| Topic: |
Science > Physics |
| User: |
"B Gilmour" |
| Date: |
07 Sep 2004 02:28:26 PM |
| Object: |
GPS ques |
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
The satellites are however in geosynchronous orbits, where I thought there
would be no relative velocities between satellite and observer, I'm aware
that there is acceleration in orbits but this is GR not SR..
Thanks
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| User: "Dirk Van de moortel" |
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| Title: Re: GPS ques |
07 Sep 2004 12:57:45 PM |
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"B Gilmour" <wgilmour@I-zoom.net> wrote in message news:2q69g8Fro3unU1@uni-berlin.de...
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
The satellites are however in geosynchronous orbits, where I thought there
would be no relative velocities between satellite and observer, I'm aware
that there is acceleration in orbits but this is GR not SR..
They are not in geosync.
You'll find an excellent introduction to the GPS and relativity
right here:
http://www.eftaylor.com/pub/projecta.pdf
but first read the two chapters:
http://www.eftaylor.com/pub/chapter1.pdf
http://www.eftaylor.com/pub/chapter2.pdf
Seriously more advanced stuff:
http://www.gfy.ku.dk/~cct/Speciale1.pdf
hth
Dirk Vdm
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| User: "Uncle Al" |
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| Title: Re: GPS ques |
07 Sep 2004 01:07:33 PM |
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B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Nature 425 374 (2003)
<http://rattler.cameron.edu/EMIS/journals/LRG/Articles/Volume6/2003-1ashby/index.html>
http://www.eftaylor.com/pub/projecta.pdf
<http://www.public.asu.edu/~rjjacob/Lecture16.pdf>
Relativity in the GPS system
http://arxiv.org/abs/gr-qc/0306076.pdf
<http://www.metaresearch.org/solar%20system/gps/absolute-gps-1meter-3.ASP>
http://www.navcen.uscg.gov/pubs/gps/gpsuser/gpsuser.pdf
http://www.navcen.uscg.gov/pubs/gps/sigspec/default.htm
http://www.navcen.uscg.gov/pubs/gps/icd200/default.htm
http://www.trimble.com/gps/index.html
http://sirius.chinalake.navy.mil/satpred/
http://www.phys.lsu.edu/mog/mog9/node9.html
http://egtphysics.net/GPS/RelGPS.htm
http://www.schriever.af.mil/gps/Current/current.oa1
http://edu-observatory.org/gps/gps_books.html
<http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html>
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "John Morriss" |
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| Title: Re: GPS ques |
07 Sep 2004 05:49:47 PM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
IMHO, anyway...
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
07 Sep 2004 10:43:43 PM |
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(John Morriss) wrote in message news:<9661bda2.0409071449.5909e703@posting.google.com>...
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
You are correct. Uncle Al goofed.
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
IMHO, anyway...
Since it is generally safe to assume that we are not breathing vacuum
or swimming through rock, the slight remaining ambiguity is generally
easy to resolve... :-)
Myxococcus xanthus
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| User: "ZZBunker" |
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| Title: Re: GPS ques |
07 Sep 2004 10:25:11 PM |
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(John Morriss) wrote in message news:<9661bda2.0409071449.5909e703@posting.google.com>...
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
There is no ambiguity, since it's all done with mirrors.
A constellation of four *properly-placed* Geo-sync satellites,
pulsing with ANY transmitter with sufficient ambiguity resolution,
it's doesn't have to be a clock, will give you
a fixed-point in *Poincare* Space, not Physical Space.
IMHO, anyway...
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| User: "Bruce Bowen" |
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| Title: Re: GPS ques |
08 Sep 2004 11:31:51 AM |
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(John Morriss) wrote in message news:<9661bda2.0409071449.5909e703@posting.google.com>...
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
Actually, for all practical purposes you do. The GPS receiver uses
a high quality quartz VCXO that is phase locked to the GPS signal.
Since the GPS signal is based on an atomic clock, so are you. Of
course you need a least one satellite to set "absolute phase". It's
similar to those "atomic clocks" you can buy at Target that sync to
the NIST time sync signal, only much more responsive and dynamic.
-Bruce
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| User: "Uncle Al" |
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| Title: Re: GPS ques |
07 Sep 2004 06:03:43 PM |
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John Morriss wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
IMHO, anyway...
The universe doesn't care about your opinion.
http://www.gpsy.com/gpsinfo/
http://www.gpsy.com/gpsinfo/gps-faq.txt
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "John Morriss" |
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| Title: Re: GPS ques |
08 Sep 2004 09:09:26 AM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413E3E4F.EAC18A72@hate.spam.net>...
John Morriss wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
IMHO, anyway...
