prototyping GPS
RichD
on earth... which invites the question: how was it originally tested
and calibrated? I mean, you throw those satellites up there,
power on, get some data... but how do you evaluate the data?
GIGO is reality, and we must pay homage to the great god Murphy...
I'm looking at it as an engineering problem - how was the system
debugged, calibrated, and how do they do ongoing verification?
--
Rich
Sam Wormley
> GPS is now the reference for measuring distance and location
> on earth...
GPS provides Postition, Velocity and Time (PVT)
http://edu-observatory.org/gps/gps_books.html
which invites the question: how was it originally tested
> and calibrated? I mean, you throw those satellites up there,
> power on, get some data... but how do you evaluate the data?
> GIGO is reality, and we must pay homage to the great god Murphy...
The figure of the earth for gps is modeled by WGS-84 datum.
http://en.wikipedia.org/wiki/WGS84
>
>
> I'm looking at it as an engineering problem - how was the system
> debugged, calibrated, and how do they do ongoing verification?
http://edu-observatory.org/gps/status.html
Some Measurements of Accurac
Y.Porat
----------------
and more abstractly talking
it was done by **trial and error!!**
as most practival science and technology
is done !!
while the precision is a result of that
long process
of trial and error
GPS is too heavily dependant
on too may factors
to be 'predicted' precisely -by any theory
ATB
Y.Porat
------------------------
bule...@columbus.rr.com
The information you want is readily available for a high level of
understandingexcruciatingly difficult to understand the details.
I believe that the accuraccy ( the constant updating of the ephemerus
data) is gathered from constant measurements made by 5 stattions setup
around the world. These stations are in Colorodo, Hawaii, Ascension
Islands, Diego Garcia and Kawajalein. The coordination of all the data
is done in Colorado.
o...@uakron.edu
reflectors and ground based lasers were used to map out orbits
relative to WGS-84, as well as other means.
Steve
Jerry
Details on the developmental history of GPS are extremely scanty
on the internet, but it appears that design work began in 1973.
In 1978 the DoD sent up the first of several engineering
prototypes, at first to establish proof-of-concept, then to test
the evolving hardware/software designs and finally integration
test of partial and then complete systems.
Jerry
Y.Porat
--------------
so as i said
a trial and error system
nothing to do with the crooks
(or suckers )of GR!!
Y.Porat
-------------------
John Larkin
There were prototypes:
http://en.wikipedia.org/wiki/NAVSAT
I used to sell time on a PDP-8 to Offshore Navigation Inc, to analyze
Transit data... paper tape in and out, hardly realtime navigation. I
also cobbled together a custom version of the FOCAL language, for the
PDP-11, to do satnav calcs for another outfit. Both were sort of test
applications, before the GPS constellation was launched. A lot of
people were interested early-on.
ONI used the Raydist (Loran-like) and SHORAN (uhf pulsed thing)
systems for navigation to drilling rigs and well heads in the Gulf of
Mexico. Their service was expensive, and included an operator with
every system. I bet GPS sure whacked them. Luckily, they had another
division, OHI, Offshore Helicopters Inc.
I think there are still a few LORAN nets working.
John
hhc...@yahoo.com
Rich, thanks for posting one of the more thought provoking question
that I've read in recent years on sci.physics.
As Sam has pointed out, I believe that GPS relies rather heavily on
WGS-84 datum, which also is the datum used on the current generation
of navigational charts in use, and the delineation of state, national,
and international boundaries. Lat-Lon reference points or benchmarks
exist at a number of major observatories both in the US and
distributed througout the globe.
The calibration basis for WGS-84 is interesting in itself, and is
based upon an update of WGS-60 data supplied using very high precision
surveying methodology that replaced the use of physical survey chain
measurement with electronic chains. (This was prior to the
availability of laser based survey equipment.)
Some of us are old enough to remember seeing being done in the areas
where we lived, although the purpose (other than to precisely fix
international borders) was somewhat murky. I remember that it
involved building a number of large, steel, towers that were later
removed and relocated elsewhere. I have no idea how the measurements
were made, but they either employed optical or electronic means. What
later was revealed to the public related only to a comparision to the
Lewis and Clark survey and how amazingly accurate the Lewis and Clark
datum was, their benchmarks often being off only by a few yards, or in
some cases only a few feet!
