gps sattelites...

[Hul Tytus]

Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

Hul

 

[Martin Brown]

On 11/06/2022 09:02, Hul Tytus wrote:

Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

http://heavens-above.com/

Will predict positions of most satellites bright enough to see with the
naked eye (or which flare bright enough to see sometimes).

Feeding in the orbital elements of the GPS satellites or knowing their
names should get you predictions of visibility for lat, long & time.

One I have never used seems to have their orbital elements in its database:

https://in-the-sky.org/spacecraft_elements.php?id=41328

Quite a lot of work to do it manually so you are probably going to need
to write a program taking as input their latest orbital elements and
then looking for the times when N or more GPS satellites are visible to you.

--
Regards,
Martin Brown

 

[Gerhard Hoffmann]

Am 11.06.22 um 10:02 schrieb Hul Tytus:

Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

The GPS system sends the data of all sats. The receivers need to know
that. Probably you can ask your receiver.

Try Lady Heather\'S Disciplined Oscillator control program
< http://www.ke5fx.com/heather/readme.htm >

Gerhard

 

[Ricky]

On Saturday, June 11, 2022 at 4:02:32 AM UTC-4, Hul Tytus wrote:

Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

Are you taking readings over a wide area? The constellation doesn\'t vary with location until you move significant distances... unless you are dealing with significant variations in horizons. I don\'t think horizon effects are going to be included in any databases.

You will get your best readings from sats spread around the sky. So including sats near the horizon would be important to minimize the calculation errors.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[John Miles, KE5FX]

On Saturday, June 11, 2022 at 5:45:00 AM UTC-7, Ricky wrote:

You will get your best readings from sats spread around the sky. So
including sats near the horizon would be important to minimize the
calculation errors.

Only to some extent. While you want a good spread, you actually want to
exclude SVs that are very close to the horizon because they\'re the ones
most vulnerable to multipath and propagation disturbances. Many receivers,
including all timing-grade receivers, use an elevation mask to avoid that.

For the same reason, the better antennas tend to use choke rings or other
ground topologies to discourage low-angle reception.

-- john, KE5FX

 

[Hul Tytus]

Martin - thanks for the info, especially the \"spacecraft elements\" at in-the-sky.org. From
what\'s there, I need to learn the meaning of the terms shown and the procedure
for predicting positions at a given time. Any suggestions?

Hul

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 11/06/2022 09:02, Hul Tytus wrote:
Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

http://heavens-above.com/

Will predict positions of most satellites bright enough to see with the
naked eye (or which flare bright enough to see sometimes).

Feeding in the orbital elements of the GPS satellites or knowing their
names should get you predictions of visibility for lat, long & time.

One I have never used seems to have their orbital elements in its database:

https://in-the-sky.org/spacecraft_elements.php?id=41328

Quite a lot of work to do it manually so you are probably going to need
to write a program taking as input their latest orbital elements and
then looking for the times when N or more GPS satellites are visible to you.

--
Regards,
Martin Brown

 

[Hul Tytus]

Gerhard I looked at \"heather\" and I\'ll keep a record of same. Currently
I\'m too much of a rube in sattelite language and information to be able
to pick needed data from the mass available there.

Hul


Gerhard Hoffmann <dk4xp@arcor.de> wrote:

Am 11.06.22 um 10:02 schrieb Hul Tytus:
Anyone know where a schedule of the times of orbit of the GPS sattelites
might be found? Given such data, forecasting a good time for taking readings
at a specific location should be possible. Eliminating multiple readings over
several days would be the enjoyable result.

The GPS system sends the data of all sats. The receivers need to know
that. Probably you can ask your receiver.

Try Lady Heather\'S Disciplined Oscillator control program
http://www.ke5fx.com/heather/readme.htm

Gerhard

 

[Hul Tytus]

John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.

Hul

John Miles, KE5FX <jmiles@gmail.com> wrote:

On Saturday, June 11, 2022 at 5:45:00 AM UTC-7, Ricky wrote:
You will get your best readings from sats spread around the sky. So
including sats near the horizon would be important to minimize the
calculation errors.

Only to some extent. While you want a good spread, you actually want to
exclude SVs that are very close to the horizon because they\'re the ones
most vulnerable to multipath and propagation disturbances. Many receivers,
including all timing-grade receivers, use an elevation mask to avoid that.

