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'[OT]: GPS for Speed, was:Wind Speed Formula'
2001\02\12@161338 by Barry King

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> GPS won't do you much good if there's wind as you're driving.  You'll need
> to do two (or more) passes in different directions to cancel out the effect
> of wind.

Hmm.  Does a GPS really give you an instantaneous ground speed
reading that is accurate and updated often (like 1 Hz?)  The only one
I've played with gives erratic speeds, they seem to be long-term
averages, so if you are speeding up and slowing down, they aren't
accurate.  And they are not updated very often.  This was at approx
25 mph (marine application), with I think 5 satelites in view.  Is
the erratic data because it was a stupid receiver, or it that a
limitation of the tech?

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2001\02\12@175454 by goflo

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> Hmm.  Does a GPS really give you an instantaneous ground speed
> reading that is accurate and updated often (like 1 Hz?)  The only one
> I've played with gives erratic speeds, they seem to be long-term
> averages, so if you are speeding up and slowing down, they aren't
> accurate.  And they are not updated very often.  This was at approx
> 25 mph (marine application), with I think 5 satelites in view.  Is
> the erratic data because it was a stupid receiver, or it that a
> limitation of the tech?

FWIW, with a Magellan Blazer12 - Speed seems somewhat erratic
walking around -  bicycling, driving, or flying, it seems to
track perfectly.

Jack

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2001\02\12@221230 by Roman Black

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Barry King wrote:

> Hmm.  Does a GPS really give you an instantaneous ground speed
> reading that is accurate and updated often (like 1 Hz?)  The only one
> I've played with gives erratic speeds, they seem to be long-term
> averages, so if you are speeding up and slowing down, they aren't
> accurate.  And they are not updated very often.  This was at approx
> 25 mph (marine application), with I think 5 satelites in view.  Is
> the erratic data because it was a stupid receiver, or it that a
> limitation of the tech?


No generally GPS won't give a good instantaneous road
speed. Many customers who buy our speedo recalibrator
product try to use a GPS to calibrate it, but you really
need a long distance and cosntant speed for the GPS to
give a decent average speed reading.

For the wind meter caibration, you can get decent
"hobby" wind speed meters from RadioShack, etc,
maybe if someone is serious about building weather
measuring equipment the $50 would be well spent?
I have one. :o)
-Roman

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2001\02\12@221850 by David VanHorn

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>
>For the wind meter caibration, you can get decent
>"hobby" wind speed meters from RadioShack, etc,
>maybe if someone is serious about building weather
>measuring equipment the $50 would be well spent?
>I have one. :o)
>-Roman


Do you find the Kestrel products accurate?

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2001\02\12@232123 by Roman Black

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David VanHorn wrote:
>
> >
> >For the wind meter caibration, you can get decent
> >"hobby" wind speed meters from RadioShack, etc,
> >maybe if someone is serious about building weather
> >measuring equipment the $50 would be well spent?
> >I have one. :o)
> >-Roman
>
> Do you find the Kestrel products accurate?


I'm in Australia, I don't know what a Kestrel is!
My wind meter is a Dick Smith one, (another hobby
store) and it is pretty good. I don't buy from
Radio Shack, they are very dear here in Aust.
I used Radio Shack as an example hobby store,
sorry if their particular wind meter is no
good.:o)
-Roman

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2001\02\12@234029 by David VanHorn

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>
> > Do you find the Kestrel products accurate?
>
>
>I'm in Australia, I don't know what a Kestrel is!

It's a sort of bird, or a moderately expensive hand-held weather station.
The EOC set us up with Kestrel 3000's which have current, peak, average,
gust, plus temp, humidity, dew point, etc.


>I used Radio Shack as an example hobby store,
>sorry if their particular wind meter is no
>good.:o)

Hmm.. Never seen one here.
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2001\02\13@032502 by Chris Carr

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> Barry King wrote:
>
> > Hmm.  Does a GPS really give you an instantaneous ground speed
> > reading that is accurate and updated often (like 1 Hz?)  The only one
> > I've played with gives erratic speeds, they seem to be long-term
> > averages, so if you are speeding up and slowing down, they aren't
> > accurate.  And they are not updated very often.  This was at approx
> > 25 mph (marine application), with I think 5 satelites in view.  Is
> > the erratic data because it was a stupid receiver, or it that a
> > limitation of the tech?
>
Roman Black Wrote
>
> No generally GPS won't give a good instantaneous road
> speed. Many customers who buy our speedo recalibrator
> product try to use a GPS to calibrate it, but you really
> need a long distance and cosntant speed for the GPS to
> give a decent average speed reading.

Hence the reason for using an Airfield Runway as well as the fact they are
well away from buildings and other structures. They are stright and flat, at
least all the ones within a 30 mile radius of me are (I'm talking proper
paved runways not the grass ones). With a bit of practice it is relatively
easy to keep a vehicle at a speed constant enough to calibrate a wind speed
indicator.

From experience, it's the cheapest and quickest way of getting fairly
accurate results, assuming  you have access to a GPS Receiver. If you
haven't then it's wood or metal work and a bicycle wheel (plus a PIC).
>
> For the wind meter caibration, you can get decent
> "hobby" wind speed meters from RadioShack, etc,
> maybe if someone is serious about building weather
> measuring equipment the $50 would be well spent?
> I have one. :o)

Suck Index Finger and stick it up in the Air. No that's for the accurate
measurement of wind direction Sorry. :-)

Chris

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