GPS accuracy

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

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard

slog

Quoted message said:

for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Surely this cannot be right?

Rory

I checked another site and it says that The Ben is 3194ft.

http://www.aboutbritain.com/BenLomond.htm
versus
http://www.b-mercer.demon.co.uk/benl.htm

I think Bens figures are way off the mark.

Rory

Rodders said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard slog
for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Surely this cannot be right?

No, it isn't.

I make Ben Lomond 974 m (according to OS map) and TACit Tables give
that as 3195 feet.

What I find surprising is that the GPS altitude is almost spot on. I
find it usually reads 10 m (30 feet) over.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

In article <[email hidden]>, Phil Cook
<[email hidden]> writes

Quoted message said:

Rodders said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard slog
for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Surely this cannot be right?

No, it isn't.

I make Ben Lomond 974 m (according to OS map) and TACit Tables give
that as 3195 feet.

What I find surprising is that the GPS altitude is almost spot on. I
find it usually reads 10 m (30 feet) over.

I seem to remember you are using a GPS12 Phil. Garmins of that vintage
over read by about 10m in the UK. This is due to the table inside them
of altitude (Geoid) corrections being in error by about 10m. The eTrex
series and later have more accurate values.

When the 12 etc. came out nobody noticed this error because SA was alive
and kicking.

--

Dominic Sexton
http://www.dscs.demon.co.uk/

Phil Cook said:

What I find surprising is that the GPS altitude is almost spot on. I
find it usually reads 10 m (30 feet) over.

That's with the older models. Are you still using a 12? The newer
models have been corrected to take this error into account.

Having said that, I still occasionally get GPS altitude readings as much
as 10m over, although not often. Haven't seen it 10m under yet, but
have seen it 5-6m lower. Generally it's in the correct vicinity.

With the altimeter though, I usually see the altimeter reading, not the
GPS reading. They've made it awkward to access the GPS altitude, it can
be done but it's not constantly on display. On the few occasions that I
check, it's usually up to 5m or so out, whereas the barometric altitude
is almost always within 2m.

Having determined my home altitude very precisely, or more specifically
my car parking spot, I always begin every journey by attaching my GPS to
the dashboard mount, plugging it into the lighter socket, waiting until
it gets a reasonably stable lock (usually with an EPE of 7m), then I
manually calibrate the altimeter to 71m.

Driving to the start of my walk not only allows me to enjoy the
advantages of the road mapping whilst not consuming batteries, but also
gives the altimeter time for the auto-calibration to settle down, so
it's pretty stabilised by the time I start my walk.

Most impressively it's almost always within 1-2m of 71m when I return,
provided I keep the GPS switched on of course.

It's not accurate to less than a metre yet, but it's not far off. Just
wait until EGNOS gets activated! It probably won't improve accuracy at
home, but on a clear mountain top...

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

The message <[email hidden]>
from "Rodders" <[email hidden]> contains these words:

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard slog
for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Quoted message said:

Surely this cannot be right?

Troll alert.

The height of Ben Lomond can easily be established from a map and while
I was only 41 when I did that peak (my last Munro) I found it an easy
mornings stroll and nearly 20 years on still wouldn't consider such a
short walk hard.

FWIW the height of Ben Lomond was 3192 feet before it was metricated but
it is a moot point whether the height of 974m (3195.5 feet) is any more
accurate than the original height. Curiously the 974m height first
appeared on the First Series 1:50,000 which was supposedly just a
reworked 1". (The direct conversion is 973m).

--
Roger Chapman so far this year 64 summits
New - 42 (Marilyns 12, Sweats 5, Outlying Fells 30)
Repeats - 22( Marilyns 7, Sweats 16, Wainwrights 16)

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

Quoted message said:

The message <[email hidden]>
from "Rodders" <[email hidden]> contains these

words:

Quoted message said:

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard

slog

Quoted message said:

Quoted message said:

for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it

stated

Quoted message said:

Quoted message said:

3196ft but The Ben is 3300 ft.

Quoted message said:

Surely this cannot be right?

Troll alert.

The height of Ben Lomond can easily be established from a map and while
I was only 41 when I did that peak (my last Munro) I found it an easy
mornings stroll and nearly 20 years on still wouldn't consider such a
short walk hard.

Are you accusing me of being a Troll?

