Empathy List Archives

OP

Ole Petter Ronningen

Mon, Dec 15, 2014 9:03 AM

Hello, all

I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna
through an HP 58516 splitter. I notice that when I powercycle the GPSDOs
(which I generally try to avoid), the position they come up with differs
from time to time in at least the last three digits (and height in
particular varies with up to 30m).

I would like to get a better idea of what my actualt antenna location is,
so that I can manually set the position in the GPSDOs. For that purpose I
set up a Ublox M8N with logging in U-center, and I've collected about 250K
readings over several days. For each reading I also log number of SV's
used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end
up with a subset of really good fixes.The idea is then to average the "best
readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2) How
do I average the numbers? I can not put my finger on it but it "feels
wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

Thank you!
Ole P

Hello, all I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna through an HP 58516 splitter. I notice that when I powercycle the GPSDOs (which I generally try to avoid), the position they come up with differs from time to time in at least the last three digits (and height in particular varies with up to 30m). I would like to get a better idea of what my actualt antenna location is, so that I can manually set the position in the GPSDOs. For that purpose I set up a Ublox M8N with logging in U-center, and I've collected about 250K readings over several days. For each reading I also log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end up with a subset of really good fixes.The idea is then to average the "best readings" and use that as my position. My question is twofold; 1) is this for some reason a bad idea? And 2) How do I average the numbers? I can not put my finger on it but it "feels wrong" to average lat, long and height independently. Any hints are greatly appreciated. Thank you! Ole P

TS

Tim Shoppa

Mon, Dec 15, 2014 11:43 AM

I would recommend determining your terrain's elevation using a topo map and
estimating or measuring antennas height above ground. And then excluding
survey results with wacko altitudes before averaging.

While we often set the elevation angle mask high for timing purposes, for
survey purposes especially altitude it will likely be best to do survey
with no or very low (10 degree default?) elevation mask. The Z3801A manual
tells how to set elevation mask for at least some of your units.

Tim N3QE

On Mon, Dec 15, 2014 at 4:03 AM, Ole Petter Ronningen olepr01@gmail.com
wrote:

Hello, all

I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna
through an HP 58516 splitter. I notice that when I powercycle the GPSDOs
(which I generally try to avoid), the position they come up with differs
from time to time in at least the last three digits (and height in
particular varies with up to 30m).

I would like to get a better idea of what my actualt antenna location is,
so that I can manually set the position in the GPSDOs. For that purpose I
set up a Ublox M8N with logging in U-center, and I've collected about 250K
readings over several days. For each reading I also log number of SV's
used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end
up with a subset of really good fixes.The idea is then to average the "best
readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2) How
do I average the numbers? I can not put my finger on it but it "feels
wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

Thank you!
Ole P

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I would recommend determining your terrain's elevation using a topo map and estimating or measuring antennas height above ground. And then excluding survey results with wacko altitudes before averaging. While we often set the elevation angle mask high for timing purposes, for survey purposes especially altitude it will likely be best to do survey with no or very low (10 degree default?) elevation mask. The Z3801A manual tells how to set elevation mask for at least some of your units. Tim N3QE On Mon, Dec 15, 2014 at 4:03 AM, Ole Petter Ronningen <olepr01@gmail.com> wrote: > > Hello, all > > I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna > through an HP 58516 splitter. I notice that when I powercycle the GPSDOs > (which I generally try to avoid), the position they come up with differs > from time to time in at least the last three digits (and height in > particular varies with up to 30m). > > I would like to get a better idea of what my actualt antenna location is, > so that I can manually set the position in the GPSDOs. For that purpose I > set up a Ublox M8N with logging in U-center, and I've collected about 250K > readings over several days. For each reading I also log number of SV's > used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end > up with a subset of really good fixes.The idea is then to average the "best > readings" and use that as my position. > > My question is twofold; 1) is this for some reason a bad idea? And 2) How > do I average the numbers? I can not put my finger on it but it "feels > wrong" to average lat, long and height independently. > > Any hints are greatly appreciated. > > Thank you! > Ole P > _______________________________________________ > 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. >

AB

Azelio Boriani

Mon, Dec 15, 2014 3:52 PM

The Ublox M8N can send out raw measurements with messages TRK-MEAS and
TRK-SFRBX for observation and navigation data: you can postprocess
them to improve the accuracy.
http://www.rtklib.com/rtklib_support.htm

On Mon, Dec 15, 2014 at 12:43 PM, Tim Shoppa tshoppa@gmail.com wrote:

I would recommend determining your terrain's elevation using a topo map and
estimating or measuring antennas height above ground. And then excluding
survey results with wacko altitudes before averaging.

While we often set the elevation angle mask high for timing purposes, for
survey purposes especially altitude it will likely be best to do survey
with no or very low (10 degree default?) elevation mask. The Z3801A manual
tells how to set elevation mask for at least some of your units.

Tim N3QE

On Mon, Dec 15, 2014 at 4:03 AM, Ole Petter Ronningen olepr01@gmail.com
wrote:

Hello, all

I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna
through an HP 58516 splitter. I notice that when I powercycle the GPSDOs
(which I generally try to avoid), the position they come up with differs
from time to time in at least the last three digits (and height in
particular varies with up to 30m).

