GPS position survey
On 5 May 2013 12:28, Sarah White kuzetsa@gmail.com wrote:
I myself did a sampling over a period of 1 million samples
(actually, it was a value of 2^20, not exactly 1 "million")
quickest it could have completed such a survey is 12+ days
... However, I had "masks" set for elevation, signal, etc.
(resulted in occasional periods when there was no "lock")
Thank you Sarah for your input!
I might do that. For what I've read regarding timing applications the
receiver should pick only satellites with high elevation but for
position surveying a good geometry is better.
Could you give your input regarding elevation masks and other
parameters to do a good survey?
Regards,
Miguel
If you are talking about using this with NTP. I don't know if you
have a choice. The Trimble receiver is going to do whatever it is
going to do when you power it up. Software running on a PC can
perform a 24 hour survey and report the location but the "Type 29"
driver in NTP has no way to tell the Trimble receiver what to do on
power up. And there is no way to specify a location you have surveyed
by some other means.
Perhaps the Trimble GPS has some way to program it's FLASH Rom with
changed parameters but NTP only reads the packets. It does not send
any. Can LH download a surveyed location r change the length of the
survey? NTP can't do any of that
Other NTP drivers such as the Type 30 Motorola driver are more
flexible. Those alow you to specify a lat, long that was surveyed or
have the receiver do a survey. The type-30 Motorola driver is a lot
more configurable.
But as was said, light travels about 30cm/nanosecond and NTP works in
microseconds. So your location can be "off" by 1000 times 30cm before
NTP will care. So 3 or 4 meters of location error will not matter and
the 2,000 point self survey will be good enough.
But if yo really so want nanosecond level timing, then you need to
care about the survey
On Sun, May 5, 2013 at 4:28 AM, Sarah White kuzetsa@gmail.com wrote:
On 5/5/2013 6:35 AM, Miguel Barbosa Gonçalves wrote:
Hi fellow time nuts!
I've recently bought a Trimble Acutime gold that will be used as a
reference clock for a NTP server.
This receiver has the possibility of averaging it's position before
entering what Trimble calls the overdetermined clock state. The
default is to average the position with 2000 fixes.
What do you believe is a good number of fixes for the survey in this case?
Cheers,
Miguel
Accurate position might be important. Light travels a distance of
something like 29.9792 centimeters per nanosecond
You might find the results of this study to be helpful:
http://www.syz.com/gps/gpsaveraging.html
I myself did a sampling over a period of 1 million samples
(actually, it was a value of 2^20, not exactly 1 "million")
quickest it could have completed such a survey is 12+ days
... However, I had "masks" set for elevation, signal, etc.
(resulted in occasional periods when there was no "lock")
I'm quite satisfied / happy with the results :)
hope this helps?
--Sarah
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.
--
Chris Albertson
Redondo Beach, California
Hi Chris!
On 06/05/2013, at 01:21, Chris Albertson albertson.chris@gmail.com wrote:
If you are talking about using this with NTP. I don't know if you
have a choice. The Trimble receiver is going to do whatever it is
going to do when you power it up. Software running on a PC can
perform a 24 hour survey and report the location but the "Type 29"
driver in NTP has no way to tell the Trimble receiver what to do on
power up. And there is no way to specify a location you have surveyed
by some other means.
What I am doing at the moment is connecting Trimble's port A (timing
port) to NTP and configuring the receiver using a Windows laptop
through port B. I can connect to port B occasionally to check the
receivers health. The receiver has its configuration stored in an
EPROM so it will just work anytime unless the configuration gets
corrupted.
After the survey ends the position can be optionally stored to the
EPROM. Also, if the antenna changes its position more than 1000 meters
a new self-survey will run automatically.
Perhaps the Trimble GPS has some way to program it's FLASH Rom with
changed parameters but NTP only reads the packets. It does not send
any. Can LH download a surveyed location r change the length of the
survey? NTP can't do any of that
It does. It is available on the Trmble's FTP site.
Other NTP drivers such as the Type 30 Motorola driver are more
flexible. Those alow you to specify a lat, long that was surveyed or
have the receiver do a survey. The type-30 Motorola driver is a lot
more configurable.
The Trimble software is very nice and allows one thing the Motorola
NTP driver doesn't allow if I remember correctly. On the Trimble I can
choose the number of fixes for the survey and can watch it run while
NTP is receiving time. I can't do this on an Oncore because it only
has one port.
But as was said, light travels about 30cm/nanosecond and NTP works in
microseconds. So your location can be "off" by 1000 times 30cm before
NTP will care. So 3 or 4 meters of location error will not matter and
the 2,000 point self survey will be good enough.
When surveying accuracy of the PPS will be around 1 us. The accuracy
will obviously increase when the survey ends.
But if yo really so want nanosecond level timing, then you need to
care about the survey
Agree!
Cheers,
Miguel
So this is different from the Thunderbolt, even if they both use the
same serial protocol or can the t-bolt also have it's flash rom
programmed from a PC?
The bottle neck in the system in the uncertainty in the interrupt
latency on the PC where NTP runs. After all this I doubt you can
captures the PPS to better than 1 uS.
For a long time I've been wnting to build an external counter for NTP.
But it would have to use some very fast logic family.
On Sun, May 5, 2013 at 6:26 PM, Miguel Barbosa Gonçalves m@mbg.pt wrote:
Hi Chris!