For the same reason, the better antennas tend to use choke rings or other
ground topologies to discourage low-angle reception.

-- john, KE5FX

 

[Martin Brown]

On 12/06/2022 00:53, Hul Tytus wrote:

Martin - thanks for the info, especially the \"spacecraft elements\" at in-the-sky.org. From
what\'s there, I need to learn the meaning of the terms shown and the procedure
for predicting positions at a given time. Any suggestions?

The bible for that sort of thing is Jean Meeus\'s book Astronomical
Algorithms but it is nearly out of print and copies in the USA sell for
insane prices. These guys still have reasonably priced stock.

https://www.firstlightoptics.com/books/astronomical-algorithms.html

(chapters 29 through 33 - assumes moderately advanced maths)

Bad news is it doesn\'t deal with terrestrial satellites only solar
system objects but the principles are the same it is just that there are
drag and oblateness corrections for orbiting the Earth in addition.

And also a much more significant correction for the observer being sat
on the surface of the Earth rather than at its centre. Objects in near
Earth orbit are subject to a lot of parallax from the ground.

Offhand I don\'t know of any code that does it very accurately (like the
GPS code does) but then you may not need great accuracy provided the
satellite positions are indicative of how many you have in the sky at
any one time. Never used any of these but worth a look:

https://listoffreeware.com/satellite-tracking-software-windows/

https://www.satsignal.eu/software/wxtrack.htm

Hope this is some help.

Regards,
Martin Brown

 

[Hul Tytus]

I\'m using the NMEA sentences from the reciever. That allows shifting
from, in my case, Ublox to Skytrack receivers, with minimal effort.
The \"terminal\" I\'ve setup collects satelitte names & info which ...
hmmm... that includes the position of the satellites which should be
useful, could even generate the ability to predict positions from a heap
of past data. Should be something simpler though.
I\'ll take a look qsl.net.

Hul

rbowman <bowman@montana.com> wrote:

On 06/11/2022 06:15 PM, Hul Tytus wrote:
John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.

Are you getting NMEA sentences from the receiver?

http://www.satsleuth.com/GPS_NMEA_sentences.aspx

I discard everything other the GPRMC since I\'m tracking mobile units but
GPGSV gives the information on the satellites in view. Not useful for
prediction but it might be of interest.

If you\'re on Linux:

https://www.qsl.net/kd2bd/predict.html

 

[Hul Tytus]

Martin - thanks for the suggestion. I\'ll give Meeus\' book a try. Accuracy of
the orbital need not be great for this application, as you mention.
I looked at Meeus\' book once when seeking a procedure for calculating the
sun\'s position and was supprised at the lack of accurracy. Someone\'s keeping
their methods close to the vest.

Hul

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 12/06/2022 00:53, Hul Tytus wrote:
Martin - thanks for the info, especially the \"spacecraft elements\" at in-the-sky.org. From
what\'s there, I need to learn the meaning of the terms shown and the procedure
for predicting positions at a given time. Any suggestions?

The bible for that sort of thing is Jean Meeus\'s book Astronomical
Algorithms but it is nearly out of print and copies in the USA sell for
insane prices. These guys still have reasonably priced stock.

https://www.firstlightoptics.com/books/astronomical-algorithms.html

(chapters 29 through 33 - assumes moderately advanced maths)

Bad news is it doesn\'t deal with terrestrial satellites only solar
system objects but the principles are the same it is just that there are
drag and oblateness corrections for orbiting the Earth in addition.

And also a much more significant correction for the observer being sat
on the surface of the Earth rather than at its centre. Objects in near
Earth orbit are subject to a lot of parallax from the ground.

Offhand I don\'t know of any code that does it very accurately (like the
GPS code does) but then you may not need great accuracy provided the
satellite positions are indicative of how many you have in the sky at
any one time. Never used any of these but worth a look:

https://listoffreeware.com/satellite-tracking-software-windows/

https://www.satsignal.eu/software/wxtrack.htm

Hope this is some help.

Regards,
Martin Brown

 

[Martin Brown]

On 12/06/2022 11:46, Hul Tytus wrote:

Martin - thanks for the suggestion. I\'ll give Meeus\' book a try. Accuracy of
the orbital need not be great for this application, as you mention.
I looked at Meeus\' book once when seeking a procedure for calculating the
sun\'s position and was supprised at the lack of accurracy. Someone\'s keeping
their methods close to the vest.