Your question is also interesting for a totally different reason, and
it points to the fact that you are likely either an engineer, physical
scientist, or a student in the field. You evidently realize the
difference between "precision" an "accuracy", while very few laymen
do. No one doubts that GPS is capable of a great deal of accuracy,
and can deliver location coordinates to almost any called for number
of decimal places. It is a system capable of great precision, and most
people understand this. What you are questioning is it "accuracy",
and how that accuracy is obtained.
With GPS, accuracy is determine largely based upon the primary
reference benchmarks, and is therefore has a maximum accuracy that can
be no greater than the positional accuracy the benchmarks upon which
it is based or calibrated. All GPS locations, other than at the
refence benchmarks, are determined interpolation, hence can be very
precise, yet still slightly inaccurate. The question becomes, how
inaccurate is GPS; how is this inaccuracy quantified; and how is the
accuracy improved?
Harry C.
hhc...@yahoo.com
Whoops, that post contained some wording that can lead readers a very
incorrect picture of the GPS system.
It should be pointed out that. in essence, GPS satellites transmit
only timing information with which your GPS reader determines your
your position on earth, latitude, longitude, and elevation. GPS
satellites transmit no cartography data at all. only very accurate and
precise time checks. Based on a reception of the timing information
received from multiple GPS satellites, it computes its position on
earth, and processes all of the corrrections, interpolations, or user
inputs that it has been programmed from its manufacturer to perform.
Rember that GPS is a collective term for the entire system, which
includes a constellation of orbital satellites that provide timing
data, and your reciever which performs all location computations.
This raises still another potentially interesting question. How and
from where do GPS receiver manufacturers obtain their software
algorithms?
Is there a softare design document distributed by the government?
Does Garmin or Magellin market this information, and if so, where and
how did they get it? Is it a product of US government funded R&D, and
because of this in the public domain?
Harry C.
Tim Wescott
With expensive enough instruments you can pinpoint where the satellite
is, you should know just how much time it'll take for its signal to get
to you, and how precise its clock is.
From this, you can work out whether it's working within spec on a
satellite-by-satellite basis.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
linnix
> This raises still another potentially interesting question. How and
> from where do GPS receiver manufacturers obtain their software
> algorithms?
The idea is simple. You decode phase-shifted timing data from three
to four geosynchronized satellites (known locations). Any good second
year engineering student can do it. The difficult part is building
low power and low cost components.
> Is it a product of US government funded R&D, and
> because of this in the public domain?
Yes.
Joel Koltner
news:6e0d7409-3ddd-45d1...@m44g2000hsc.googlegroups.com...
"This raises still another potentially interesting question. How and
from where do GPS receiver manufacturers obtain their software
algorithms?"
These days, I imagine they just check out one of the many books on the topic
from Amazon. :-) (I expect something like this;
http://www.amazon.com/Software-Defined-GPS-Galileo-Receiver-Single-Frequency/dp/0817643907
... probably has lots of good references in it... this upcoming release also
looks potentially fruitful:
http://www.amazon.com/GPS-Software-Library-Guochang-Xu/dp/3540766200). Early
on, it does seem to have flowed from the government to the big defense
contractors. It'd be interesting to see when GPS first "made the jump" to the
industrial market and whether the first companies marketing GPS receivers as
such were formed out of former defense contractor or government employees vs.
just having some really clever people on-board who could put enough together
from the various academic papers published on the system and whatever they
could get out of the government to build a working prototype.
Note that these days a lot of the "consumer" GPS receivers by Garmin and
Magellan use off-the-shelf GPS modules containing chipsets from, e.g., SiRF
Technology, Atmel, etc.
---Joel
Falk Willberg
> <hhc...@yahoo.com> wrote in message
> news:6e0d7409-3ddd-45d1...@m44g2000hsc.googlegroups.com...
> "This raises still another potentially interesting question. How and
> from where do GPS receiver manufacturers obtain their software
> algorithms?"
