four heights per day. Two high
waters, together with the height of the high water, and the two times of low
water together with the height of low water. The difference between high and
low water is the range.
Twice each month you get large tides - springs - which are roughly when the
sun and the moon line up, and twice each month the tidal range hits a
minimum - neaps, when the sun and moon are at roughly 90 degrees.
John Laird
<pv...@wildwales.fsnet.co.uk> wrote:
>> Also, strictly speaking, "land" stops at mean high water. However,
>> IANAL and all that !
>
>Having spent a lot of time walking on rocks and beaches around the Gower
>coast during low tides, I'd have to disagree with you on that! :-)
I think it goes: land, (fore-)shore, sea-bed. The Crown owns, by default,
the fore-shore. For sure ;-)
--
John
Paul Saunders
> For tide tables, and in fact for all nautical publications: charts,
> pilot books etc, the reference point for tidal heights is LAT - the
> Lowest Astronomical Tide.
Thanks for that info.
> Tide tables should give you four times and four heights per day. Two
> high waters, together with the height of the high water, and the two
> times of low water together with the height of low water. The
> difference between high and low water is the range.
Ah, now my local Swansea tide tables only give the times and heights of
high tide. However my West Wales booklet does give the low tides too,
but they are for Milford Haven, where the range is much smaller. I
notice that the lowest tide I can find this year at Milford is 0.1m, so
that seems to tied in with what you are saying abut the LAT. Pity the
Swansea booklet doesn't list this information also.
If the LAT at Milford is 0.0m, then would it also be 0.0m at Swansea at
the same time, even though the Swansea tide would actually be lower
since the range is larger here?
Paul Saunders
> I think it goes: land, (fore-)shore, sea-bed. The Crown owns, by
> default, the fore-shore. For sure ;-)
So no-else owns it? So it's okay for me to camp on the fore-shore then?
Pat Bennett
I'm not at all sure what the "height" in your tide table booklet
means. The tide tables which I consult regularly enable me to get out
to Hilbre Island in the Dee estuary, and they are at
http://www.nbi.ac.uk/appl/liverpool.html. They quote the height at
high tide, and the height at low tide - both positive quantities.
However, the info sheet says that the datum=chart datum: 4.93 metres
below Ordnance Datum (Newlyn).
So - should you be subtracting a datum from your "maximum height of
7.1 metres at 7.35pm"?
Pat
Pat Bennett
From Cheshire in the UK
www.cheshirewildlife.co.uk
John Laird
<pv...@wildwales.fsnet.co.uk> wrote:
>John Laird wrote:
>
>> I think it goes: land, (fore-)shore, sea-bed. The Crown owns, by
>> default, the fore-shore. For sure ;-)
>
>So no-else owns it? So it's okay for me to camp on the fore-shore then?
No, it *can* be privately owned, as I understand things. Otherwise, it
belongs to Liz. (Hence the "by default" bit.) I don't know her feelings on
you camping there, but by definition twice per day you will get wet...
--
John
Martin Richardson
<r...@gseed.freeserve.co.uk> writes
>
>>
>Probably not seeing as Richard's passed me on to the trig police! But
>yes, I wouldn't dream of vandalising a Trig pillar. Trig maintenence
>is/was part of my job with the OS, so any *spoils* that could be had
>on the very rare occasion when we came across one that had been
>destroyed were cherished. BTW, the afore mentioned FB was passed on to
>me by my boss, rest his soul. It's still in the *family*.
>
When?
Were they cast on site or transported to the summits whole?
How?
How long did it all take?
Anyone die in the process?
How was it decided where to put them?
Why are the trig points in Republic of Ireland of exactly the same
construction?
--
Martin Richardson
216/284 Munros (34/34 'Furths')
27/89 Donalds 377/1552 Marilyns 439/439 Nuttalls
Stuart Baldwin
<mar...@thequiff.demon.co.uk> wrote:
>Why are the trig points in Republic of Ireland of exactly the same
>construction?
I think it very likely that the originals were built by the same
people that built the ones this side of the water.
Graham Seed
"Martin Richardson" <mar...@thequiff.demon.co.uk> wrote
> So who built them? Royal Engineers?
> When? Long time ago
> Were they cast on site or transported to the summits whole? built on
site methinks
> How? Lug the stuff up to the top of the mountain
> How long did it all take? Years.....
> Anyone die in the process? probably
> How was it decided where to put them? powerful light at night?
numerous recces....
> Why are the trig points in Republic of Ireland of exactly the same
> construction? We were one country for a looooooong time.