On 06/05/2013, at 01:21, Chris Albertson albertson.chris@gmail.com wrote:
If you are talking about using this with NTP. I don't know if you
have a choice. The Trimble receiver is going to do whatever it is
going to do when you power it up. Software running on a PC can
perform a 24 hour survey and report the location but the "Type 29"
driver in NTP has no way to tell the Trimble receiver what to do on
power up. And there is no way to specify a location you have surveyed
by some other means.
What I am doing at the moment is connecting Trimble's port A (timing
port) to NTP and configuring the receiver using a Windows laptop
through port B. I can connect to port B occasionally to check the
receivers health. The receiver has its configuration stored in an
EPROM so it will just work anytime unless the configuration gets
corrupted.
After the survey ends the position can be optionally stored to the
EPROM. Also, if the antenna changes its position more than 1000 meters
a new self-survey will run automatically.
Perhaps the Trimble GPS has some way to program it's FLASH Rom with
changed parameters but NTP only reads the packets. It does not send
any. Can LH download a surveyed location r change the length of the
survey? NTP can't do any of that
It does. It is available on the Trmble's FTP site.
Other NTP drivers such as the Type 30 Motorola driver are more
flexible. Those alow you to specify a lat, long that was surveyed or
have the receiver do a survey. The type-30 Motorola driver is a lot
more configurable.
The Trimble software is very nice and allows one thing the Motorola
NTP driver doesn't allow if I remember correctly. On the Trimble I can
choose the number of fixes for the survey and can watch it run while
NTP is receiving time. I can't do this on an Oncore because it only
has one port.
But as was said, light travels about 30cm/nanosecond and NTP works in
microseconds. So your location can be "off" by 1000 times 30cm before
NTP will care. So 3 or 4 meters of location error will not matter and
the 2,000 point self survey will be good enough.
When surveying accuracy of the PPS will be around 1 us. The accuracy
will obviously increase when the survey ends.
But if yo really so want nanosecond level timing, then you need to
care about the survey
Agree!
Cheers,
Miguel
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.
--
Chris Albertson
Redondo Beach, California
Isn't the other half of the question how useful the information is to the OS? That is how is the time integrated with the application using it. Even if the RTCs had perfect sync, would two apps attempting to read the clock get the same time value in a multitasking system?
I've been looking for the stat on the London stock exchange, which runs on Suse Enterprise. I recall they claimed 100us time stamp accuracy, but can't find a source.
I thought PTP would be more accurate than NTP, but the consensus of the hive is they are equally good.
If you follow ADS-B/mode-s aircraft tracking, a number of vendors are using MLAT techniques to detect the aircraft location in the case of mode-s, and to detect spoofing in the case of ADS-B. Some use a transmitter that all the sites can receive, that is they make their own time sync scheme. But others are using GPSDO. But I assume they time stamp the aircraft signal reception in their own hardware.
-----Original Message-----
From: Chris Albertson albertson.chris@gmail.com
Sender: time-nuts-bounces@febo.com
Date: Sun, 5 May 2013 20:40:41
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] GPS position survey
So this is different from the Thunderbolt, even if they both use the
same serial protocol or can the t-bolt also have it's flash rom
programmed from a PC?
The bottle neck in the system in the uncertainty in the interrupt
latency on the PC where NTP runs. After all this I doubt you can
captures the PPS to better than 1 uS.
For a long time I've been wnting to build an external counter for NTP.
But it would have to use some very fast logic family.
On Sun, May 5, 2013 at 6:26 PM, Miguel Barbosa Gonçalves m@mbg.pt wrote:
Hi Chris!
On 06/05/2013, at 01:21, Chris Albertson albertson.chris@gmail.com wrote:
If you are talking about using this with NTP. I don't know if you
have a choice. The Trimble receiver is going to do whatever it is
going to do when you power it up. Software running on a PC can
perform a 24 hour survey and report the location but the "Type 29"
driver in NTP has no way to tell the Trimble receiver what to do on
power up. And there is no way to specify a location you have surveyed
by some other means.
What I am doing at the moment is connecting Trimble's port A (timing
port) to NTP and configuring the receiver using a Windows laptop
through port B. I can connect to port B occasionally to check the
receivers health. The receiver has its configuration stored in an
EPROM so it will just work anytime unless the configuration gets
corrupted.
After the survey ends the position can be optionally stored to the
EPROM. Also, if the antenna changes its position more than 1000 meters
a new self-survey will run automatically.
Perhaps the Trimble GPS has some way to program it's FLASH Rom with
changed parameters but NTP only reads the packets. It does not send
any. Can LH download a surveyed location r change the length of the
survey? NTP can't do any of that
It does. It is available on the Trmble's FTP site.
Other NTP drivers such as the Type 30 Motorola driver are more
flexible. Those alow you to specify a lat, long that was surveyed or
have the receiver do a survey. The type-30 Motorola driver is a lot
more configurable.
The Trimble software is very nice and allows one thing the Motorola
NTP driver doesn't allow if I remember correctly. On the Trimble I can
choose the number of fixes for the survey and can watch it run while
NTP is receiving time. I can't do this on an Oncore because it only
has one port.
But as was said, light travels about 30cm/nanosecond and NTP works in
microseconds. So your location can be "off" by 1000 times 30cm before
NTP will care. So 3 or 4 meters of location error will not matter and
the 2,000 point self survey will be good enough.
When surveying accuracy of the PPS will be around 1 us. The accuracy
will obviously increase when the survey ends.
But if yo really so want nanosecond level timing, then you need to
care about the survey
Agree!
Cheers,
Miguel
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.
--
Chris Albertson
Redondo Beach, California
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.