The universe doesn't care about your opinion.
http://www.gpsy.com/gpsinfo/
http://www.gpsy.com/gpsinfo/gps-faq.txt
Thanks for the references.. The following is pasted from the second one...
If the receiver had a perfect clock, exactly in sync with those on
the satellites, three measurements, from three satellites, would
be sufficient to determine position in 3 dimensions.
Unfortunately, you can't get a perfect clock that will fit
(financially or physically) in a $300 (or even $3000) receiver, so
a fourth satellite is needed to resolve the receiver clock error.
The universe doesn't care about your opinion.
At last; a dictum with universal application...
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
08 Sep 2004 02:42:10 AM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413E3E4F.EAC18A72@hate.spam.net>...
John Morriss wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
Calfshit... :)
The above would be true if you possessed an atomic clock equal in
accuracy to the GPS clocks. Lacking such a timepiece:
1) Two satellites put you on the surface of a hyperboloir of
revolution;
2) Three satellites put you on the line of intersection of two
such Hyps of Rev
3) Four satellites put you at one of the set of points where this
line intersects the third Hyp of Rev There IS ambiguity remaining...
IMHO, anyway...
The universe doesn't care about your opinion.
Al, you made a blunder. Fess up and stop being so ***** nasty all the time.
Myxococcus xanthus
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| User: "tj Frazir" |
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| Title: Re: GPS ques |
07 Sep 2004 08:01:03 PM |
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two sigs on a scope is better than an atomic clock . wvae top to wave
top is distance at C.
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| User: "Morituri-Max" |
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| Title: Re: GPS ques |
08 Sep 2004 12:33:53 AM |
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tj Frazir wrote:
two sigs on a scope is better than an atomic clock . wvae top to wave
top is distance at C.
R I A W G
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
08 Sep 2004 08:00:08 AM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
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| User: "Uncle Al" |
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| Title: Re: GPS ques |
08 Sep 2004 12:18:39 PM |
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Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
B Gilmour wrote:
As I understand it, GPS has 2 relativistic corrections to make it accurate,
One under SR due velocity difference, the satellite clock runs slow by a
small margin,
and one under GR due gravity being less, the satellite clock runs faster by
a larger margin.
GPS is massively corrected.
The satellites are however in geosynchronous orbits,
[snip]
*****. They would be useless in geosynchronous orbit
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
08 Sep 2004 06:20:51 PM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
Sam, a little assistance here? I don't want to get into any sort of
shouting match with Al.
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Myxococcus xanthus
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| User: "Ian Stirling" |
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| Title: Re: GPS ques |
08 Sep 2004 09:43:27 PM |
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Myxococcus xanthus <mold-guardian@comcast.net> wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
Sam, a little assistance here? I don't want to get into any sort of
shouting match with Al.
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Given a consistently ticking clock, it's possible.
The clock doesn't need to be set, or tell time.
However, you need to be able to observe the sat for long enough that you
can infer your clocks rate and the absolute time from the doppler.
You of course need to be stationary for the several hours this will take,
or have a really, really good inertial navigation system.
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
09 Sep 2004 12:49:33 AM |
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"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:413fc34f$0$15100$ed2619ec@ptn-nntp-reader01.plus.net...
Myxococcus xanthus <mold-guardian@comcast.net> wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message
news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message
news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a
circle.
3) Three GPS satellites locate you at two points on a circle -
one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for
once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
Sam, a little assistance here? I don't want to get into any sort of
shouting match with Al.
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Given a consistently ticking clock, it's possible.
The clock doesn't need to be set, or tell time.
However, you need to be able to observe the sat for long enough that you
can infer your clocks rate and the absolute time from the doppler.
You of course need to be stationary for the several hours this will take,
or have a really, really good inertial navigation system.
Hmmm... an interesting suggestion. Yes, such might be possible
1) if GPS broadcast frequencies are stable enough, and
2) if you have an accurate frequency standard against which to check the
doppler-shifted frequency of the GPS broadcast.
Then it MIGHT be possible, from several hours of recording the shifting
doppler characteristics of the GPS satellite, to deduce where in the orbit
the GPS satellite is relative to you. I haven't worked out the math, but it
does seems plausible.
But I'm not quite ready to shout Touche'. The problem is,
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
2') The only accurate enough frequency standard for this exercise (assuming
that you want to deduce your distance to within several meters) would be a
cesium or rubidium reference oscillator...
