Re: [time-nuts] over-determined clock solution

[Poul-Henning Kamp]

In message , Mark Sims writes:

>All timing receivers (including Trimble) calculate an overdetermined
>clock solution if more than 4 sats are being tracked (and the signal
>meets their TRAIM quality level).   But, again, in Trimble-speak,
>"overdetermined clock mode" is what most manufacturers call "position
>hold" mode.  Position hold mode requires the receiver to have an
>accurate surveyed in position set in the receiver (and position
>hold mode/Trimble overdetermined clock mode cannot be used in mobile
>applications)

Weel...

"Overdetermined" just means that you have more equations than unknowns
so these days pretty much anything that comes out of your GNSS
receiver is "overdetermined":  A time+position calculated from
five or more sats is per definition overdetermined.

Position Hold just adds the constraint, "I'm not moving" to the
calculations, but if you are up to "funnier" math, less rigid
and often more useful constraints can also be used:

*  not moving faster than a pedestrian/bicyclist/boat/car

*  horizontal/vertical acceleration less than ...

*  horizontal/vertical jerk (= change of acceleration) less than ...

*  horizontal/vertical turning radius no less than ...

*  vertical speed less than ...

*  constrained to approximate surface of geoid (= boats)

*  constrained to surface of auxillary map

*  follows roads

*  acceleration constrained by data form accelerometer

*  etc.

Many receivers do one or more variants of these, some of them
autonomously guessing which one they should use.

But they usually call it, and implement it as, filtering, becausb
they don't think the hyperbolic math is "funnier" at all.

As a general rule of thumb: There are no exact solutions to hyperbolic
equations, you have to iterate your way to the answer.

Kalman filters are of course popular here, because of the widespread
misbelief that they dont need to be tuned.

But as an equally general rule of thump:  You get better results
by doing the hyperbolic equations than by slapping a filter on the
output.

Position Hold is one of the few constraints where the hyperbolic
math actually gets easier, because you only solve for a single
variable and everything else is constant.

But Position Hold is not the optimal algorithem, it's kind of a
hack, which is why the "hold position" to manys surprise only
needs to be precise to tens of meter.

What you _really_ want is to null out the average time resisuals
over long periods of time, with due attention to the anisotropic
propagation.

I tried a proof of concept, with some luck, by tweaking the position
hold coordinates to minimize the time residuals:

http://phk.freebsd.dk/raga/sneak/

But if you _really_ want to get fancy, the position hold coordinates
needs to be modelled as a function of time (day, year) to handle the
solar-forced ionospheric variations.

If instead you took the raw measurements, did the hyperbolic
iterations with the goal of minimizing your _time_ residuals, and
then filtered the heck out of the result afterwards, that would
happen automatically.

Alas, this is one of those projects that keep falling out through
the hard 1000 item limit of my TODO list...

Johns WebSDR is probably a near perfect platform for playing with
this...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] over-determined clock solution

[Mark Sims]

All timing receivers (including Trimble) calculate an overdetermined clock 
solution if more than 4 sats are being tracked (and the signal meets their 
TRAIM quality level).   But, again, in Trimble-speak,  "overdetermined clock 
mode" is what most manufacturers call "position hold" mode.  Position hold mode 
requires the receiver to have an accurate surveyed in position set in the 
receiver (and position hold mode/Trimble overdetermined clock mode cannot be 
used in mobile applications)
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Steve]

Thanks all for the info about the GPS over-determined clock solution, 
helps me much. Bill's suggestion to internet search the term absent the 
hyphen turns up numerous hits as well.


Steve, K8JQ


On 6/25/2016 2:10 PM, Bill Hawkins wrote:

Try overdetermined as one word. Also include GPS in the search string.
Google has many hits.

In timing receivers, once the position has been determined the receiver
switches to using timing information from all of the satellites that it
can see. Like the man with too many clocks, the clock time solution is
calculated from too many satellites.

That's what it looks like to me, anyway.

Bill Hawkins


-Original Message-
From: Steve
Sent: Saturday, June 25, 2016 9:08 AM

The phrase "over-determined clock solution" is used in the Trimble
Thunderbolt user manual in describing operation of the Thunderbolt GPS
receiver. The manual does not discuss the phrase in any detail,
appearing to assume the reader understands its meaning. An internet
search on "over-determined clock solution" did not turn up any
substantive hits.

What does "over-determined clock solution" mean?

Thanks.

Steve, K8JQ


___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.




___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Joseph Gwinn]

On Sat, 25 Jun 2016 22:00:25 -0400, time-nuts-requ...@febo.com wrote:
> 
> Message: 3
> Date: Sat, 25 Jun 2016 10:07:30 -0400
> From: Steve <stev...@suddenlink.net>
> To: Discussion of precise time and frequency measurement
>   <time-nuts@febo.com>
> Subject: [time-nuts] over-determined clock solution
> Message-ID: <9d1c7e89-c192-36bc-8f93-7ebac3d29...@suddenlink.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> The phrase "over-determined clock solution" is used in the Trimble 
> Thunderbolt user manual in describing operation of the Thunderbolt GPS 
> receiver. The manual does not discuss the phrase in any detail, 
> appearing to assume the reader understands its meaning. An internet 
> search on "over-determined clock solution" did not turn up any 
> substantive hits.
> 
> What does "over-determined clock solution" mean?
> 
> Thanks.
> 
> Steve, K8JQ
> 
> End of time-nuts Digest, Vol 143, Issue 41
> **

As others have said, it means that there are more satellites than the 
minimum required to compute a fix.  The minimum for a full fix is four, 
to cover x, y, z, and t.

The term "over determined" comes from Linear Algebra, and this is the 
best place to look.  

