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  #21  
Old January 18th 06, 05:39 PM
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In message .com
"fat_boy" wrote:

How? If a GPS devices prime role is to give the lat and long, it will
give you your position in terms of a flat grid on the earths surface.

For it to calculate speed, it measures the change in distance over time
relative to that flat grid.

So, unless the GPS unit ALSO measures altitude, and can add a vertical
component to the calculation, it can not work for skiing.


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.

I've collected active data on the Geko 301 whilst skiing and it is easy
to analyse data later on a PC for all kinds of parameters using software
such as GPS Utility.

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"
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  #22  
Old January 18th 06, 05:48 PM
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Ian Blake NoNotMe@NotAnywhere wrote:

On Wed, 18 Jan 2006 14:33:17 +0100, davidof
wrote:

fat_boy wrote:
How? If a GPS devices prime role is to give the lat and long, it will
give you your position in terms of a flat grid on the earths surface.

For it to calculate speed, it measures the change in distance over time
relative to that flat grid.

So, unless the GPS unit ALSO measures altitude


they do


And devices such as the Garmin Geko 300 also contain an altimeter to
assist the accuracy problems with altitude detection. Also very
portable. I am not sure how it would stand up to the cold. The
batteries will certainly be rubbish in such temperatures.


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.

When ski-touring I tend not to have the device on all day but only
intermittently to record major waypoints and features along the route. I
also carry alkaline or lithium AAA instead of the NiMh cells. Under such
circumstances I've usually found two sets of batteries enough for at
least a weeks worth of touring data with capacity to spare in case I
need to use the device for emergency navigation.

Mike http://www.path.cam.ac.uk/~mrc7/hauteroute/
--
o/ \\ // |\ ,_ o Mike Clark
\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
" || _`\,_ |__\ \ | immunology lecturer, antibody engineer and
` || (_)/ (_) | \corn computer user"
  #23  
Old January 18th 06, 08:08 PM
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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

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Adrian Shaw ais@
Adran Cyfrifiadureg, Prifysgol Cymru, aber.
Aberystwyth, Ceredigion, Cymru ac.
http://users.aber.ac.uk/ais uk
  #24  
Old January 18th 06, 08:54 PM
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On 18 Jan 2006 04:53:32 -0800, "fat_boy" wrote:

How? If a GPS devices prime role is to give the lat and long, it will
give you your position in terms of a flat grid on the earths surface.

For it to calculate speed, it measures the change in distance over time
relative to that flat grid.

So, unless the GPS unit ALSO measures altitude, and can add a vertical
component to the calculation, it can not work for skiing.


Do you get off on displaying your ignorance to the world?
--
Champ
  #26  
Old January 18th 06, 11:14 PM
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What's the point? 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



  #27  
Old January 18th 06, 11:14 PM
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Alun Evans wrote:


On Wed 18 Jan '06 at 13:51 "fat_boy" wrote:

91? Thats extraordinary. Does he often get that speed with GPS or is
it a freak result?



nah, that was peak, and a schuss down a pisted black.


Though we'd regularly hit around 50mph carving reds / blacks.

You can test the GPS in the car, it's quite accurate.


Actually, what was a good test was that it would hit chair lift speeds dead
on, and they do change altitude significantly.




A.


For a while I carried a GPS (an etrek) around with me and recorded the
fastest speed of the day and the distance traveled (more interesting
since the maximum speed was around the same every day). Every so often
we would get a freak reading on maximum speed which I put down to
inaccuarices between two consequative readings and a subsequent jump in
speed. Since these often occurred on steep terrain my guess was that
they were either to do with the vertical measurement and that the GPS
calculated actual speed not just the horizontal component, or
alternatively due to multi pathing where the GPS signal is reflected
before reaching the receiver.

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

John
  #29  
Old January 19th 06, 08:31 AM
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fat_boy wrote:
davidof above rekoned all GPSs look at altitude too. But I gues not.


Here is a body that might interest you:-

http://en.wikipedia.org/wiki/Flat_Earth_Society
  #30  
Old January 19th 06, 10:31 AM
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"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


 




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