I would like to get a better idea of what my actualt antenna location is,
so that I can manually set the position in the GPSDOs. For that purpose I
set up a Ublox M8N with logging in U-center, and I've collected about 250K
readings over several days. For each reading I also log number of SV's
used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end
up with a subset of really good fixes.The idea is then to average the "best
readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2) How
do I average the numbers? I can not put my finger on it but it "feels
wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

Thank you!
Ole P

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.

The Ublox M8N can send out raw measurements with messages TRK-MEAS and TRK-SFRBX for observation and navigation data: you can postprocess them to improve the accuracy. <http://www.rtklib.com/rtklib_support.htm> On Mon, Dec 15, 2014 at 12:43 PM, Tim Shoppa <tshoppa@gmail.com> wrote: > I would recommend determining your terrain's elevation using a topo map and > estimating or measuring antennas height above ground. And then excluding > survey results with wacko altitudes before averaging. > > While we often set the elevation angle mask high for timing purposes, for > survey purposes especially altitude it will likely be best to do survey > with no or very low (10 degree default?) elevation mask. The Z3801A manual > tells how to set elevation mask for at least some of your units. > > Tim N3QE > > On Mon, Dec 15, 2014 at 4:03 AM, Ole Petter Ronningen <olepr01@gmail.com> > wrote: >> >> Hello, all >> >> I have a couple of GPSDOs (KS, z3805a) hooked up to a fixed outdoor antenna >> through an HP 58516 splitter. I notice that when I powercycle the GPSDOs >> (which I generally try to avoid), the position they come up with differs >> from time to time in at least the last three digits (and height in >> particular varies with up to 30m). >> >> I would like to get a better idea of what my actualt antenna location is, >> so that I can manually set the position in the GPSDOs. For that purpose I >> set up a Ublox M8N with logging in U-center, and I've collected about 250K >> readings over several days. For each reading I also log number of SV's >> used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end >> up with a subset of really good fixes.The idea is then to average the "best >> readings" and use that as my position. >> >> My question is twofold; 1) is this for some reason a bad idea? And 2) How >> do I average the numbers? I can not put my finger on it but it "feels >> wrong" to average lat, long and height independently. >> >> Any hints are greatly appreciated. >> >> Thank you! >> Ole P >> _______________________________________________ >> 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.

P

Paul

Mon, Dec 15, 2014 4:36 PM

On Mon, Dec 15, 2014 at 10:52 AM, Azelio Boriani azelio.boriani@gmail.com
wrote:

The Ublox M8N can send out raw measurements with messages TRK-MEAS and
TRK-SFRBX for observation and navigation data: you can postprocess
them to improve the accuracy.

And searching the archives for rtklib should find some relevant posts with
pointers to post-processing. Naturally the output of rtklib doesn't quite
agree with the Canadian (CSRS-PPP) results although that could just be
operator error.

On Mon, Dec 15, 2014 at 10:52 AM, Azelio Boriani <azelio.boriani@gmail.com> wrote: > The Ublox M8N can send out raw measurements with messages TRK-MEAS and > TRK-SFRBX for observation and navigation data: you can postprocess > them to improve the accuracy. > And searching the archives for rtklib should find some relevant posts with pointers to post-processing. Naturally the output of rtklib doesn't quite agree with the Canadian (CSRS-PPP) results although that could just be operator error.

BH

Bill Hawkins

Tue, Dec 16, 2014 12:19 AM

This may be one of those cases where the human brain's ability to see
patterns would help to see the distribution and eliminate outliers. Plot
a manageable set of X and Y points, and another set of X and Z points.

To make the three dimensions plot as one in a statistical distribution
(bell) curve, use the magnitude of the vector.

What do the surveyors instruments do that can get them down to a few
centimeters in half an hour?

You might also want to study what's been said about the causes of
variance. The atmosphere is not uniform.

Consider the relative effect of position on time, where one foot or 30
cm is equivalent to 10E-9 second.

Also consider the 'averaging' period of the PLL filter in the
disciplined oscillator.

I'm no expert, especially not in math. These hints are thoughts that
come to mind.

Bill Hawkins

-----Original Message-----
From: Ole Petter Ronningen
Sent: Monday, December 15, 2014 3:04 AM

I would like to get a better idea of what my actualt antenna location
is, so that I can manually set the position in the GPSDOs. For that
purpose I set up a Ublox M8N with logging in U-center, and I've
collected about 250K readings over several days. For each reading I also
log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would
filter the list and end up with a subset of really good fixes.The idea
is then to average the "best readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2)
How do I average the numbers? I can not put my finger on it but it
"feels wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