Please don't make me get my book out, it's at the bottom of about ten
boxes.......
Graham
Paul Saunders
> I'm not at all sure what the "height" in your tide table booklet
> means. The tide tables which I consult regularly enable me to get out
> to Hilbre Island in the Dee estuary, and they are at
> http://www.nbi.ac.uk/appl/liverpool.html. They quote the height at
> high tide, and the height at low tide - both positive quantities.
Yes, they usually will be. As Edward pointed out, "the reference point
for tidal heights is LAT - the Lowest Astronomical Tide." So if the
lowest possible tide is zero, most of the time low tide will be higher
than that. If you look at September 28th on your Liverpool tide page
you'll see that there's a low tide of just 0.27m, which is just slightly
above zero, one of the lowest tides this year.
> However, the info sheet says that the datum=chart datum: 4.93 metres
> below Ordnance Datum (Newlyn).
>
> So - should you be subtracting a datum from your "maximum height of
> 7.1 metres at 7.35pm"?
I shouldn't think so. The height of sea level is different all around
the coast. We've covered this before during GPS discussions. In spite
of the name, the sea isn't level. :-)
The height of sea level at Newlyn is simply a reference point, a
baseline. At Liverpool, sea level is 4.93m lower than at Newlyn, but
it's still sea level. At Swansea it's 2.8m below.
Paul Saunders
>> So no-else owns it? So it's okay for me to camp on the fore-shore
>> then?
>
> No, it *can* be privately owned, as I understand things. Otherwise,
> it belongs to Liz. (Hence the "by default" bit.) I don't know her
> feelings on you camping there, but by definition twice per day you
> will get wet...
Nope, not if you do it during a neap tide (especially in an area like
the Bristol Channel with such a high tidal range). High tides often
don't reach the high tide mark around here, it's fairly uncommon for the
tide to come all the way in at Swansea Bay.
And yes, in case you're wondering, I have camped below the high tide
mark, at Oxwich Bay.
Edward Fryer
> Ah, now my local Swansea tide tables only give the times and heights of
> high tide. However my West Wales booklet does give the low tides too,
> but they are for Milford Haven, where the range is much smaller. I
> notice that the lowest tide I can find this year at Milford is 0.1m, so
> that seems to tied in with what you are saying abut the LAT. Pity the
> Swansea booklet doesn't list this information also.
>
> If the LAT at Milford is 0.0m, then would it also be 0.0m at Swansea at
> the same time, even though the Swansea tide would actually be lower
> since the range is larger here?
Not necessarily. AIUI, the shape of the coast has significant effect upon
tidal heights and times. Just because there is a tidal range of x in one
port doesn't necessarily mean that the tidal range will also be x at the
port down the coast. Of a similar order of magnitude, but not necessarily
the same.
In order for the hydrographic office not to have to produce tide tables for
every single harbour in the country, what they do is calculate them for
significant ports (I have a mental blockage, and can't remeber the precise
term: primary port rings a bell, but I can't guarantee it). To calculate
tide times at smaller harbours, you have a table which gives the offset to
the primary port. For instance, it may say that at neaps, high water at
secondary port B is 30 mins after primary port A, and 20 cm lower, but at
springs it is 30 mins before. Secondary port calculations are one of the fun
things to learn about navigating boats.
-Edward
Paul Saunders
>> If the LAT at Milford is 0.0m, then would it also be 0.0m at Swansea
>> at the same time, even though the Swansea tide would actually be
>> lower since the range is larger here?
>
> Not necessarily. AIUI, the shape of the coast has significant effect
> upon tidal heights and times. Just because there is a tidal range of
> x in one port doesn't necessarily mean that the tidal range will also
> be x at the port down the coast. Of a similar order of magnitude, but
> not necessarily the same.
No, that's not what I meant. The range is much higher at Swansea, it's
13m at King's Dock, Swansea, but only 7.6m at Milford Haven. I mean is
the LAT at Swansea calibrated to 0m? Even though the heights of low
tide would differ, the high tides would still be measured relative to
them, therefore the lowest tides would still be called 0m, yes?
> In order for the hydrographic office not to have to produce tide
> tables for every single harbour in the country, what they do is
> calculate them for significant ports (I have a mental blockage, and
> can't remeber the precise term: primary port rings a bell, but I
> can't guarantee it). To calculate tide times at smaller harbours, you
> have a table which gives the offset to the primary port. For
> instance, it may say that at neaps, high water at secondary port B is
> 30 mins after primary port A, and 20 cm lower, but at springs it is
> 30 mins before. Secondary port calculations are one of the fun things
> to learn about navigating boats.