Rodders said:

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

Quoted message said:

The message <[email hidden]>
from "Rodders" <[email hidden]> contains these

words:

Quoted message said:

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard

slog

Quoted message said:

Quoted message said:

for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it

stated

Quoted message said:

Quoted message said:

3196ft but The Ben is 3300 ft.

Quoted message said:

Surely this cannot be right?

Troll alert.

Quoted message said:

Are you accusing me of being a Troll?

Well it did cross my mind too.

The subject of GPS accuracy is a subject we have had infinitum and
usually results in a long running argument involving the words map,
compass and GPS (yes I know those are initials) and navigating by bent
grass and the mossy sides of trees.

You haven't met Roger have you? He is the fastest walker posting on
this newsgroup, with the possible exception of David Laight. Ignore
all statements by him claiming to be unfit these days and not being
able to keep up. He'll walk any of us into the ground. Of course he
doesn't have umpteen cameras to carry like some of us. :-)
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Rodders <[email hidden]> wrote

Quoted message said:

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

Quoted message said:

The message <[email hidden]>
from "Rodders" <[email hidden]> contains these

words:

Quoted message said:

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard

slog

Quoted message said:

Quoted message said:

for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it

stated

Quoted message said:

Quoted message said:

3196ft but The Ben is 3300 ft.

Quoted message said:

Surely this cannot be right?

Troll alert.

The height of Ben Lomond can easily be established from a map and while
I was only 41 when I did that peak (my last Munro) I found it an easy
mornings stroll and nearly 20 years on still wouldn't consider such a
short walk hard.

Are you accusing me of being a Troll?

<Pants, recovering breath>

No - I just ran up Ben Thingummyjig after carefully calibrating my Etrex
Panorama, and I made it 3195 ft.

Gekos are rubbish.
--
Gordon

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

Quoted message said:

Rodders said:

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

Quoted message said:

The message <[email hidden]>
from "Rodders" <[email hidden]> contains these

words:

Quoted message said:

> Climbed Ben Lomond today, I don't care what anyone says, this is a

hard

Quoted message said:

Quoted message said:

slog

Quoted message said:

> for a 45yr old guy.
> Anyway, I took a reading at the top with my garmin Geko 201 and it

stated

Quoted message said:

> 3196ft but The Ben is 3300 ft.

> Surely this cannot be right?

Troll alert.

Quoted message said:

Are you accusing me of being a Troll?

Well it did cross my mind too.

Did you look at my second post which was within minutes of my first showing
two links? I have follwed Bens walks and have found them accurate and
enjoyable, obiously his height of Ben Lomond is way out, but it is there and
I thought, before further checking, that it was correct.

Rory

Rodders said:

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

Quoted message said:

Rodders said:

"Roger" <[email hidden]> wrote in message

Quoted message said:

Quoted message said:

Quoted message said:

> Troll alert.

Quoted message said:

Are you accusing me of being a Troll?

Well it did cross my mind too.

Did you look at my second post which was within minutes of my first showing
two links? I have follwed Bens walks and have found them accurate and
enjoyable, obiously his height of Ben Lomond is way out, but it is there and
I thought, before further checking, that it was correct.

Sorry, I haven't got a second post from you. Looking back now I have
about five posts by Rodders in the two months or so of postings I keep
and my newsfeed (freeserve.net) doesn't lose many posts. My original
reply (when the word troll popped into my mind) was within twenty
minutes of your original post.

So, this brings up another point. The accuracy of web-pages. I
wouldn't trust a walk or other information I got off a web-page
without checking it with a map or some other trusted reference. I
started off calculating the height of Ben Lomond in feet from the
figure in metres on the OS map (which I hapen to have available on my
PC) but then I checked it with a known source and my rough calculation
was out.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

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

Quoted message said:

Rodders said:

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

Quoted message said:

On Sat, 25 Sep 2004 11:13:06 +0100, Rodders wrote:

>"Roger" <[email hidden]> wrote in message

Quoted message said:

Quoted message said:

>> Troll alert.

>Are you accusing me of being a Troll?

Well it did cross my mind too.

Did you look at my second post which was within minutes of my first

showing

Quoted message said:

Quoted message said:

two links? I have follwed Bens walks and have found them accurate and
enjoyable, obiously his height of Ben Lomond is way out, but it is there

and

Quoted message said:

Quoted message said:

I thought, before further checking, that it was correct.

Sorry, I haven't got a second post from you. Looking back now I have
about five posts by Rodders in the two months or so of postings I keep
and my newsfeed (freeserve.net) doesn't lose many posts. My original
reply (when the word troll popped into my mind) was within twenty
minutes of your original post.

