GPS?

On 9 Nov, 22:53, "Martin Bulmer" <[email hidden]>

Quoted message said:

does anyone know if these GPS devices can translate
latitude & longitude to OS?

For most hand-held GPS units the answer is yes. However if its the
cycle computer/GPS combo Garmin Edge 205 or 305, the answer is no.

SW

On 9 Nov,

Martin Bulmer said:

If so, does anyone know if these GPS devices can translate
latitude & longitude to OS?

Mine (Magellan Explorist 200) can be set to do either. I would think others
will be the same.

--
BD
Change lycos to yahoo to reply

Martin Bulmer said:

It does this by latitude & longitude. Does anyone
know if that would be any use to an ambulance crew, or do they need O.S.
map references? If so, does anyone know if these GPS devices can translate
latitude & longitude to OS? Please tell me they do, cos now I've played with
one, I want one anyway.

If you call the emergency services, give them your lat and longitude
from the GPS, they can then enter it into their own GPS units, and the
unit will guide them to you, taking an extra twenty minutes.

If they don't have GPS, it is just a quick look on the web, or a call to
the coast guard to get OS.

Martin.

Martin Bulmer said:

ambulance crew, or do they need O.S. map references? If so, does
anyone know if these GPS devices can translate latitude & longitude
to OS? Please tell me they do, cos now I've played with one, I want
one anyway.

My Garmin e-trex legend does.

Emergencies aside, I would always select one a GPS unit which did have OSGB
display for my own use as its easier for your own personal navigation when
used in conjuction with maps.

Alex
--
Mr R@T / General Lighting
Ipswich, Suffolk, Untied Kingdom
http://www.partyvibe.com

Martin Bulmer said:

Being the worrying kind, I've started wondering what would happen if a
cyclist needed to call an ambulance to an off-road position - it must
happen.

I recall a tale my dad once related to me: police had been called to a
(non urgent) incident. Where was it, sir? A GR was provided, but the
Met. didn't do GRs, could he say where it was in the A to Z?

Quoted message said:

tells you where you are. It does this by latitude & longitude. Does anyone
know if that would be any use to an ambulance crew, or do they need O.S.
map references?

Long/Lat on its own would be pretty hopeless. However, the only GPS
unit I've come across to date that only worked in Long/Lat was the first
ever Casio wrist mounted one, which is quite a while ago now. Most give
you a choice of numerous grids and datums so you can usefully use them
anywhere.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

in message <[email hidden]>, Martin Bulmer

(') said:

Being the worrying kind, I've started wondering what would happen if a
cyclist needed to call an ambulance to an off-road position - it must
happen. Those bike-mounted GPS things might help, I thought, so I checked
out the nearest bike shop that had them (60 mile round trip), and they
didn't know whether they would help or not, but they kindly let me play
with one, together with the instruction book. I found out how to measure
my heart rate, the distance travelled, speed etc, then finally found the
bit that tells you where you are. It does this by latitude & longitude.
Does anyone
know if that would be any use to an ambulance crew, or do they need O.S.
map references? If so, does anyone know if these GPS devices can
translate latitude & longitude to OS? Please tell me they do, cos now
I've played with one, I want one anyway.

Most GPS units sold in Britain can translate latitude/longitude to OS grid
units and vice versa. The algorithm is a total pig, but it's published and
is well known; I've implemented it myself. Also, the control room systems
can do this, even if your GPS can't.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; "If I were a Microsoft Public Relations person, I would probably
;; be sobbing on a desk right now" -- Rob Miller, editor, /.

Simon Brooke said:

Most GPS units sold in Britain can translate latitude/longitude to OS grid
units and vice versa. The algorithm is a total pig, but it's published and
is well known; I've implemented it myself.

Minor quibble - the approximate algorithm is published. The
millimetre-accuracy translation into OSGB is a proprietary secret
(it's an elastic sheet sort of thing) that costs lots from the OS
people.

However, if you've fallen off in the hills the ambulance bods probably
don't need the grid reference of the point in the bone which has
broken. The published (helmert) transformation will get you to within
a metre or so.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

Ian Smith said:

Simon Brooke said:

Most GPS units sold in Britain can translate latitude/longitude to OS grid
units and vice versa. The algorithm is a total pig, but it's published and
is well known; I've implemented it myself.

