Mike Causer wrote:
On Thu, 05 Jan 2006 22:14:22 +0000, PetDragon wrote:

I'm just interested in finding out that's all.

http://www.ordnancesurvey.co.uk/oswebsite/getamap/

Or on handy, portable, paper at many bookshops.



Mike

Well said. I have over a hundred at home. It's perfectly
possible to trace contours in built-up areas on an OS 1:25000 map.
With the vertical interval of 5 m combined with local knowledge you can
determine your height to the nearest metre quite easily. My brother's
GPS contraption was out by about 5 metres. I was far too polite to
denigrate his expensive toy. The daft thing is, he can read maps very
well. *rolls eyes upwards*.

Tudor Hughes, Warlingham, Surrey. Alt. 169 m give or take a foot.

On 6 Jan 2006 05:47:35 -0800, "Tudor Hughes" wrote:

My brother's
GPS contraption was out by about 5 metres.

The GPS system wasn't designed to provide an accurate altitude.
Altitude errors can be one-and-a-half to twice the horizontal error.
The altitude that's displayed is the distance from the centre of the
earth less the distance from the centre of the earth of the local
geoid. The local geoid is stored in the receiver and may not be
particularly accurate.

E&OE

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Loch Goil and Loch Long in Argyll, Scotland.
Web cam and weather:- http://www.windycroft.gt-britain.co....her/kabcam.htm
Some walks and treks:- http://www.windycroft.gt-britain.co.uk/walks/

PetDragon wrote:
I'm just interested in finding out that's all.

Use an altimeter.
Get current air pressure in your area from:
http://www.bbc.co.uk/weather/ukweather/pressure.shtml

Set zero on altimeter to pressure and the needle with give your height.
Cheers

Jonathan Stott wrote:

John_H wrote:

Differential GPS is very accurate.

Ordinary hand held GPS isn't too bad if the satellites are in the
right position -- mine usually gets within a metre a so whenever it
gives a steady altitude reading (if the reading drifts it won't be
accurate).

Ordinary GPS can be significantly out! The first thing I did when I got
my device was to take my height - it reckoned (after letting it settle
for a while) that I was at -14m. While that's only 22m out, it's still
quite inaccurate!

It certainly can be a long way out, and will be if the reading has any
tendency to drift over a time period (say five minutes). Allowing
time to 'settle down' won't achieve accuracy -- you must get a
consistent identical reading over time. It may take several attempts
at different times of the day to find the favourable satellite
distribution needed.

I do have the advantage of having set up (and rechecked) my weather
station with DPGS so I know its altitude exactly. I've also taken
numerous readings against it with various handhelds, which have
cosistently confirmed the above.

--
John H