>
> These days, I imagine they just check out one of the many books on the topic
> from Amazon. :-)
Or download ICD 200: http://206.65.196.29/pubs/gps/icd200/ICD200Cw1234.pdf
Falk
--
Dax 4.784 -1,0% Dow 9.022 -2,6% N225 9.306 +0,0%
Dave
> It should be pointed out that. in essence, GPS satellites transmit
> only timing information with which your GPS reader determines your
> your position on earth, latitude, longitude, and elevation. GPS
> satellites transmit no cartography data at all. only very accurate and
> precise time checks.
This is incorrect. GPS satellites transmit both the time and the
location of the satellite.
Dave
zzbu...@netscape.net
Well, that's the problem with GPS though. When you transmit
both the "time" and "location" from GPS, you are MAXIMALLY
redundant in the information theory sense.
Which is why Cruise Missiles, AAVs, AUVs, AHVs, AVVs,
HDTV[], Post Ford Batteries, Post AT&T Fiber Optics, RISC++,
Post GM Robotics, XML, and USB work so well in sinking submarines.
>
> Dave
Richard Henry
> RichD wrote:
> > GPS is now the reference for measuring distance and location
> > on earth... which invites the question: how was it originally tested
> > and calibrated? I mean, you throw those satellites up there,
> > power on, get some data... but how do you evaluate the data?
> > GIGO is reality, and we must pay homage to the great god Murphy...
>
> > I'm looking at it as an engineering problem - how was the system
> > debugged, calibrated, and how do they do ongoing verification?
>
> > --
> > Rich
>
> With expensive enough instruments you can pinpoint where the satellite
> is, you should know just how much time it'll take for its signal to get
> to you, and how precise its clock is.
>
> From this, you can work out whether it's working within spec on a
> satellite-by-satellite basis.
>
> --
>
> Tim Wescott
>
> Do you need to implement control loops in software?
> "Applied Control Theory for Embedded Systems" gives you just what it says.
> See details athttp://www.wescottdesign.com/actfes/actfes.html
The US Navy Observatory freequently sends calibration signals to the
satellites to keep the system operating in spec.
They also check the prevailing attitude on sci.physics to see whether
or not to apply the relativistic corrections.
john jardine
"Richard Henry" <pome...@hotmail.com> wrote in message
news:6689da64-d90e-47c9...@a19g2000pra.googlegroups.com...
[...]
They also check the prevailing attitude on sci.physics to see whether
or not to apply the relativistic corrections.
Love it!. Just my thing. First time today I've laughed out loud.
Androcles
"Richard Henry" <pome...@hotmail.com> wrote in message
news:6689da64-d90e-47c9...@a19g2000pra.googlegroups.com...
=========================================
Hahaha!
And since the heart of the system is in the receiver, absolutely and
totally independent of the US Naval Observatory, Tom-Tom and
Garmin also check with sci.physics.relativity on how to design
the software in their product -- just in case the clock is 38
nanoseconds off local time. Apparently being an hour off when
we set the clocks back at the end of daylight savings time places
us somewhere near the orbit of Saturn.
Androcles
"john jardine" <john.j...@idnet.co.uk> wrote in message
news:00be4635$0$10791$c3e...@news.astraweb.com...
David Bernier
I'm upgrading on GR from Buy to: Market outperform.
hanson
news:00be4635$0$10791$c3e...@news.astraweb.com...
>
news:6689da64-d90e-47c9...@a19g2000pra.googlegroups.com...
[...]
They also check the prevailing attitude on sci.physics
to see whether or not to apply the relativistic corrections.
>
Love it!. Just my thing. First time today I've laughed out loud.
>
... ahahaha... Uncle Henry has truly class. He once insisted
that TV factories hire "relativity scientists"... ... ahaha...
>
And to uncle Henry's further credit it must be stated that
he once posted that he is an "Almost-victim"... up in his
pomerado backyard in the San Jacinto Range...
Maybe it's from his apple cider or maybe he slipped
on an apple peel that turned him into an "Almost-victim"...
>
What can I tell you, except, thanks for the laughs!...
AHAHAHAHA... ahhahaha... ahahahanson:
>
PS:
Here's more like this on that REL-GPS... ahahaha...:
http://tinyurl.com/6frczv ---- or ----
http://groups.google.com/group/sci.physics/msg/e82082d7ed163bd2?hl=en
hhc...@yahoo.com
Actually, I doubt if one of my second year engineering students could
even absorb the problem parameters as you appear to do.