Minor quibble - the approximate algorithm is published. The
millimetre-accuracy translation into OSGB is a proprietary secret
(it's an elastic sheet sort of thing) that costs lots from the OS
people.

However, if you've fallen off in the hills the ambulance bods probably
don't need the grid reference of the point in the bone which has
broken. The published (helmert) transformation will get you to within
a metre or so.

regards, Ian SMith

--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Ian Smith said:

However, if you've fallen off in the hills the ambulance bods probably
don't need the grid reference of the point in the bone which has
broken. The published (helmert) transformation will get you to within
a metre or so.

As long as you've been careful: for my MSc. thesis I had to convert
between the two and I got to find out how very very big and very very
small numbers can get very very wrong in computed floating point
arithmetic, especially if it's VAX/VMS circa 1989... The conversion
broke the floating point implementation completely if you weren't quite
careful what order you did supposedly commutative operations in.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Ian Smith said:

However, if you've fallen off in the hills the ambulance bods probably
don't need the grid reference of the point in the bone which has
broken. The published (helmert) transformation will get you to within
a metre or so.

If he'd being wearing a helmert, he would hardly need to call the
emergency services, now would he?

Ian Smith said:

Simon Brooke said:

Most GPS units sold in Britain can translate latitude/longitude to OS grid
units and vice versa. The algorithm is a total pig, but it's published and
is well known; I've implemented it myself.

Minor quibble - the approximate algorithm is published. The
millimetre-accuracy translation into OSGB is a proprietary secret
(it's an elastic sheet sort of thing) that costs lots from the OS
people.

You used to be able to download a demo version of some software that
did the accurate transform. I think it was called GEOTRANS. I've got
a copy of it somewhere. There was a paper which described the method
too but I can't seem to find that either now.

Chris
--
Chris Eilbeck

Chris Eilbeck said:

You used to be able to download a demo version of some software that
did the accurate transform. I think it was called GEOTRANS. I've got
a copy of it somewhere. There was a paper which described the method
too but I can't seem to find that either now.

The current OS-approved software is Grid InQuest which is a free
download (registration required) from Quest:

<URL:http://www.qgsl.com/software/gridiq.php>

As well as a standalone application there is also a DLL available if
you want to incorporate the transformation algorithm into your own
software.

SW

Chris Eilbeck said:

You used to be able to download a demo version of some software that
did the accurate transform. I think it was called GEOTRANS. I've got
a copy of it somewhere. There was a paper which described the method
too but I can't seem to find that either now.

You might mean (all one url but I've split it at a readable place):

http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/
A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf

Which is interesting - last time I downloaded it section 6.3 said "...
is obtained by a bilinear transformation. This is called the National
Grid Transformation OSTN97, and it is available in software packages
from licensed third-party software developers."

Now it says: "... is obtained by a bi-linear interpolation. This is
called the National Grid Transformation OSTN02, and it is freely
available in software packages from the Ordnance Survey GPS website,
www.ordnancesurvey.co.uk/gps."

So it seems I was indeed wrong - it's no longer a proprietary
transform for wich you have to pay sums of money, but one you can
download for free. Apologies for the misinformation.

The geoid model transform (also updated to '02) seems to be free as
well now.

Other than those two changes, a quick skim doesn't reveal anything
significant has changed in the last several years since I last played
with the maths. If you're happy with 12-decimal-place iterative
arithmetic it's not difficult - I implemented it on a Psion handheld
to talk to my GPS some years ago.

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

in message <[email hidden]>, SW

(') said:

Chris Eilbeck said:

You used to be able to download a demo version of some software that
did the accurate transform. I think it was called GEOTRANS. I've got
a copy of it somewhere. There was a paper which described the method
too but I can't seem to find that either now.

The current OS-approved software is Grid InQuest which is a free
download (registration required) from Quest:

<URL:http://www.qgsl.com/software/gridiq.php>

As well as a standalone application there is also a DLL available if
you want to incorporate the transformation algorithm into your own
software.

