Ski Speedometer

"John Elgy" wrote in message
...

Basically you can trust the average speeds given by the GPS but don't bet
your life savings on a single 'maximum speed' recording.

Its important to understand that GPS receivers calculate speed by taking
sample positions every few seconds, then working out how fast you would have
to be travelling to get from point to point. There are smoothing algorithms
involved but they are not perfect.

There's an effect called multipath which can make nonsense of small samples.
It tends to show up in areas with lots of tall buildings, and unfortunately
for our purposes, in mountainous terrain. If you suddenly lose direct sight
of a satellite, but you can still receive the signal as it bounces off the
other side of the canyon, the GPS is fooled into thinking that you are now
twice the width of the canyon away from the last sample point, and so it
calculates your speed accordingly. This is a crude over-simplification but
the effect does happen. It also depends on the current positions of the
satellites, so it won't always happen in the same place every time. I had
first-hand experience of this last week as, [returning to the topic of
skiing], my GPS recorded me zig-zagging wildly (+/- 500 feet either side) up
a chairlift in La Rosiere. Yes, it was windy, but not that windy ;-)

Walter

In message
"Walter Wright" wrote:


"Mike Clark" wrote in message
.uk...

No problem with the batteries. Skiing on piste last week in Les Arc I
was using my Geko301 with 800mAh NiMh rechargeables. I had the device
attached to my rucksack shoulder strap. Temperatures were about -4 to
-10 during the week. One set of fully charged batteries would just about
last from 9.30am until 4.30pm. In practice I took two sets of batteries
out each day and changed them over mid-day and then recharged all four
each evening.

You might find the batteries last longer if you keep them warm. I use
a Garmin eMap with 2x1800mAh NiMh. I keep the eMap in an inside
jacket pocket and use an external antenna (just a bit of wire to a 1"
GPS mouse velcro'd to my collar). A set of batteries lasts about 2 -
2.5 days between charges.

Walter



You are right that keeping the batteries warmer will mean they last
longer but for days spent skiing on piste, or even for day walks it is
an equally pragmatic solution to carry an extra set of AAA rechargeable
cells and then to change them over in the middle of the day. If you have
access to a charger in the evenings, especially one that is computer
controlled and monitors the levels of individual cells, it makes little
difference if you charge them for a shorter period every evening, or a
longer period every few days.

On the other hand when I am out on multi-day tours I tend to use Lithium
cells and to keep the unit in an inside pocket and use it intermittently
for recording relenant way points along the route.

Mike http://www.path.cam.ac.uk/~mrc7/cccc/hauteroute/
--
o/ \\ // |\ ,_ o Mike Clark
\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
" || _`\,_ |__\ \ | immunology lecturer, antibody engineer and
` || (_)/ (_) | \corn computer user"

"Mike Clark" wrote in message
.uk...
or even for day walks it is
an equally pragmatic solution to carry an extra set of AAA rechargeable
cells and then to change them over in the middle of the day.

I'd forgotten that the Gekos use AAA cells as opposed to AA. That must limit
your mAhs significantly.

Walter

Angus Gilmour wrote:

What's the point?

Indeed, what is the point of skiing?

Every one skis for different reasons - some to race, some to go fast,
some to find excitement and some to challenge themselfs and learn new
skills. Some, indeed, prefer posing and some, if you believe the Sunday
Newspapers, go purely to go to lunch. You pays your money and you takes
your choice. It is up to you.

Isn't it better to get down the slopes in style rather
than seeking to get an extra turn of speed fom the waxes that are applied?

You could always have a word with a copper and see if you can borrow a speed
gun, if you feel that the bald measurement of speeed will define your
prowess as a skier.



"Adrian D. Shaw" wrote in message
...

Felly sgrifennodd Alun Evans :

Velocity: 0.05 meter/sec steady state

(that's about +/- 1.1mph)

You mean +/- 0.11 mph I think. Try google "0.05 m/s in mph".

Adrian

--
Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk

You're clearly out of touch with modern GPS devices. I have a Geko301
which includes data for both barometric and GPS altimeter and can do
auto correction of one by the other over time. The software in the
device also includes algorithms to calculate things such as glide ratio,
average rate of descent and also average rate of ascent, primarily
designed for aerial pursuits such as parachuting and paragliding but it
would also allow the read out of a ski descent.

So some can and some cant. We have already discovered that.

I like going quick. And this question arose about exactly how fast one
does ski, and is it close to our guesses.

There is no need to turn this discussion into something it isnt.

They were using TERCOM not GPS

Do you get off on displaying your ignorance to the world?
=20
You f=FCcking prick.

fat_boy wrote:
Do you get off on displaying your ignorance to the world?


You fücking prick.

Ah, so you CAN quote context when it suits you ?

CANT.

In message
"Walter Wright" wrote:


"Mike Clark" wrote in message
.uk...
or even for day walks it is
an equally pragmatic solution to carry an extra set of AAA rechargeable
cells and then to change them over in the middle of the day.

I'd forgotten that the Gekos use AAA cells as opposed to AA. That must
limit your mAhs significantly.

Walter


In warm weather a pair of 800mAh AAA NiMh cells gives more than 8 hours
of continuous use. Before I changed to a Geko301 I used to use an Etrex
Summit which uses AA cells. The Geko plus two sets of cells is smaller
and lighter than the Etrex with one set of cells.

For ski-touring I'm happy with the weight and size saving with the Geko
and don't find the AAA cells any disadvantage in use.

Mike http://www.path.cam.ac.uk/~mrc7/cccc/hauteroute/
--
o/ \\ // |\ ,_ o Mike Clark
\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
" || _`\,_ |__\ \ | immunology lecturer, antibody engineer and
` || (_)/ (_) | \corn computer user"