Realize that the GPS receive has absolutely no knowledge of the
satellites orbital positions nor do the satellites themselves. GPS
receivers, on the other hand have not idea of the directional
information on the signals that they are receiving, and typically must
receive signal from three satellites simultaneously.
Since to you "The idea is simple" so explain the basics of the
algorithm that you would use to "decode phase-shifted timing data from
three
to four geosynchronized satellites (known locations)" Slight problem
genius, neither the satellites nor the GPS receiver knows its current
location. So, I receive (my microwave reciever guys are very gifted)
a number of timing signals from a source that may or my not identify
itself, and has not concept of its current orbital location.
So genius, what is the first, second and third step to identify the
GPS receiver's position on earth?
It's a remarkably interesting question, for which you haven't the hint
of a clue, Dork.
Next...
Harry C.
hhc...@yahoo.com
wrote:
> <hhc...@yahoo.com> wrote in message
>
> news:6e0d7409-3ddd-45d1...@m44g2000hsc.googlegroups.com...
> "This raises still another potentially interesting question. How and
> from where do GPS receiver manufacturers obtain their software
> algorithms?"
>
> These days, I imagine they just check out one of the many books on the topic
> ... probably has lots of good references in it... this upcoming release also
> looks potentially fruitful:http://www.amazon.com/GPS-Software-Library-Guochang-Xu/dp/3540766200). Early
> on, it does seem to have flowed from the government to the big defense
> contractors. It'd be interesting to see when GPS first "made the jump" to the
> industrial market and whether the first companies marketing GPS receivers as
> such were formed out of former defense contractor or government employees vs.
> just having some really clever people on-board who could put enough together
> from the various academic papers published on the system and whatever they
> could get out of the government to build a working prototype.
>
> Note that these days a lot of the "consumer" GPS receivers by Garmin and
> Magellan use off-the-shelf GPS modules containing chipsets from, e.g., SiRF
> Technology, Atmel, etc.
>
> ---Joel
Joel, thanks, but I'm aware of that. My question is were I to make a
GPS receive or produce a module containing a chipset, what is the
source or the specifications that will allow me to design software
providing earth location coordinates.
To be perfectly honest with you, this is sort of an academic excercise
on my part, simply to keep my mind sharp and share this information
with others. I have no ambitons or profit motivations to produce a GPS
device.
So my basic assumptions are, I have associate that can build a
broadband omni directional receiver capable of receiving signals from
"n" satellies in the GPS constellation.
Let's assume that I have near infininite sofware skill, what is the
design basis for my software to determine my location on earth?
It seems like a very simple question, but I am having touble obtaining
an answer to this simple question.
Harry C.
hhc...@yahoo.com
wrote:
Wow Falk, that is a keeper that appears to answer my questions, but
will take me a week or more to fully digest.
Trust me, it's already been stored to disk.
I won't even ask how you knew of this document. That would be rude.
Thank you so much.
Harry C.
p.s., While there is a high level of noise on sci.pysics, valuable
information often apperars above the noise level, often when you least
expect it.
Hal Murray
>Joel, thanks, but I'm aware of that. My question is were I to make a
>GPS receive or produce a module containing a chipset, what is the
>source or the specifications that will allow me to design software
>providing earth location coordinates.
I don't know where to find them. Have you tried google?
>To be perfectly honest with you, this is sort of an academic excercise
>on my part, simply to keep my mind sharp and share this information
>with others. I have no ambitons or profit motivations to produce a GPS
>device.
>
>So my basic assumptions are, I have associate that can build a
>broadband omni directional receiver capable of receiving signals from
>"n" satellies in the GPS constellation.
>
>Let's assume that I have near infininite sofware skill, what is the
>design basis for my software to determine my location on earth?
>
>It seems like a very simple question, but I am having touble obtaining
>an answer to this simple question.
Lots of handwaving here.
It's a DSP problem. I'm assuming there is an A/D on the front end.
The big picture is that you need 4 satellites to solve 4 unknowns:
lat, long, elevation, and time. You also get the doppler
corrections. You can fake it with 3 satellites by assuming the
elevation is 0. (2D mode vs 3D.)