Which is fine if you are a slavish victim of The Monopoly, but doesn't help
those of us who aren't. But, as I say, you can implement the algorithm
yourself.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; MS Windows: A thirty-two bit extension ... to a sixteen bit
;; patch to an eight bit operating system originally coded for a
;; four bit microprocessor and sold by a two-bit company that
;; can't stand one bit of competition -- anonymous

in message <[email hidden]>, Peter Clinch

(') said:

Martin Bulmer said:

tells you where you are. It does this by latitude & longitude. Does
anyone
know if that would be any use to an ambulance crew, or do they need
O.S. map references?

Long/Lat on its own would be pretty hopeless.

Why?

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; single speed mountain bikes: for people who cycle on flat mountains.

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

Quoted message said:

Being the worrying kind, I've started wondering what would happen
if a
cyclist needed to call an ambulance to an off-road position -

[snip]

I seem to recall hearing that the emergency services work by postcode
nowadays, which narrows things down to about a dozen houses. That
works quite well for most places, but apparently the postcode
containing the top of Snowdon covers quite a large area.

If you take a GPS to the Greenwich Observatory, you will find about a
101 metre discrepancy between the GPS's opinion about your longitude,
and the Observatory's. There's been some kind of European Union
effort to sort things out, and as a result of the standardisation
efforts the Observatory is now considered to be constantly moving,
although not very fast. I can't remember where it's moving to, nor
its speed.

Jeremy Parker

Jeremy Parker said:

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

Quoted message said:

Being the worrying kind, I've started wondering what would happen
if a
cyclist needed to call an ambulance to an off-road position -

[snip]

I seem to recall hearing that the emergency services work by postcode
nowadays, which narrows things down to about a dozen houses. That
works quite well for most places, but apparently the postcode
containing the top of Snowdon covers quite a large area.

If you take a GPS to the Greenwich Observatory, you will find about a
101 metre discrepancy between the GPS's opinion about your longitude,
and the Observatory's. There's been some kind of European Union
effort to sort things out, and as a result of the standardisation
efforts the Observatory is now considered to be constantly moving,
although not very fast. I can't remember where it's moving to, nor
its speed.

There are nine competing Prime Meridian's all of which pass close to
Greenwich. The differences are up to 200m.

Treaty originally defined the Prime Meridian by the cross hairs on the
eyepice of the Primary Transit Telescope at Greenwich.

For comprehensive details, click here.

[800Kb pdf download]
http://tinyurl.com/yftayo from
http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf

Martin Bulmer said:

Being the worrying kind, I've started wondering what would happen if a
cyclist needed to call an ambulance to an off-road position - it must
happen. Those bike-mounted GPS things might help, I thought, so I checked
out the nearest bike shop that had them (60 mile round trip), and they
didn't know whether they would help or not, but they kindly let me play with
one, together with the instruction book. I found out how to measure my heart
rate, the distance travelled, speed etc, then finally found the bit that
tells you where you are. It does this by latitude & longitude. Does anyone
know if that would be any use to an ambulance crew, or do they need O.S.
map references? If so, does anyone know if these GPS devices can translate
latitude & longitude to OS? Please tell me they do, cos now I've played with
one, I want one anyway.

Not really an answer to your question, but I wrote a blog piece (gaahhh
... never thought I'd say that) which helped him get going with some
bits and pieces with his new GPS ...

http://www.elyob.com/blog/

Jeremy Parker said:

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

Quoted message said:

Being the worrying kind, I've started wondering what would happen
if a
cyclist needed to call an ambulance to an off-road position -

Quoted message said:

[snip]

Quoted message said:

I seem to recall hearing that the emergency services work by postcode
nowadays, which narrows things down to about a dozen houses. That
works quite well for most places, but apparently the postcode
containing the top of Snowdon covers quite a large area.

Quoted message said:

If you take a GPS to the Greenwich Observatory, you will find about a
101 metre discrepancy between the GPS's opinion about your longitude,
and the Observatory's.

Only if you have set your GPS to a different datum than that used by
the Observatory. It's a good idea in the UK to set your GPS to the OS
datum. Many US made GPS devices are supplied by default with the
standard US datum, and many UK purchasers don't read the manual :-)

--
Chris Malcolm [email hidden] DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]