Yeah, well I suppose that Swansea must be a primary port. I used to
have fun trying to calculate the exact moment of low tide on the Gower
Peninsula when wandering over the rocks to get to inaccessable places
like sea-caves and suchlike. It wasn't easy to do since the next port
along the coast is Llanelli which has a strange offset since it's up an
estuary. I'm sure I worked it out, but I can't remember what it is now
though.
Dominic Sexton
<r...@gseed.freeserve.co.uk> writes
>
Go on, you know you want to...
--
Dominic Sexton
http://www.dscs.demon.co.uk/
W. D. Grey
<jo...@laird-towers.org.uk> writes
>>Having spent a lot of time walking on rocks and beaches around the Gower
>>coast during low tides, I'd have to disagree with you on that! :-)
>
>I think it goes: land, (fore-)shore, sea-bed. The Crown owns, by default,
>the fore-shore. For sure ;-)
That S-'andy info
--
Bill Grey
http://www.billboy.co.uk
John Brewer
>It may not officially be the lowest - but there's one on the Christchurch
>floodplain that's under water for a couple of months each year.. and let's
>not mention the parrot ...
This may be a hot new topic, then: The Most Inaccessible Trig Point
in the UK...
....oh, and I never mentioned a pa......
John B
John Brewer
> Twice each month you get large tides - springs - which are roughly when the
>sun and the moon line up, and twice each month the tidal range hits a
>minimum - neaps, when the sun and moon are at roughly 90 degrees.
I've never quite understood why there are *two* tides each day. I'm
familiar with the text book diagram that show shows 'bulges' of water
- one on the same side of the Earth as the Sun, and the other on the
opposite side.
What I don't understand is why there isn't just *one* bulge on
whichever side the water feels like going to....
...oops, prepare to duck for cover....;-)
John B
Paul Rooney
johnbrewer@naespam_compuserve.com (John Brewer) wrote:
>
>I've never quite understood why there are *two* tides each day.
http://www.math.nus.edu.sg/aslaksen/teaching/hm/tides.shtml
--
Paul
My Lake District walking site:
http://paulrooney.netfirms.com
108 Wainwrights
Please sponsor me for the London Marathon at:
http://www.justgiving.com/london2004
Martin Richardson
<{d-sep03}@dscs.demon.co.uk> writes
John Brewer
>>I've never quite understood why there are *two* tides each day.
>http://www.math.nus.edu.sg/aslaksen/teaching/hm/tides.shtml
I just *knew* this wasn't going to be easy...;-)
I think I'll need to sit down with a large glass of something cold and
study the fisiks...
John B
David Laight
http://www.streetmap.co.uk/newmap.srf?x=561645&y=289745&z=3&ar=Y
Not been to see if it is still there though....
David
Edward Fryer
> Edward Fryer wrote:
>
> >> If the LAT at Milford is 0.0m, then would it also be 0.0m at Swansea
> >> at the same time, even though the Swansea tide would actually be
> >> lower since the range is larger here?
> >
> > Not necessarily. AIUI, the shape of the coast has significant effect
> > upon tidal heights and times. Just because there is a tidal range of
> > x in one port doesn't necessarily mean that the tidal range will also
> > be x at the port down the coast. Of a similar order of magnitude, but
> > not necessarily the same.
>
> No, that's not what I meant. The range is much higher at Swansea, it's
> 13m at King's Dock, Swansea, but only 7.6m at Milford Haven. I mean is
> the LAT at Swansea calibrated to 0m? Even though the heights of low
> tide would differ, the high tides would still be measured relative to
> them, therefore the lowest tides would still be called 0m, yes?
>
AIUI, it's not really "calibrated" to anything. If you look at a nautical
chart, you'll see that it's covered in numbers: the depth water. Every one
of these numbers relates to the depth of water at that particular point
below chart datum: with, as we have said, chart datum being the LAT. To find
the actal depth of water for a particular time of day, you have to calculate
the depth of tide at that time, and add it to the depth of water shown on
the chart. The idea is that (subject to atmospheric conditions), you'll
never get less water than that shown on the chart, so you know whether you
can sail somewhere or not.
Basically, chart datum is chart datum.
In both places, the tide tables will give you heights of tides above chart
datum. What the relative heights of the datums are in the different places,
well, I have no idea. What on earth do you measure relative to?
NC
"RJ Webb" <gri...@hellorobot.crux.u-net.com> wrote in message
news:3f69e50...@news-text.blueyonder.co.uk...