I am partial to Intro to Linear Algebra, 5th edition, by Gilbert 
Strang:  
<http://www.wellesleycambridge.com/images/linearalgebra5_Front.jpg>.  
Strang is a MIT Math Prof, and his lectures are all available gratis on 
the MIT website.

The classic application leading to an over determined linear system is 
least-squared fitting.

Joe Gwinn
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Azelio Boriani]

In this receiver mode all the satellites are used to compute the
timing solution. See page 80 of the 2012 Thunderbolt-E manual:



This mode is available when the position of the antenna is known and
is stationary. Timing receivers usually take care of the initial
position survey at power-on and enter this mode automatically after
the survey is over.

On Sat, Jun 25, 2016 at 4:07 PM, Steve  wrote:
> The phrase "over-determined clock solution" is used in the Trimble
> Thunderbolt user manual in describing operation of the Thunderbolt GPS
> receiver. The manual does not discuss the phrase in any detail, appearing to
> assume the reader understands its meaning. An internet search on
> "over-determined clock solution" did not turn up any substantive hits.
>
> What does "over-determined clock solution" mean?
>
> Thanks.
>
> Steve, K8JQ
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Bill Hawkins]

Try overdetermined as one word. Also include GPS in the search string.
Google has many hits.

In timing receivers, once the position has been determined the receiver
switches to using timing information from all of the satellites that it
can see. Like the man with too many clocks, the clock time solution is
calculated from too many satellites.

That's what it looks like to me, anyway.

Bill Hawkins


-Original Message-
From: Steve
Sent: Saturday, June 25, 2016 9:08 AM

The phrase "over-determined clock solution" is used in the Trimble
Thunderbolt user manual in describing operation of the Thunderbolt GPS
receiver. The manual does not discuss the phrase in any detail,
appearing to assume the reader understands its meaning. An internet
search on "over-determined clock solution" did not turn up any
substantive hits.

What does "over-determined clock solution" mean?

Thanks.

Steve, K8JQ


___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Oz-in-DFW]

On 6/25/2016 9:07 AM, Steve wrote:
> The phrase "over-determined clock solution" is used in the Trimble
> Thunderbolt user manual in describing operation of the Thunderbolt GPS
> receiver. The manual does not discuss the phrase in any detail,
> appearing to assume the reader understands its meaning. An internet
> search on "over-determined clock solution" did not turn up any
> substantive hits.
>
> What does "over-determined clock solution" mean?
>
> Thanks.
>
> Steve, K8JQ
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

Generally this means that more than the four required signals are used
to determine the result.  Some sort of statisical fitler is used to
reduce the resulting measurement errors.

-- 
mailto:o...@ozindfw.net
Oz
POB 93167 
Southlake, TX 76092 (Near DFW Airport) 



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] over-determined clock solution

[Mark Sims]

Trimble can operate in a 3D positioning operation mode that works that way.   
But their "overdetermined clock" mode is what most people call "position hold" 
mode.  Set the receiver to "overdetermined clock", and the lat/lon/alt 
coordinates it sends never change.


As far as I know, it simply means that there are more satellites in view than 
needed for a fully accurate time to be determined. If it needs four sats to 
come up with a valid location plus time, it has five or more.   

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] over-determined clock solution

[Mark Sims]

It is basically what most people call "position hold mode" where the receiver 
has known (and accurate) fixed coordinates.  With lat/lon/alt known,  it can 
solve for time with just one satellite visible.  Or, if more than one sat is 
visible, its time solutions can be more accurate because noise in the 
lat/lon/alt calculations won't affect the time solutions.  The gotcha is any 
error in your fixed position coordinates directly contribute to time errors 
(figure 1 nanosecond per foot of error).
   
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Hal Murray]

stev...@suddenlink.net said:
> The phrase "over-determined clock solution" is used in the Trimble
> Thunderbolt user manual in describing operation of the Thunderbolt GPS
> receiver.  

> What does "over-determined clock solution" mean?

You are trying to solve for X, Y, Z, and T.  (or the polar equivalents)  4 
unknowns takes 4 equations.  You get one equation from each satellite, so you 
need 4 satellites to get an answer.

If you have more satellites, you have more information than you need, hence 
the solution is over-determined.


-- 
These are my opinions.  I hate spam.



___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] over-determined clock solution

[Bob Camp]

Hi

As far as I know, it simply means that there are more satellites in view than 
needed for a fully accurate 
time to be determined. If it needs four sats to come up with a valid location 
plus time, it has five or
more. If it has five but is not happy with the location solution (still in 
survey etc) it likely is not going to be
happy with the time solution. At the other end of the status empire, you have 
TRAIM fail (or whatever 
a specific manufacturer calls it).  In that case you have multiple sats, but 
they don’t agree well enough
to figure out what time it is at all. 

Bob


> On Jun 25, 2016, at 10:07 AM, Steve  wrote:
> 
> The phrase "over-determined clock solution" is used in the Trimble 
> Thunderbolt user manual in describing operation of the Thunderbolt GPS 
> receiver. The manual does not discuss the phrase in any detail, appearing to 
> assume the reader understands its meaning. An internet search on 
> "over-determined clock solution" did not turn up any substantive hits.
> 
> What does "over-determined clock solution" mean?
> 
> Thanks.
> 
> Steve, K8JQ
> 
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] over-determined clock solution

[Steve]

The phrase "over-determined clock solution" is used in the Trimble 
Thunderbolt user manual in describing operation of the Thunderbolt GPS 
receiver. The manual does not discuss the phrase in any detail, 
appearing to assume the reader understands its meaning. An internet 
search on "over-determined clock solution" did not turn up any 
substantive hits.


What does "over-determined clock solution" mean?

Thanks.

Steve, K8JQ

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.