:-)
Myxococcus xanthus
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
09 Sep 2004 01:03:30 AM |
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"Myxococcus xanthus" <mold-guardian_NO_SPAM@comcast.net> wrote in message
news:N9S%c.404619$%_6.220476@attbi_s01...
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
Ouch! I just realized that you could monitor the GPS timing signals, so
scratch this objection!
2') The only accurate enough frequency standard for this exercise
(assuming
that you want to deduce your distance to within several meters) would be a
cesium or rubidium reference oscillator...
But this objection still holds.
Myxococcus xanthus
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| User: "Ian Stirling" |
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| Title: Re: GPS ques |
09 Sep 2004 12:36:50 PM |
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Myxococcus xanthus <mold-guardian_NO_SPAM@comcast.net> wrote:
"Myxococcus xanthus" <mold-guardian_NO_SPAM@comcast.net> wrote in message
news:N9S%c.404619$%_6.220476@attbi_s01...
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
Ouch! I just realized that you could monitor the GPS timing signals, so
scratch this objection!
AIUI, the frequencies are locked to as great a degree as the times.
2') The only accurate enough frequency standard for this exercise
(assuming
that you want to deduce your distance to within several meters) would be a
cesium or rubidium reference oscillator...
But this objection still holds.
It does.
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| User: "tj Frazir" |
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| Title: Re: GPS ques |
09 Sep 2004 07:05:06 PM |
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2 sats beat LAT and 2 beet long.
thats 4 sats to pinpoint position.
24 sats 12 ew 12 ns will sound in the same place the last one did
,,as if they dint move..
like a wheel turning wit a strobe light on to make it look still.
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| User: "Morituri-Max" |
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| Title: Re: GPS ques |
09 Sep 2004 11:51:47 PM |
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tj Frazir wrote:
like a wheel turning wit a strobe light on to make it look still.
R I A Word Game
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
10 Sep 2004 01:27:13 PM |
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Ian Stirling <root@mauve.demon.co.uk> wrote in message news:<414094b2$0$63992$ed2619ec@ptn-nntp-reader02.plus.net>...
Myxococcus xanthus <mold-guardian_NO_SPAM@comcast.net> wrote:
"Myxococcus xanthus" <mold-guardian_NO_SPAM@comcast.net> wrote in message
news:N9S%c.404619$%_6.220476@attbi_s01...
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
AIUI, the frequencies are locked to as great a degree as the times.
I checked the Interface Control Document
http://www.navcen.uscg.gov/pubs/gps/icd200/icd200cw1234.pdf
You are correct and I was wrong.
So half a Touche'? Let's split it. I divide and you choose.
You prefer the Tou or the che' half? :-)
Myxococcus xanthus
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| User: "John C. Polasek" |
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| Title: Re: GPS ques |
09 Sep 2004 07:06:10 PM |
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On Thu, 09 Sep 2004 05:49:33 GMT, "Myxococcus xanthus"
<mold-guardian_NO_SPAM@comcast.net> wrote:
"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:413fc34f$0$15100$ed2619ec@ptn-nntp-reader01.plus.net...
Myxococcus xanthus <mold-guardian@comcast.net> wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message
news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message
news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a
circle.
3) Three GPS satellites locate you at two points on a circle -
one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for
once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
Sam, a little assistance here? I don't want to get into any sort of
shouting match with Al.
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Given a consistently ticking clock, it's possible.
The clock doesn't need to be set, or tell time.
However, you need to be able to observe the sat for long enough that you
can infer your clocks rate and the absolute time from the doppler.
You of course need to be stationary for the several hours this will take,
or have a really, really good inertial navigation system.
Hmmm... an interesting suggestion. Yes, such might be possible
1) if GPS broadcast frequencies are stable enough, and
2) if you have an accurate frequency standard against which to check the
doppler-shifted frequency of the GPS broadcast.
Then it MIGHT be possible, from several hours of recording the shifting
doppler characteristics of the GPS satellite, to deduce where in the orbit
the GPS satellite is relative to you. I haven't worked out the math, but it
does seems plausible.
But I'm not quite ready to shout Touche'. The problem is,
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
2') The only accurate enough frequency standard for this exercise (assuming
that you want to deduce your distance to within several meters) would be a
cesium or rubidium reference oscillator...
:-)
Myxococcus xanthus
You have the wrong idea entirely. For one thing the cesium frequency
cannot be changed at will. There is no Doppler effect.
What they do is send the cesium signal into a preset counter to
generate a periodic beep every second (just for argument's sake, it's
trickier than that, pseudorandom etc.).