The signals are very low bandwidth. The GPS satellites transmit
(slowly) the description of their orbits. There is a chicken/egg
problem. You have to find the signal from a satellite before you
know where it is, And you need to know where it is and where you
are in order to compute the doppler corrections.
ephemeris is the buzzword to feed to google.
I'm pretty sure the first step uses a lot of trial and error.
That's why it takes (much) longer.
If you have good estimates of where you are and the time and
a recent ephemeris, then the DSP magic works much quicker.
--
These are my opinions, not necessarily my employer's. I hate spam.
hhc...@yahoo.com
Dave, how do you suppose that the satellite determines its own
position in orbit?
If you know, please expain it to me next week. Until then I will be
trying to understand the contents of that link that link that
Dr.Willberg posted.
Harry C.
Hal Murray
>Dave, how do you suppose that the satellite determines its own
>position in orbit?
They are uploaded from ground control stations.
Each satellite knows not only its own orbit, but the orbits
of the other satellites too.
Falk Willberg
> On Oct 21, 4:10 pm, Falk Willberg <Faweglasse...@falk-willberg.de>
> wrote:
>> Joel Koltner schrieb:
>>
>>> <hhc...@yahoo.com> wrote in message
>>> news:6e0d7409-3ddd-45d1...@m44g2000hsc.googlegroups.com...
>>> "This raises still another potentially interesting question. How and
>>> from where do GPS receiver manufacturers obtain their software
>>> algorithms?"
>>> These days, I imagine they just check out one of the many books on the topic
>>> from Amazon. :-)
>> Or download ICD 200:http://206.65.196.29/pubs/gps/icd200/ICD200Cw1234.pdf
> Wow Falk, that is a keeper that appears to answer my questions, but
> will take me a week or more to fully digest.
Have fun *g*
> Trust me, it's already been stored to disk.
If this is useful for you, you may want to have a look at the programs
here: http://vase.essex.ac.uk/projects/gps/djjweb/gps/gpscode/
They calculate your position from the information you can receive from
the data streams.
> I won't even ask how you knew of this document. That would be rude.
I was involved in an A-GPS project. Cold start within 5 seconds.
Falk
--
Dax 4.784 +0,0% Dow 9.034 -2,5% N225 8.675 -6,8%
donald
>> Dave, how do you suppose that the satellite determines its own
>> position in orbit?
>
> They are uploaded from ground control stations.
>
> Each satellite knows not only its own orbit, but the orbits
> of the other satellites too.
>
http://www.en.articlesgratuits.com/global-positioning-system-gps-id1210.php
Satellite transmits Ephemeris and Almanac Data to GPS receivers.
Ephemeris data contains important information about status of satellite
(healthy or unhealthy), current date and time. This part of signal is
essential for determining a position. Almanac data tells GPS receiver
where each GPS satellite should be at any time throughout the day. Each
satellite transmits almanac data showing orbital information for that
satellite and for every other satellite in the system.
Dave
[snip]
> Realize that the GPS receive has absolutely no knowledge of the
> satellites orbital positions nor do the satellites themselves.
> Slight problem
> genius, neither the satellites nor the GPS receiver knows its current
> location.
These statements are patently false. Each satellite continually
transmits messages containing the time the message was sent, a precise
orbit for the satellite sending the message (the ephemeris), and rough
orbits of all GPS satellites (the almanac).
The flight paths of the satellites are tracked by US Air Force
monitoring stations in Hawaii, Kwajalein, Ascension Island, Diego
Garcia, and Colorado Springs, along with monitor stations operated by
the National Geospatial-Intelligence Agency. The tracking information
is sent to the Air Force Space Command's master control station at
Schriever Air Force Base in Colorado Springs, which contacts each GPS
satellite regularly with a navigational update. These updates
synchronize the atomic clocks on board the satellites to within a few
nanoseconds of each other, and adjust the ephemeris of each
satellite's internal orbital model.
Dave
doug
hhc...@yahoo.com wrote:
> On Oct 21, 1:59 pm, linnix <m...@linnix.info-for.us> wrote:
>
>>>This raises still another potentially interesting question. How and
>>>from where do GPS receiver manufacturers obtain their software
>>>algorithms?
