GPS possition was several nm vrong
 

The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until 3
hours later. Then the satellite were labelled "unhealthy" so it would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

Possition is wrong, and so is vrong.

Why doesn't my spellchecker check the subject line ?

Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

So you mean Bobsprit could be sailing in what he thinks is LIS and actually
be in Toledo? Kewl!

M.

Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

I think the actual position fault was less than that, but in Bobsprits
case - who knows ?

Peter S/Y Anicula

"Michael" skrev i en meddelelse
...
So you mean Bobsprit could be sailing in what he thinks is LIS and
actually
be in Toledo? Kewl!

M.

Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a
distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately,
and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station
until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to
several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful
and
cheap device.


Peter S/Y Anicula

No wonder Jax can't find the Gulf Stream!

Ole Thom

Funny you should mention Toledo, sailing on Lake Erie last week in the
vicinity of several power plants I noticed my gps acting up, wondering if
they have the ability to mess with the signal in certain areas? Or maybe
it's just my ageing free Cadillac gps?
John Cairns
----- Original Message -----
From: "Michael"
Newsgroups: alt.sailing.asa
Sent: Sunday, August 15, 2004 2:10 PM
Subject: GPS possition was several nm vrong


So you mean Bobsprit could be sailing in what he thinks is LIS and
actually
be in Toledo? Kewl!

M.

Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

"John Cairns" wrote in message
m...
Funny you should mention Toledo, sailing on Lake Erie last week in
the
vicinity of several power plants I noticed my gps acting up,
wondering if
they have the ability to mess with the signal in certain areas? Or
maybe
it's just my ageing free Cadillac gps?

Mine still works fine, though I barely use it.

Scotty

"Michael" wrote in message ...
So you mean Bobsprit could be sailing in what he thinks is LIS and actually
be in Toledo? Kewl!

M.


Hey Michael,

Saw the ship you were talking about named after my sailboat!
Thats one big MF. Fairly new as well. Looks like it could carry a
whole bunch of stuff

Joe



Peter S/Y Anicula


"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

You are never VRONG!

I just found out that there are english versions of the pages I linked
to:

http://www.frv.dk/en/nyheder/nyheder.htm#54
http://www.frv.dk/en/ifm/navigation/gps.htm

"Peter S/Y Anicula" skrev i en
meddelelse ...
The 1. jan 2004 around 18.30 UTC, the clock in one of the
GPS-satellites had a malfunction. This resulted in a distance-fault
from this satellite of up to 285 km (normally under 10 meter).

A fault like that is not serious if it is spotted immediately, and
the
satellite is put out of play, so it isn't used in the position
calculation.
In this case the fault wasn't spotted by the GPS-earth-station until
3
hours later. Then the satellite were labelled "unhealthy" so it
would
be left out of the calculations.

For 3 hours GPS receivers calculated faulty positions up to several
nm
out of place.

Published 30. jun 2004: http://www.frv.dk/ifm/navigation/gps.htm
This link is better: http://www.frv.dk/nyheder/nyheder.htm#54

This illustrates the limitations of this in many ways wonderful and
cheap device.


Peter S/Y Anicula

Peter S/Y Anicula wrote:
I just found out that there are english versions of the pages I linked
to:

http://www.frv.dk/en/nyheder/nyheder.htm#54
http://www.frv.dk/en/ifm/navigation/gps.htm

Thanks for the info & the links, Peter.

I'm not sure I understand this- you can tell your GPS to ignore or put
less priority on certain satellites? That would be a very cool feature.

It's amazing how many people have no idea how to navigate without GPS...
a lot of people who use to know are so out of practice that they are
functionally lost without it.

On our last trip, a relatively short river jaunt of a few days (rudely
interrupted by H. Bonnie and H. Charley), we were rather sloppy for the
first day and had a lot of household junk piled on the chart table. When
I realized I couldn't lay out a course, I threw it all on the floor (I
was in a hurry, I cleaned it up myself later). We had a "serious" talk
about the unwisdom of sloppy practices... the arriving hurricanes later
in the week emphasized this!

Fresh Breezes- Doug King

Doug Wrote:

I'm not sure I understand this- you can tell your GPS to ignore or
put
less priority on certain satellites? That would be a very cool
feature.


I don't know. First I thought it was a build in feature in all GPS
receivers, that they ignored satellites marked "unhealthy".

As I read the later parts of the article I got confused:

"...some users believe that the DGPS system is not necessary anymore.
However, this is not correct as the great advantage of the DGPS system
is the ability to warn the users in case of faults on the GPS/DGPS
system, by an "Integrity Warning". "

".... by using the DGPS system the users, as earlier mentioned, are
warned about faults in the system, as a "station unhealthy" alarm from
the Integrity Monitor is generated."

Does this mean that most of the GPS receivers that sailors use do not
have these facilities, and do not detect the "unhealthy" label ?

Would be interesting to find out. (One day, when I have the time...)


It's amazing how many people have no idea how to navigate without
GPS...
a lot of people who use to know are so out of practice that they are
functionally lost without it.

...we were rather sloppy for the first day...

Yes, when it (GPS) works so well most of the time, it is so easy to
get lazy. I know that from experience.

The following statement seems clear enough though:
"The circumstances of this satellite fault shows that it can not be
emphasized enough, that the GPS and DGPS users at all times should be
aware of the fact that the systems can fail. They should therefore not
blindly trust the electronic aids, but use all available aids to
navigation as radar, buoys and beacons and so on when navigating in
difficult waters."

Peter S/Y Anicula






"DSK" skrev i en meddelelse
...
Peter S/Y Anicula wrote:
I just found out that there are english versions of the pages I
linked
to:

http://www.frv.dk/en/nyheder/nyheder.htm#54
http://www.frv.dk/en/ifm/navigation/gps.htm

Thanks for the info & the links, Peter.

I'm not sure I understand this- you can tell your GPS to ignore or
put
less priority on certain satellites? That would be a very cool
feature.

It's amazing how many people have no idea how to navigate without
GPS...
a lot of people who use to know are so out of practice that they are
functionally lost without it.

On our last trip, a relatively short river jaunt of a few days
(rudely
interrupted by H. Bonnie and H. Charley), we were rather sloppy for
the
first day and had a lot of household junk piled on the chart table.
When
I realized I couldn't lay out a course, I threw it all on the floor
(I
was in a hurry, I cleaned it up myself later). We had a "serious"
talk
about the unwisdom of sloppy practices... the arriving hurricanes
later
in the week emphasized this!

Fresh Breezes- Doug King