The full methods for the solar system are published as VSOP82 onwards.
Current one is VSOP2013. It is a semianalytic fit to numerical
integration and incredibly accurate.

Observations of a pulsar that got really close to Jupiter found a
problem with the FORTRAN continuation cards (>10) generated by the
symbolic algebra program. For a moment it looked like relativity was not
predicting the right time delay for light passing close to Jupiter. But
it turned out that Jupiter wasn\'t where the theory said it was.

Fixed from VSOP87 onwards. That is good enough for most purposes...

Almost all planetarium programs use this VSOP method now.

https://en.wikipedia.org/wiki/VSOP_model

--
Regards,
Martin Brown

 

[Martin Brown]

On 12/06/2022 01:15, Hul Tytus wrote:

John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.

If you don\'t mind getting a biassed estimate then the minimum variance
estimate will weight down any sporadic glitches automatically.

Likewise for minimum 1-norm estimates (ie median rather than mean).

Unweighted least squares pays too much attention to the outliers.
(and the thing that is certain is that will have the odd one)


--
Regards,
Martin Brown

 

[Clifford Heath]

On 12/6/22 18:00, Martin Brown wrote:

On 12/06/2022 00:53, Hul Tytus wrote:
Martin - thanks for the info, especially the \"spacecraft elements\" at
in-the-sky.org. From
what\'s there, I need to learn the meaning of the terms shown and the
procedure
for predicting positions at a given time. Any suggestions?

The bible for that sort of thing is Jean Meeus\'s book Astronomical
Algorithms but it is nearly out of print and copies in the USA sell for
insane prices. These guys still have reasonably priced stock.

https://www.firstlightoptics.com/books/astronomical-algorithms.html

(chapters 29 through 33 - assumes moderately advanced maths)

Bad news is it doesn\'t deal with terrestrial satellites only solar
system objects but the principles are the same it is just that there are
drag and oblateness corrections for orbiting the Earth in addition.

And also a much more significant correction for the observer being sat
on the surface of the Earth rather than at its centre. Objects in near
Earth orbit are subject to a lot of parallax from the ground.

Offhand I don\'t know of any code that does it very accurately (like the
GPS code does) but then you may not need great accuracy provided the
satellite positions are indicative of how many you have in the sky at
any one time. Never used any of these but worth a look:

https://listoffreeware.com/satellite-tracking-software-windows/

https://www.satsignal.eu/software/wxtrack.htm

I don\'t think it handles satellite ephemera, but for anyone interested
in Astronomy this package might prove useful:

<https://github.com/cosinekitty/astronomy>

A few lines of code can give you telescope pointing directions (alt/az)
from any point on earth to any object given its celestial coordinates,
for example.

I\'m sure the author would be appreciative of extension code to handle
satellites.

Clifford Heath.

 

[Chris Jones]

On 12/06/2022 20:46, Hul Tytus wrote:

Martin - thanks for the suggestion. I\'ll give Meeus\' book a try. Accuracy of
the orbital need not be great for this application, as you mention.
I looked at Meeus\' book once when seeking a procedure for calculating the
sun\'s position and was supprised at the lack of accurracy.

Huh? NIST has a program you can download here, and it is pretty
accurate. I have used it a lot:

https://midcdmz.nrel.gov/spa/

There is a report about it here:

http://www.nrel.gov/docs/fy08osti/34302.pdf

It says in the abstract that it uses Meeus\'s algorithm.

 

[Chris Jones]

On 12/06/2022 10:15, Hul Tytus wrote:

John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.

Unless you implement your own receiver, that isn\'t going to work
reliably. The receiver can pick and choose which satellites it includes
or excludes in its calculations and there is no guarantee that it will
pick the same ones at two different times, even if the same ones happen
to be visible. For the same reason, you can\'t use two ordinary consumer
GPS receivers to do differential GPS by just subtracting the known error
in the position solution of one station from the other station\'s
position solution - that won\'t work at all if they are using different
satellites.

About 15 years ago I recall finding a software GPS receiver somewhere on
the internet, and I\'m sure there have been more or better ones developed
since then. Perhaps that would suit your needs, as you could tweak its
behaviour, get it to print out the satellite positions, etc.