>>
>>The idea is simple. You decode phase-shifted timing data from three
>>to four geosynchronized satellites (known locations). Any good second
>>year engineering student can do it. The difficult part is building
>>low power and low cost components.
>>
>>
>>>Is it a product of US government funded R&D, and
>>>because of this in the public domain?
>>
>>Yes.
>
I think you are trying to make this much harder than it is.
I do radar imaging and the process is the same.
>
> Actually, I doubt if one of my second year engineering students could
> even absorb the problem parameters as you appear to do.
We have had undergraduates working with the location algorithms.
>
> Realize that the GPS receive has absolutely no knowledge of the
> satellites orbital positions nor do the satellites themselves.
The receivers have to have the position of the satellites or it
will not work. Part of the data stream is the orbital parameters.
That is why some GPSs will give you a sky map of the satellites.
As soon as you know the position and time from the satellites, it
is a simple geometry problem to determine your position. If you
know the distances from one satellite, you are located to the
surface of a sphere. If you know the distance from two satellites,
the intersection of the two spheres makes a circle. If you add a
third satellite, the intersection of this circle and the new
sphere gives you two points. This is why you can get a location
with three satellites if you assume you are on the surface of
the earth. With a fourth satellite, you remove the ambiguity
of the two points and have a 3d solution. The atmospheric
corrections are details that have to be added.
GPS
> receivers, on the other hand have not idea of the directional
> information on the signals that they are receiving, and typically must
> receive signal from three satellites simultaneously.
>
> Since to you "The idea is simple" so explain the basics of the
> algorithm that you would use to "decode phase-shifted timing data from
> three
> to four geosynchronized satellites (known locations)" Slight problem
> genius, neither the satellites nor the GPS receiver knows its current
> location. So, I receive (my microwave reciever guys are very gifted)
> a number of timing signals from a source that may or my not identify
> itself, and has not concept of its current orbital location.
>
> So genius, what is the first, second and third step to identify the
> GPS receiver's position on earth?
See above.
Richard Henry
> "john jardine" <john.jard...@idnet.co.uk> wrote in message
>
> news:00be4635$0$10791$c3e...@news.astraweb.com...
>
> "Richard Henry" <pomer...@hotmail.com> wrote in message
>
> news:6689da64-d90e-47c9...@a19g2000pra.googlegroups.com...
> [...]
> They also check the prevailing attitude on sci.physics
> to see whether or not to apply the relativistic corrections.
>
> "john jardine" wrote:
>
> Love it!. Just my thing. First time today I've laughed out loud.
>
> hanson wrote:
>
> ... ahahaha... Uncle Henry has truly class. He once insisted
> that TV factories hire "relativity scientists"... ... ahaha...
>
> And to uncle Henry's further credit it must be stated that
> he once posted that he is an "Almost-victim"... up in his
> pomerado backyard in the San Jacinto Range...
> Maybe it's from his apple cider or maybe he slipped
> on an apple peel that turned him into an "Almost-victim"...
>
> What can I tell you, except, thanks for the laughs!...
> AHAHAHAHA... ahhahaha... ahahahanson:
I was truly a victim a year ago this week. The 2007 fire burned down
to the same fenceline as in 2003, 1/4 mile east of the house. This
time, however, the power was out for four days so I lost everything in
the freezer that I didn't cook the first day.
hanson
"Richard Henry" <pome...@hotmail.com> wrote
On Oct 21, 8:12 pm, "hanson" <han...@quick.net> wrote:
> "john jardine" <john.jard...@idnet.co.uk> wrote in message
They also check the prevailing attitude on sci.physics
to see whether or not to apply the relativistic corrections.
>
"john jardine" wrote:
Love it!. Just my thing. First time today I've laughed out loud.
>
hanson wrote:
... ahahaha... Uncle Henry has truly class. He once insisted
that TV factories hire "relativity scientists"... ... ahaha...
>
And to uncle Henry's further credit it must be stated that
he once posted that he is an "Almost-victim"... up in his
pomerado backyard in the San Jacinto Range...
Maybe it's from his apple cider or maybe he slipped
on an apple peel that turned him into an "Almost-victim"...
