GPS and Barometric pressure sensor recommendation please

"Sonoman" <billgates@microsoft.com> wrote in message
news:YuSdnbWB-aMUHZPcRVn-hw@comcast.com...
> Tauno Voipio wrote:
> > There is one more point to take into account, if the altitude is to
> > be measured with a pressure sensor: the reference pressure must
> > be set to match the current weather situation (called QNH or QFE).
> >
>
> So what you are telling me about the pressure is that I have to
> calibrate the barometric pressure sensor every time before I use it to
> take into account the weather changes? Interesting.
>
> I did not think that was necessary for my application. I want to know
> the altitude of each point in relation to each other and not against a
> reference (i.e. sea level), unless the weather changes in between
> readings I think I'll be ok without calibration, don't you think? I just
> don't want to complicate my life if I don't have to. Please advise.

Right.

A rule of thumb at low altitudes is 27 feet / millibar, or 8 meters /
hectopascal.

Tauno Voipio
tauno voipio (at) iki fi

On Tue, 03 Aug 2004 08:18:19 +0100, Paul Burke <paul@scazon.com>
wrote:

>Sacre Vert wrote:
>> 
>> I use a GPS unit that has a quoted accuracy of 4 metres for 50% of the
>> time.  This corresponds to the true position being within a ~50 square
>> metre area centred on the measurement result.  If you consider that
>> the surface area of the earth being some 510*10^12 square metres then
>> localising your position to 1 part in 10^13 is not bad.
>> 
>
>It is if you need to know whether you'll meet that 20m high cliff at the 
>bottom or the top, or where the corner of the house you are going to 
>build is NOW, after all, it will be there all the time, not just 50% of 
>the time, and 4m away could be on next door's land.
>
>Paul Burke
>
Also altitude is quoted on all GPS systems that I have ever seen, to
have a much greater margin of error than surface coordinates.

uguess@nowhere.net wrote in message news:<nf90h05ce5n7b17056gtehqgdg5c9eptgn@4ax.com>...
> On Tue, 03 Aug 2004 08:18:19 +0100, Paul Burke <paul@scazon.com>
> wrote:
> 
> >Sacre Vert wrote:
> >> 
> >> I use a GPS unit that has a quoted accuracy of 4 metres for 50% of the
> >> time.  This corresponds to the true position being within a ~50 square
> >> metre area centred on the measurement result.  If you consider that
> >> the surface area of the earth being some 510*10^12 square metres then
> >> localising your position to 1 part in 10^13 is not bad.
> >> 
> >
> >It is if you need to know whether you'll meet that 20m high cliff at the 
> >bottom or the top, or where the corner of the house you are going to 
> >build is NOW, after all, it will be there all the time, not just 50% of 
> >the time, and 4m away could be on next door's land.
> >
> >Paul Burke
> >
> Also altitude is quoted on all GPS systems that I have ever seen, to
> have a much greater margin of error than surface coordinates.

Altitude error will always be worse on a GPS system, at least until a
method is devised so that the receiver can see the satellites that are
below it. ;-)

1 part in 10^13 is pretty darn accurate.  IIRC when I was at college
the international definition of the second (the most accurately
defined standard unit) was accurate to 1 part in 10^12.  If you need
greater accuracy then you have to perform long term filtering of the
position data from a fixed installation, then you can get to the sub 1
metre fix.

S-V

Sonoman wrote:

> No, I was not aware. As far as I know it will give you longitude and 
> latitude which is like the X and Y axis. That sounds very interesting 
> and I will look into it. Thanks for the tip.

  Keep in mind most civilian GPS recievers will not resolve an altitude above 
60,000 feet.  Depending on what you're doing, this may or may not be a purchase 
consideration.

-- 
Linux Registered User # 302622                         <http://counter.li.org>

Sacre Vert wrote:
  > 1 part in 10^13 is pretty darn accurate.  IIRC when I was at college
> the international definition of the second (the most accurately
> defined standard unit) was accurate to 1 part in 10^12. 

That's like saying that fifty quid I owe you is peanuts compared with 
the size of the world economy, so I'll keep it.

Paul Burke

John Tserkezis wrote:
>  Keep in mind most civilian GPS recievers will not resolve an altitude 
> above 60,000 feet.  Depending on what you're doing, this may or may not 
> be a purchase consideration.

This is incorrect, the actual regulation prohibits exporting receivers 
capable of reporting position at greater than 60,000 feet *AND* 1000 
knots.  Some GPS manufacturers interpreted the AND as a logical OR in 
the past.  These days, most GPS chipsets will continue reporting 
position above 60,000 feet if speed is less than 1000 knots, and vice-versa.

Marc

Hi,
is anybody of you be able to decode rs80 signal??
I have tried with the "famous" german sheets intructions but i don not
understand how to use the calibration coefficients.

For example if these are the frequencies:

F1 = 9690 Hz for the first coefficient
F2 = 7665 Hz for the second coefficient
FT = 8876 Hz for the temperature sensor


Which is the temperature? if you try to calculate let me know!!

thank you for help.

enrico

In message <a9cf47b6.0408281229.fc3bf4b@posting.google.com>, BRUNCUSPINA 
<prohu@libero.it> writes
>Hi,
>is anybody of you be able to decode rs80 signal??
Vaisala RS80?
>I have tried with the "famous" german sheets intructions
Which 'Famous' German sheets?
>but i don not
>understand how to use the calibration coefficients.
>
>For example if these are the frequencies:
>
>F1 = 9690 Hz for the first coefficient
>F2 = 7665 Hz for the second coefficient
>FT = 8876 Hz for the temperature sensor
>
>
>Which is the temperature? if you try to calculate let me know!!
>
>thank you for help.
>
>enrico
Would love a link to the 'German Sheets'
-- 
Clint Sharp

On Tue, 31 Aug 2004 17:42:41 +0100, Clint Sharp 
<clint@clintsmc.demon.co.uk> wrote:

>> I have tried with the "famous" german sheets intructions
> Which 'Famous' German sheets?

I suspect this one: http://www.zfx.de/sonde/

   Vadim

Vadim Borshchev <vadim.borshchev@127.0.0.1> wrote in message news:<opsdm7qnu1y1ubid@news>...
> On Tue, 31 Aug 2004 17:42:41 +0100, Clint Sharp 
> <clint@clintsmc.demon.co.uk> wrote:
> 
> >> I have tried with the "famous" german sheets intructions
> > Which 'Famous' German sheets?
> 
> I suspect this one: http://www.zfx.de/sonde/
> 
>    Vadim


The old link is disappeared but fortunately I had saved the pdf file
so now look at http://prohu.altervista.org/convert.pdf

Let me know.

greetings

enrico