So, this brings up another point. The accuracy of web-pages. I
wouldn't trust a walk or other information I got off a web-page
without checking it with a map or some other trusted reference. I
started off calculating the height of Ben Lomond in feet from the
figure in metres on the OS map (which I hapen to have available on my
PC) but then I checked it with a known source and my rough calculation
was out.

Not a problem. This was the site I am referring to.

http://www.b-mercer.demon.co.uk/benl.htm

Rory

Rodders said:

This was the site I am referring to.

http://www.b-mercer.demon.co.uk/benl.htm

Rory

I wonder how old that page is?

Under maps required:

OS Landranger 56: Loch Lomond and Inveraray Area
OS Pathfinder NN 20/30: Arrochar and Ben Lomond
OS Pathfinder NS 29/39: Central Loch Lomond and Garelochhead
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Rodders said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard slog
for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Surely this cannot be right?

974m is a lot less than 3300' 3200' country... could be close.

Enjoy the views, was looking your way from Dumgoyne

Richard Webb

The altimetric accuracy of your GPS can depend on a couple of major factors;
some GPS's determine the altitude from the satellite signals and the
accuracy here depends on the signal strength. Other GPS's have a built in
barometric altimeter. I think the barometer ones are supposed to be more
accurate -assuming you set it to a known height recently.

I have a Garmin Etrex which has no barometer but the height readings
generally compare well to my Avocet wrist altimeter which is barometric.

Jay

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

Quoted message said:

Climbed Ben Lomond today, I don't care what anyone says, this is a hard

slog

Quoted message said:

for a 45yr old guy.
Anyway, I took a reading at the top with my garmin Geko 201 and it stated
3196ft but The Ben is 3300 ft.

Surely this cannot be right?

Rory

Jay said:

Other GPS's
have a built in barometric altimeter. I think the barometer ones are
supposed to be more accurate -assuming you set it to a known height
recently.

Just set it to auto-calibrate and it stays accurate.

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

Quoted message said:

Enjoy the views, was looking your way from Dumgoyne

Richard Webb

Thats what I am doing next. Did you park next to the war memorial as Ben
suggests in his site?

http://www.b-mercer.demon.co.uk/dum.htm

Rory

The message <[email hidden]>
from "Paul Saunders" <[email hidden]> contains these words:

Quoted message said:

Quoted message said:

Other GPS's
have a built in barometric altimeter. I think the barometer ones are
supposed to be more accurate -assuming you set it to a known height
recently.

Quoted message said:

Just set it to auto-calibrate and it stays accurate.

You hope.

On my last few visits to th ELD I have set the height correctly outside
my house before driving off but have still got discrepencies well in
excess of 100 feet for circular walks from the parked car. I can't
recall the exact figures and not being at home I can't access my records
but last Friday walk 1 had a start/finish height discrepancy of
approaching 200 feet and walk 2 (starting from just over a mile down the
road from the first) had one of over 100 feet. The GPS had been on
continuously (as had auto-cal).

--
Roger Chapman

roger said:

Quoted message said:

Just set it to auto-calibrate and it stays accurate.

You hope.

On my last few visits to th ELD I have set the height correctly
outside my house before driving off but have still got discrepencies
well in excess of 100 feet for circular walks from the parked car.

Really? I haven't used mine often enough to encounter such a variation.

Quoted message said:

I
can't recall the exact figures and not being at home I can't access
my records but last Friday walk 1 had a start/finish height
discrepancy of approaching 200 feet and walk 2 (starting from just
over a mile down the road from the first) had one of over 100 feet.
The GPS had been on continuously (as had auto-cal).

Did you calibrate the altimeter height *after* you got a decent lock?

Paul
--
http://www.wilderness-wales.co.uk
http://www.wildwales.fsnet.co.uk

Rodders said:

Quoted message said:

Enjoy the views, was looking your way from Dumgoyne

Richard Webb

Thats what I am doing next. Did you park next to the war memorial as Ben
suggests in his site?

http://www.b-mercer.demon.co.uk/dum.htm

I went up from the distillery. There has been a lot of erosion,
largely due to the summer storms this year, so go canny with the route
up the steep stuff, there is a lovely traverse ascent across the south
face which is very hill friendly and fun.

Watchout for the short grass, easy to slip and some bits of the hill
are exposed. Lovely place.

Richard Webb