This may be one of those cases where the human brain's ability to see patterns would help to see the distribution and eliminate outliers. Plot a manageable set of X and Y points, and another set of X and Z points. To make the three dimensions plot as one in a statistical distribution (bell) curve, use the magnitude of the vector. What do the surveyors instruments do that can get them down to a few centimeters in half an hour? You might also want to study what's been said about the causes of variance. The atmosphere is not uniform. Consider the relative effect of position on time, where one foot or 30 cm is equivalent to 10E-9 second. Also consider the 'averaging' period of the PLL filter in the disciplined oscillator. I'm no expert, especially not in math. These hints are thoughts that come to mind. Bill Hawkins -----Original Message----- From: Ole Petter Ronningen Sent: Monday, December 15, 2014 3:04 AM I would like to get a better idea of what my actualt antenna location is, so that I can manually set the position in the GPSDOs. For that purpose I set up a Ublox M8N with logging in U-center, and I've collected about 250K readings over several days. For each reading I also log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would filter the list and end up with a subset of really good fixes.The idea is then to average the "best readings" and use that as my position. My question is twofold; 1) is this for some reason a bad idea? And 2) How do I average the numbers? I can not put my finger on it but it "feels wrong" to average lat, long and height independently. Any hints are greatly appreciated.

BC

Bob Camp

Tue, Dec 16, 2014 12:39 AM

Hi

On Dec 15, 2014, at 7:19 PM, Bill Hawkins bill@iaxs.net wrote:

This may be one of those cases where the human brain's ability to see
patterns would help to see the distribution and eliminate outliers. Plot
a manageable set of X and Y points, and another set of X and Z points.

yup

To make the three dimensions plot as one in a statistical distribution
(bell) curve, use the magnitude of the vector.

What do the surveyors instruments do that can get them down to a few
centimeters in half an hour?

The ones around here use a survey grade GPS and log the data to a file. They do a bunch of post processing to get the solution to a desired level of accuracy. Last time I had it done, they had more fun looking at the GPSDO’s than running their fancy GPS.

You might also want to study what's been said about the causes of
variance. The atmosphere is not uniform.

Ionospheric issues are one of the things that gets corrected for to make a more accurate result.

Consider the relative effect of position on time, where one foot or 30
cm is equivalent to 10E-9 second.

…. and some of the errors between solutions are > 10 feet.

Also consider the 'averaging' period of the PLL filter in the
disciplined oscillator.

The problem shows up when the GPS constellation is in a configuration that accentuates the error. That’s often a 12 / 24 / 48 hour sort of thing.

Bob

I'm no expert, especially not in math. These hints are thoughts that
come to mind.

Bill Hawkins

-----Original Message-----
From: Ole Petter Ronningen
Sent: Monday, December 15, 2014 3:04 AM

I would like to get a better idea of what my actualt antenna location
is, so that I can manually set the position in the GPSDOs. For that
purpose I set up a Ublox M8N with logging in U-center, and I've
collected about 250K readings over several days. For each reading I also
log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would
filter the list and end up with a subset of really good fixes.The idea
is then to average the "best readings" and use that as my position.

My question is twofold; 1) is this for some reason a bad idea? And 2)
How do I average the numbers? I can not put my finger on it but it
"feels wrong" to average lat, long and height independently.

Any hints are greatly appreciated.

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.

Hi > On Dec 15, 2014, at 7:19 PM, Bill Hawkins <bill@iaxs.net> wrote: > > This may be one of those cases where the human brain's ability to see > patterns would help to see the distribution and eliminate outliers. Plot > a manageable set of X and Y points, and another set of X and Z points. yup > > To make the three dimensions plot as one in a statistical distribution > (bell) curve, use the magnitude of the vector. > > What do the surveyors instruments do that can get them down to a few > centimeters in half an hour? The ones around here use a survey grade GPS and log the data to a file. They do a bunch of post processing to get the solution to a desired level of accuracy. Last time I had it done, they had more fun looking at the GPSDO’s than running their fancy GPS. > > You might also want to study what's been said about the causes of > variance. The atmosphere is not uniform. Ionospheric issues are one of the things that gets corrected for to make a more accurate result. > > Consider the relative effect of position on time, where one foot or 30 > cm is equivalent to 10E-9 second. …. and some of the errors between solutions are > 10 feet. > > Also consider the 'averaging' period of the PLL filter in the > disciplined oscillator. The problem shows up when the GPS constellation is in a configuration that accentuates the error. That’s often a 12 / 24 / 48 hour sort of thing. Bob > > I'm no expert, especially not in math. These hints are thoughts that > come to mind. > > Bill Hawkins > > > -----Original Message----- > From: Ole Petter Ronningen > Sent: Monday, December 15, 2014 3:04 AM > > I would like to get a better idea of what my actualt antenna location > is, so that I can manually set the position in the GPSDOs. For that > purpose I set up a Ublox M8N with logging in U-center, and I've > collected about 250K readings over several days. For each reading I also > log number of SV's used, as well as HDOP, VDOP. PDOP, thinking I would > filter the list and end up with a subset of really good fixes.The idea > is then to average the "best readings" and use that as my position. > > My question is twofold; 1) is this for some reason a bad idea? And 2) > How do I average the numbers? I can not put my finger on it but it > "feels wrong" to average lat, long and height independently. > > Any hints are greatly appreciated. > > > _______________________________________________ > 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.

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GPS position averaging