 

[Lasse Langwadt Christensen]

søndag den 12. juni 2022 kl. 15.40.57 UTC+2 skrev Chris Jones:

On 12/06/2022 10:15, Hul Tytus wrote:
John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.
Unless you implement your own receiver, that isn\'t going to work
reliably. The receiver can pick and choose which satellites it includes
or excludes in its calculations and there is no guarantee that it will
pick the same ones at two different times, even if the same ones happen
to be visible. For the same reason, you can\'t use two ordinary consumer
GPS receivers to do differential GPS by just subtracting the known error
in the position solution of one station from the other station\'s
position solution - that won\'t work at all if they are using different
satellites.

About 15 years ago I recall finding a software GPS receiver somewhere on
the internet, and I\'m sure there have been more or better ones developed
since then. Perhaps that would suit your needs, as you could tweak its
behaviour, get it to print out the satellite positions, etc.

https://www.rtl-sdr.com/rtl-sdr-tutorial-gps-decoding-plotting/

 

[Hul Tytus]

Martin the VSOP methods sound like what I was after, thanks for mentioning
it. The Predict program at qsl.net appears useful but the source is barred
by an indemnity clause in their \"terms of service\".

Hul

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 12/06/2022 11:46, Hul Tytus wrote:
Martin - thanks for the suggestion. I\'ll give Meeus\' book a try. Accuracy of
the orbital need not be great for this application, as you mention.
I looked at Meeus\' book once when seeking a procedure for calculating the
sun\'s position and was supprised at the lack of accurracy. Someone\'s keeping
their methods close to the vest.

The full methods for the solar system are published as VSOP82 onwards.
Current one is VSOP2013. It is a semianalytic fit to numerical
integration and incredibly accurate.

Observations of a pulsar that got really close to Jupiter found a
problem with the FORTRAN continuation cards (>10) generated by the
symbolic algebra program. For a moment it looked like relativity was not
predicting the right time delay for light passing close to Jupiter. But
it turned out that Jupiter wasn\'t where the theory said it was.

Fixed from VSOP87 onwards. That is good enough for most purposes...

Almost all planetarium programs use this VSOP method now.

https://en.wikipedia.org/wiki/VSOP_model

--
Regards,
Martin Brown

 

[Hul Tytus]

Martin the readings I\'ve recently taken are formed by waiting about 2 minutes
after the reciever has \"captured\" a useable number of sattelites and then averaging
all readings for 8 minutes. This has shown uniquely accurate (repeatible) readings
one day and some distinctly at variance on another. The objective now is to identify
the good days and also the bad days in order to avoid the latter. Averaging more
than the most basic method mentioned above would be counter to current intent, at
least at this point.

Hul



Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 12/06/2022 01:15, Hul Tytus wrote:
John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.

If you don\'t mind getting a biassed estimate then the minimum variance
estimate will weight down any sporadic glitches automatically.

Likewise for minimum 1-norm estimates (ie median rather than mean).

Unweighted least squares pays too much attention to the outliers.
(and the thing that is certain is that will have the odd one)

--
Regards,
Martin Brown

 

[rbowman]

On 06/12/2022 08:56 AM, Lasse Langwadt Christensen wrote:

søndag den 12. juni 2022 kl. 15.40.57 UTC+2 skrev Chris Jones:
On 12/06/2022 10:15, Hul Tytus wrote:
John I am looking at positions generated each second by one of Ublox\'s
9 series of GPS receivers. Some readings at a single location show (monday at
10, tues at 5..) good repeatability and some are noticebly off. The idea
is to see the satellite positions at the time of known readings, gain a feel
for good/bad satellite positions and use that to shedule further readings.
Unless you implement your own receiver, that isn\'t going to work
reliably. The receiver can pick and choose which satellites it includes
or excludes in its calculations and there is no guarantee that it will
pick the same ones at two different times, even if the same ones happen
to be visible. For the same reason, you can\'t use two ordinary consumer
GPS receivers to do differential GPS by just subtracting the known error
in the position solution of one station from the other station\'s
position solution - that won\'t work at all if they are using different
satellites.

About 15 years ago I recall finding a software GPS receiver somewhere on
the internet, and I\'m sure there have been more or better ones developed
since then. Perhaps that would suit your needs, as you could tweak its
behaviour, get it to print out the satellite positions, etc.

https://www.rtl-sdr.com/rtl-sdr-tutorial-gps-decoding-plotting/

Another project to get around to someday. I\'m currently using a rtl-sdr
dongle to pick up ADS-B information.