> On Thu, 18 Sep 2003 16:33:31 +0000 (UTC),
> johnbrewer@naespam_compuserve.com (John Brewer) wrote:
> The lowest in Britain is in the Fens.. at -1m near Little Ouse
> http://www.streetmap.co.uk/streetmap.dll?G2M?X=561500&Y=289705&A=Y&Z=3
>
> Sheet 143 has lots of low value trigs.. a 0 and a 1m as well.
Can I introduce readers to the Suffolk Bottoms ? This is a round (like the
Lakes 3000') of "high" points and trig pillars near the Suffolk coast. It
involves visiting all the sub-30m trig points in Suffolk. The "highlights"
include a field near Bawdsey at 0m and the dizzy top of Dunwich cliffs with
a sheer drop of 22m.
Its a rather long walk, though does make a pleasant days cycle. A little
over 60 miles if you use the train for the return leg. Two ferry crossings
(a bit deep to wade :-), one is dredged for container ships).
Nigel
Graham Seed
"Martin Richardson" <mar...@thequiff.demon.co.uk> wrote
> >
> >
> I would very much like to read the book. Is it available through
Amazon?
>
> --
might I can't find the damn thing. It is a history of the OS up to the
70s so will include the likes of levelling, but misses out on modern
technology. There is another copy in the office though, so I'll let
you have some more info tomorrow.
G
Martin Richardson
<r...@gseed.freeserve.co.uk> writes
>
vector mapping etc. I want to know about the pioneers. I've got Colonel
Sir Charles Close's 'The early years of the Ordnance Survey' - but it
leaves you with more questions than answers.
Seems to me there is a gap in the market for a popular science type book
that someone like Simon Winchester, Nicholas Crane or Dava Sobel should
write.
Maybe I should write it and knock Beckham off the top of the
bestseller's list.
RJ Webb
>Why are the trig points in Republic of Ireland of exactly the same
>construction?
Are they?
Some near the border are, but a lot of the southern ones seem quite
modern, they looked brand new when I first started walking in Ireland
with very different brass work.
The Greek ones look superficially like ours but again without the
heavyduty brass. I donk know about the internal structure....
Richard Webb
RJ Webb
>
>Can I introduce readers to the Suffolk Bottoms ? This is a round (like the
>Lakes 3000') of "high" points and trig pillars near the Suffolk coast. It
>involves visiting all the sub-30m trig points in Suffolk. The "highlights"
>include a field near Bawdsey at 0m and the dizzy top of Dunwich cliffs with
>a sheer drop of 22m.
>
>Its a rather long walk, though does make a pleasant days cycle. A little
>over 60 miles if you use the train for the return leg. Two ferry crossings
>(a bit deep to wade :-), one is dredged for container ships).
>
The folks at The Angry Corrie would love to hear about this......
Sounds a great wheeze
Richard Webb
RJ Webb
>Trig points are of course, on private property, and sometimes the
>owner might want rid and give it a nudge with his tractor.
Dungavel Hill, Lanarkshire, seems to have been given a nudge by a
scratching bovine, judging by the evidence around the remains
Richard Webb
RJ Webb
johnbrewer@naespam_compuserve.com (John Brewer) wrote:
>"Bryan Hall" <bryan.ha...@ntlworld.com> wrote:
>
>>It may not officially be the lowest - but there's one on the Christchurch
>>floodplain that's under water for a couple of months each year.. and let's
>>not mention the parrot ...
>
>This may be a hot new topic, then: The Most Inaccessible Trig Point
>in the UK...
Managed two in Porton Down, and during the trip a lot was mentioned
about one in a secure water board establishment in Coreley
Warwickshire.
There are several inside secure naval bases as well.
Some of the island ones can be fun....
Richard Webb
RJ Webb
The -1m was there last winter according to a correspondant in the rhb
group.
Richard Webb
NC
>
> >
> >Can I introduce readers to the Suffolk Bottoms ? This is a round (like
the
> >Lakes 3000') of "high" points and trig pillars near the Suffolk coast.
It
> >involves visiting all the sub-30m trig points in Suffolk. The
"highlights"
> >include a field near Bawdsey at 0m and the dizzy top of Dunwich cliffs
with
> >a sheer drop of 22m.
> The folks at The Angry Corrie would love to hear about this......
> Sounds a great wheeze
Perhaps I'll write it up, though would need a change of journal title - "The
Miffed Barrow" might do it.
Nigel
Simon Edwardes
know the exact grid ref for the lowest (land) point in the UK?".
