Ski Speedometer
 

OK all, here is the challenge, come up with a viable way of measuring
your speed on skis.

I have heard tell of using GPS, but since it will only get your
horizontal speed component, and not the verticla, it will always read
low.

What else can you think of?

On 18 Jan 2006 02:51:50 -0800, "fat_boy" wrote:

OK all, here is the challenge, come up with a viable way of measuring
your speed on skis.

I have heard tell of using GPS, but since it will only get your
horizontal speed component, and not the verticla, it will always read
low.

Not so. They work in 3D so will be accurate on a slope too.

--
Ace (brucedotrogers a.t rochedotcom)
Ski Club of Great Britain - http://www.skiclub.co.uk
All opinions expressed are personal and in no way represent those of the Ski Club.

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.

I saw this on half baked, and it spiraled into a discussion on the
granularity of the surface of the piste.

What will really work though?

And not only that, because air is compressible its density with respect
to altitude is not constant, so the device would need calibrating (at
set altitude) to get an accurate change in altitude.

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

On Wed 18 Jan '06 at 10:51 "fat_boy" wrote:

OK all, here is the challenge, come up with a viable way of measuring
your speed on skis.

I have heard tell of using GPS, but since it will only get your
horizontal speed component, and not the verticla, it will always read
low.

What else can you think of?


Agree it does 3-d, but besides, your max speed will likely be on the
horizontal, i.e. when you bottom out of the run...

They claim to measure speed pretty well:

http://www.garmin.com/products/etrexVista/spec.html

Velocity: 0.05 meter/sec steady state

(that's about +/- 1.1mph)

Remember, it has the big error on your exact location, but velocity is
measured between two locations with the same error, thus that error is
removed.


My friend clocked 91.5mph last week. I'm not sure if that's good or not...



A.

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

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.

"fat_boy" wrote in message
oups.com...
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.


Considering the GPS system is primarily a military system used for aiming
missiles I think that the altitude is probably an important part of the
position!


--
Paul Schofield