So the compensation consists of changing the preset counter to a
higher value so the beep rate is again brought to match that on
earth. It's 38 us/day out of 8.64 x 10^10 us/day. The cesium clock is
I think about 9.19 Ghz or 9.19x10^9 hz so an increase of 4 counts
would make the 38us/day.
But don't hold me to the 9.19 Ghz (page 153 of my book Dual Space)
because 4 counts is much too crude. Someone else may have more
information. Anyway forget about broadcast frequency stability.
Mr. Dual Space
(If you have something to say, write an equation.
If you have nothing to say, write an essay).
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
10 Sep 2004 04:26:45 AM |
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John C. Polasek <jpolasek@cfl.rr.com> wrote in message news:<v4r1k01han3qskf61o379pc452uht811bh@4ax.com>...
On Thu, 09 Sep 2004 05:49:33 GMT, "Myxococcus xanthus"
<mold-guardian_NO_SPAM@comcast.net> wrote:
"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:413fc34f$0$15100$ed2619ec@ptn-nntp-reader01.plus.net...
Myxococcus xanthus <mold-guardian@comcast.net> wrote:
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Given a consistently ticking clock, it's possible.
The clock doesn't need to be set, or tell time.
However, you need to be able to observe the sat for long enough that you
can infer your clocks rate and the absolute time from the doppler.
You of course need to be stationary for the several hours this will take,
or have a really, really good inertial navigation system.
Hmmm... an interesting suggestion. Yes, such might be possible
1) if GPS broadcast frequencies are stable enough, and
2) if you have an accurate frequency standard against which to check the
doppler-shifted frequency of the GPS broadcast.
Then it MIGHT be possible, from several hours of recording the shifting
doppler characteristics of the GPS satellite, to deduce where in the orbit
the GPS satellite is relative to you. I haven't worked out the math, but it
does seems plausible.
But I'm not quite ready to shout Touche'. The problem is,
1') My guess is that the GPS broadcast frequencies are no more accurate or
stable than your standard crystal RF oscillator, and
2') The only accurate enough frequency standard for this exercise (assuming
that you want to deduce your distance to within several meters) would be a
cesium or rubidium reference oscillator...
:-)
Myxococcus xanthus
You have the wrong idea entirely. For one thing the cesium frequency
cannot be changed at will. There is no Doppler effect.
What they do is send the cesium signal into a preset counter to
generate a periodic beep every second (just for argument's sake, it's
trickier than that, pseudorandom etc.).
So the compensation consists of changing the preset counter to a
higher value so the beep rate is again brought to match that on
earth. It's 38 us/day out of 8.64 x 10^10 us/day. The cesium clock is
I think about 9.19 Ghz or 9.19x10^9 hz so an increase of 4 counts
would make the 38us/day.
But don't hold me to the 9.19 Ghz (page 153 of my book Dual Space)
because 4 counts is much too crude. Someone else may have more
information. Anyway forget about broadcast frequency stability.
Er...
If you haven't noticed, this section of the thread has moved
completely off the original topic. Your response has absolutely
NOTHING to do with what Ian and I are currently discussing. We are
discussing neither GR time dilation, nor Androcles/Wilson's alleged
source dependency effects, nor Uncle Al's blunder.
Myxococcus xanthus
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
10 Sep 2004 04:15:06 AM |
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Ian Stirling <root@mauve.demon.co.uk> wrote in message news:<413fc34f$0$15100$ed2619ec@ptn-nntp-reader01.plus.net>...
Myxococcus xanthus <mold-guardian@comcast.net> wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
Sam, a little assistance here? I don't want to get into any sort of
shouting match with Al.
Unless you are carrying some sort of Cesium reference clock along with
you, how can you determine your distance from a single GPS satellite?
Given a consistently ticking clock, it's possible.
The clock doesn't need to be set, or tell time.
However, you need to be able to observe the sat for long enough that you
can infer your clocks rate and the absolute time from the doppler.
You of course need to be stationary for the several hours this will take,
or have a really, really good inertial navigation system.
Did a little research. Your idea is not only theoretically feasible,
it is exactly how the old TRANSIT system worked!
"If the user is, in addition, stationary or has a known speed then, in
principle, the position can be obtained by the observation of a
complete pass of a SINGLE satellite. This could be called the
"transit" mode, because the old TRANSIT system uses this method. In
the case of GPS, however, the apparent motion of the satellite is much
slower, requiring much more stability of the user clock."
http://tycho.usno.navy.mil/gpsinfo.html
"Transit was the first operational satellite navigation system.
Developed by the Johns Hopkins Applied Physics Laboratory, the system
was intended as an aid to submarine navigation.