Cheers, Simon ;-)
RJ Webb
Edwardes) wrote:
>So to rephrase my question, "Does anyone (apart from Paul and co.)
>know the exact grid ref for the lowest (land) point in the UK?".
I doubt anyone does... The Fens are shrinking with all the pumping and
intensive agriculture. As the LP is an area rather than an antipeak
any GR is going to be approx.
The bible on these matters is Hutchison...
http://bubl.ac.uk/org/tacit/tables/world.html
and a copy is never far from my terminal
Great Britain and Northern Ireland: HP some lump near the Mamores
1344m 56.48N 5.01W
LP: Holme Fen -3m 52.29N 0.12W
Streetmap and getamap suggests the following GR
TL 223 888
Getamap 1:25000 has a -2m spot and a tiny sealevel contour ring. Quite
a bag!
http://www.streetmap.co.uk/streetmap.dll?G2M?X=522331&Y=288790&A=Y&Z=3
Richard Webb
Simon Challands
gri...@hellorobot.crux.u-net.com (RJ Webb) wrote:
That varies with ours, anyway. They seem to be built from whatever was
available nearby (if anything), which is why some are stone and others seem
more concrete.
--
Simon Challands, creator of
The Acorn Elite Pages: http://elite.acornarcade.com/
Three Dimensional Encounters: http://www.3dfrontier.fsnet.co.uk/
Graham Seed
"Martin Richardson" <mar...@thequiff.demon.co.uk> wrote in message
news:Y9twOTEqffb$Ew...@thequiff.demon.co.uk...
> In article <bkkii5$uk5$1...@newsg3.svr.pol.co.uk>, Graham Seed
> <r...@gseed.freeserve.co.uk> writes
> >
> >"Martin Richardson" <mar...@thequiff.demon.co.uk> wrote
> >> >
> >> >
> >> I would very much like to read the book. Is it available through
> >Amazon?
> >>
> >> --
> >Possibly, but my copy is hidden in several boxes of books and try
as I
> >might I can't find the damn thing. It is a history of the OS up to
the
> >70s so will include the likes of levelling, but misses out on
modern
> >technology. There is another copy in the office though, so I'll let
> >you have some more info tomorrow.
> >
> >G
> >
> >
> Just what I want. I'm not interested in all the new-fangled stuff
about
> vector mapping etc. I want to know about the pioneers. I've got
Colonel
> Sir Charles Close's 'The early years of the Ordnance Survey' - but
it
> leaves you with more questions than answers.
>
written by J B Harley, but doesn't have an IBN number. It seems to
have been published by a combination of HMSO/OS and Oxford press so
it will probably be out of print now and found only in the bottom
cardboard box in my living room ;-)
I hoped it would have a better section on Trig building, but it
concentrates more on the mapping scales and how they evolved, with
good sections on Levelling, Projections and National Grid. Early on it
mentions the Irish Survey, which specified a scale of 1:10560 as early
as 1824 for land taxation purposes. As trig design is fairly basic,
one could assume that there wasn't much evolvement to designs used
then and now, so perhaps that's why British and Irish trigs have a
similarity. As to who built them, well the Principal Triangulation
(Pub 1858) was a selection of data from the mass of observations made
earlier, so pillars must have been built before that time. The
Retriangulation, which formed the basis of todays mapping was done
between 1935 and 1962, so either new pillars would have been built, or
old pillars would have been checked/maintained/rebuilt by Trig
maintenance teams who would have had their roots in the army.
Don't forget, the trig point is not the top of the pillar but a bolt
on the bed rock over which the pillar is built - just thought I'd
throw that one in there. Not all pillars are built to the traditional
design of course (Bruach na Frithe - cylindrical design and does it
have a flush bracket?)
Going back to a previous point - the height given on a small scale map
is to the base of a pillar. A Pillar that has a Flush Bracket on the
side will have been spirit livelled to ( one presumes - there is some
talk of trig levelling in the book, but to no great accuracy - approx
2ft) and the bench mark will be heighted to centimetres. But for
general info on walking maps heighting will be given to the nearest
metre. A pillar may not be at the summit of a hill of course. In the
book it describes how Scafell Pike was attributed its height.
Previously, it had been given a height of 3210 ft. The base of the
trig was established at 3206 ft:
*....Scafell Pike, for example is covered by a large cairn with a war
memorial plaque set into it, ground height at the base of the cairn
was determined as 3209 ft, and, as it was reasonable to assume that
additional height existed beneath the cairn, the descision to leave
the old summit height of 3210 ft undisturbed was justified.
G