[time-nuts] GPS position survey
Earth circumference is around 25,000 miles - 132E6 feet. 24 bit mantissa (23 bits plus sign) gives a resolution in this application of around 15.7 feet since negative measurements don't apply. --- Oh... 24 bit mantissa should give 1.25 m resolution if my headcounting is about right ___ 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] GPS position survey
In message 518733c4.1020...@gmail.com, Sarah White writes: On 5/6/2013 12:29 AM, Mark Sims wrote: The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. You can probably do even better than that: Weigh the summing by DOP. That gave me a factor two or so, because it reduced the weight of samples suffering from multipath and other ailments. -- 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.
Re: [time-nuts] GPS position survey
A subtle point: The GPS satellite orbits are controlled so that their (nominal) ground tracks precisely repeat every day. To make this work, their day is not a standard 24-hour day but a sidereal day lasting 23 hours, 56 minutes, and about 4 seconds. The satellites actually go around the earth twice in that time, so their orbits take 11 hours and 58+ minutes, but the earth is only halfway around after the first orbit, so the ground tracks only repeat every other orbit. The ground tracks repeat so that multipath errors can be averaged out by taking data in multiples of one sidereal day. If you want to get the most accurate position by averaging satellite data, do your average in multiples of 86164 seconds (sidereal day) rather than 86400 seconds (24 hours). It also helps to take data during a time when the weather is relatively constant. In particular, avoid precipitation. Cheers! --Stu ___ 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] GPS position survey
I was using 90 deg = 1000 m as approximation. I forgot about the sign but as I recall the leading 1 is surpressed. 360 deg on 25 bits. Reducing approx gave me 10 and 3 bits. Cheers Magnus Originalmeddelande Från: Mark Sims hol...@hotmail.com Datum: Till: time-nuts@febo.com Rubrik: [time-nuts] GPS position survey Earth circumference is around 25,000 miles - 132E6 feet. 24 bit mantissa (23 bits plus sign) gives a resolution in this application of around 15.7 feet since negative measurements don't apply. --- Oh... 24 bit mantissa should give 1.25 m resolution if my headcounting is about right ___ 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] GPS position survey
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 ___ 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] GPS position survey
In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: 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? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. -- 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.
Re: [time-nuts] GPS position survey
On 5 May 2013 11:51, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: 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? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. Hi Poul! So you think a full day of position survey will be better? The receiver will still output time while surveying so doing it for a long time is not a problem. Appreciate your input. 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.
Re: [time-nuts] GPS position survey
Hi Something like 48 hours is a good idea *if* you have the time to do them. Bob On May 5, 2013, at 7:34 AM, Miguel Barbosa Gonçalves m...@mbg.pt wrote: On 5 May 2013 11:51, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: 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? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. Hi Poul! So you think a full day of position survey will be better? The receiver will still output time while surveying so doing it for a long time is not a problem. Appreciate your input. 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. ___ 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] GPS position survey
If the only use of the GPS receiver is to drive NTP, then 2,000 seconds is long enough NTP runs at the microsecond level and the tiny remaining error after 2000 seconds will never be noticed by NTP. However if you are really nuts and want to do the best you can then let it run for 12 hours. That is one orbital period. That said, what matters FAR more is that the antenna have a good view of the full sky and be far away from anything that can reflect radio waves. This pretty much means the antenna should be on a pipe mast on the roof. (a 3/4 inch pipe with a pipe flange on top). If you have not done this then don't bother with a 12 hour survey as you'd be worrying about details that don't matter. On Sun, May 5, 2013 at 3:35 AM, Miguel Barbosa Gonçalves m...@mbg.pt 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 ___ 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.
Re: [time-nuts] GPS position survey
In message caedntmsjwt0suxbzdrnz3enyw6xhuvlhvmfw_cmq5r8etay...@mail.gmail.com , =?ISO-8859-1?Q?Miguel_Barbosa_Gon=E7alves?= writes: So you think a full day of position survey will be better? I don't know if it is as sensitive on your lattitude as mine (56N) but here N*12 hours works best, for as big a N as you have patience for, up to about 10 -- 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.
Re: [time-nuts] GPS position survey
When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? -- Chuck Forsberg WA7KGX c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 ___ 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] GPS position survey
On 5 May 2013 20:18, Chuck Forsberg WA7KGX N2469R c...@omen.com wrote: When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? I don't know about Thunderbolt but on my Acutime Gold the Windows software sends the restart survey command to the antenna and the antenna does everything by itself. I can even turn off the Windows monitoring software. HTH, 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.
Re: [time-nuts] GPS position survey
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.
Re: [time-nuts] GPS position survey
Le 5 mai 2013 à 21:18, Chuck Forsberg WA7KGX N2469R a écrit : When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? Good question. I would have thought that once started, the survey would complete even though LH was stopped/started, but that does not seem to be the case. I started a survey yesterday and stopped LH once I saw that it was proceeding. Three hours later I restarted LH, expecting to see the progress, but the survey was not running. Now I have left LH active will the survey completes. ___ 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] GPS position survey
On 5 May 2013 12:28, Sarah White kuze...@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 ___ 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] GPS position survey
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 kuze...@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 ___ 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] GPS position survey
Hi Chris! On 06/05/2013, at 01:21, Chris Albertson albertson.ch...@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.
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.ch...@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.
Re: [time-nuts] GPS position survey
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.ch...@gmail.com Sender: time-nuts-boun...@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.ch...@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. ___ 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] GPS position survey
The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. ___ 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] GPS position survey
On 5/6/2013 12:29 AM, Mark Sims wrote: The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. Wow, thanks. I didn't realize that. This approach you described from lady heather sounds really cool from my time-nut perspective. I used the trimble provided utility for the survery. Really not sure if the internal firmware did the calculation and/or filtering, or what method was used. --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.
Re: [time-nuts] GPS position survey
Oh... 24 bit mantissa should give 1.25 m resolution if my headcounting is about right. Thats about 4 ns. Royal kludge indeed. Cheers Magnus Originalmeddelande Från: Mark Sims hol...@hotmail.com Datum: Till: time-nuts@febo.com Rubrik: [time-nuts] GPS position survey The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. ___ 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.