The Transit system allowed the user to determine position by measuring
the doppler shift of a radio signal transmitted by the satellite. The
user was able to calculate position to within a few hundred meters as
long as the user knew his altitude and the satellite ephemeris."
http://ares.redsword.com/GPS/old/sum_pre.htm#transit
Myxococcus xanthus
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| User: "tj Frazir" |
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| Title: Re: GPS ques |
10 Sep 2004 10:08:25 AM |
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john Hopkins wrote what we wnted rusians to think.
No on wants anyone to know how simple it is.
its as simple as looking at the sound on a scope from a drumb at each
end of the football field. As long as boath sounds from the drumbs
cross the goal post at the same time your only mic hears them boath
and you see the peak of each drumb on the scope .
The distance from peaks is time and the time is converted to distance.
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| User: "Morituri-Max" |
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| Title: Re: GPS ques |
10 Sep 2004 11:31:23 AM |
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tj Frazir wrote:
its as simple as looking at the sound on a scope from a drumb at each
R i A W G
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| User: "tj Frazir" |
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| Title: Re: GPS ques |
09 Sep 2004 06:59:21 PM |
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the sats nead clocks ,,two sats per direction.
The reciver dont nead a clock .
All the reciver must do is listen with an entena and put it on the
scope . Then mesure the distance between wave tops as it looks at 2
sigs from 2 sats on top each other .
There is no time dialation .
The only time ajusted is on when each sat sends the sig so the sig
passes the goal post from boath sats at the same time.
Your in the field and a drum beats at each end of the field at the goal
post at the same time .
you mesure the time between beets and convert it to distance.
IF one drumb moves back away from the post the time that drumb beets
neads corected so the sound is at the post when the sound is at the
other post so they cross the post at the same time.
There is no other time corections in gps.
My sigless GPS puts your GPS to shame.
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| User: "Morituri-Max" |
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| Title: Re: GPS ques |
09 Sep 2004 11:52:19 PM |
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tj Frazir wrote:
There is no time dialation .
My sigless GPS puts your GPS to shame.
R I A W G (twice)
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| User: "Myxococcus xanthus" |
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| Title: Re: GPS ques |
10 Sep 2004 05:35:39 AM |
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Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
Myxococcus xanthus wrote:
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413DF8E5.BD8368CE@hate.spam.net>...
1) One GPS satellite puts you on the surface of a sphere.
2) Two GPS satellites intersect two spheres - puts you on a circle.
3) Three GPS satellites locate you at two points on a circle - one
of which is trivially wrong.
4) Four GPS satellites define a unique point in 3-space.
You've made this same blunder before...almost TWO YEARS ago. See:
http://groups.google.com/groups?selm=3DE4ECAF.F95D317A%40hate.spam.net
You accuse others of being stoopid. Try learning some humility, for once.
Myxococcus xanthus
You are wrong. Talk with GPS vendors.
You haven't answered me yet. Leaving aside the interesting point that
Ian made (that in real life, a single GPS satellite would exhibit
Doppler effects that could be used for determining position, the way
satellites in the old TRANSIT system were monitored), let me present
you with the following scenario:
An atomic clock controls a huge billboard display exhibiting the
following:
Latitude: 34 degrees 5 minutes 29.3504 seconds North
Longitude: 118 degrees 22 minutes 16.4312 seconds West
Date/Time: September 10, 2004 / 05:24:13.0143451222
You are observing the sign with a large telescope from far away. In
your hand is a quartz watch that has not been set particularly
accurately.
You stated, "One GPS satellite puts you on the surface of a sphere."
OK, that implies that there is enough information in the scenario I
presented to determine your distance from the billboard.
Show me the calculations, Al. Or admit your mistake.
Making mistakes isn't the end of the world, Al. I've made several in
this thread as well as in the GPS versus source dependency thread.
Being able to admit mistakes is one of the factors distinguishing
legitimate contributors in these newsgroups from crackpots.
Myxococcus xanthus
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| User: "robert egri" |
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| Title: Re: GPS ques |
10 Sep 2004 10:14:46 AM |
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(Myxococcus xanthus) wrote in message news:<ce5e7813.0409100235.478fe5f4@posting.google.com>...
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<413F3EEF.4DEBBD50@hate.spam.net>...
[...]
Show me the calculations, Al. Or admit your mistake.
Making mistakes isn't the end of the world, Al. I've made several in
this thread as well as in the GPS versus source dependency thread.
Being able to admit mistakes is one of the factors distinguishing
legitimate contributors in these newsgroups from crackpots.
Myxococcus xanthus
Instead of telling UA to admit his "mistakes", open a book and learn
about phase locked loops.
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