>
What can I tell you, except, thanks for the laughs!...
AHAHAHAHA... ahhahaha... ahahahanson:
>
I was truly a victim a year ago this week. The 2007 fire
burned down to the same fenceline as in 2003,
1/4 mile east of the house. This time, however, the
power was out for four days so I lost everything in
the freezer that I didn't cook the first day.
>
.. Stop crying now, uncle Henry. That was a year ago
and you are back alive and well as ever... ahaha..
Besides, your insurance gigs probably increased
your net value anyway. So why begrudge the loss
of a few lbs of hamburger meat and hotdogs...
Ascribes your loss and gain ratio to "gamma" a
relativistic ratio. It should take care of all your worries.
Good talking to you, Richie... ahahaha... ahahanson
Hal Murray
http://www.u-blox.com/customersupport/docs/GPS_Compendium(GPS-X-02007).pdf
RichD
> The US Navy Observatory freequently sends
> calibration signals to the
> satellites to keep the system operating in spec.
>
> They also check the prevailing attitude on
> sci.physics to see whether
> or not to apply the relativistic corrections.
WIthout Androcles, billions around the world
would be lost... let us now observe a moment
of silence, in memory of the tragic Fikowi tribe...
--
Rich
Jujitsu Lizard
news:2293f183-caa7-421b...@m32g2000hsf.googlegroups.com...
> GPS is now the reference for measuring distance and location
> on earth... which invites the question: how was it originally tested
> and calibrated? I mean, you throw those satellites up there,
> power on, get some data... but how do you evaluate the data?
> GIGO is reality, and we must pay homage to the great god Murphy...
>
>
> I'm looking at it as an engineering problem - how was the system
> debugged, calibrated, and how do they do ongoing verification?
The other thing you should understand is that for certain systems, a ground
receiver at a known location is used to cancel out errors that are common to
both the ground-based receiver and any receivers nearby.
For example, it is my understanding that for GPS-based aircraft instrument
landing systems, you have 1 or 2 receivers on the ground at known locations
on the airfield. They essentially relay their GPS data to the aircraft via
a separate communication channel. The ILS system on the aircraft then has
available its GPS data plus information about the GPS data received by the
receiver(s) at a known position on the ground. This allows it to null out
errors (which are presumably common to both the ground receivers and the
aircraft, as they are within a few miles of each other).
For an aircraft flying an ILS approach, the ground is the really, really,
really important point of reference. I've heard it rumored that contact
with the ground by an aircraft in an unintended way or at an unintended time
or place can really be bad for airplanes and passengers. Just a rumor I've
heard.
Androcles
"Jujitsu Lizard" <jujitsu...@gmail.com> wrote in message
news:tYudnRdkrN9yRZ7U...@giganews.com...
Indeed. And the GPS vertical error bound is +/-90 feet, greater than the
horizontal. Landing 90 feet below the runway has been known to cause
fallen arches, to say nothing of sideswiping the VASIs. Landing 90 feet
above the runway is permissible although most pilots treat it as a
touch n' go.
ji...@specsol.spam.sux.com
> "RichD" <r_dela...@yahoo.com> wrote in message
> news:2293f183-caa7-421b...@m32g2000hsf.googlegroups.com...
>> GPS is now the reference for measuring distance and location
>> on earth... which invites the question: how was it originally tested
>> and calibrated? I mean, you throw those satellites up there,
>> power on, get some data... but how do you evaluate the data?
>> GIGO is reality, and we must pay homage to the great god Murphy...
>>
>>
>> I'm looking at it as an engineering problem - how was the system
>> debugged, calibrated, and how do they do ongoing verification?
>
> The other thing you should understand is that for certain systems, a ground
> receiver at a known location is used to cancel out errors that are common to
> both the ground-based receiver and any receivers nearby.
>
> For example, it is my understanding that for GPS-based aircraft instrument
> landing systems, you have 1 or 2 receivers on the ground at known locations
> on the airfield. They essentially relay their GPS data to the aircraft via
> a separate communication channel. The ILS system on the aircraft then has
> available its GPS data plus information about the GPS data received by the
> receiver(s) at a known position on the ground. This allows it to null out
> errors (which are presumably common to both the ground receivers and the
> aircraft, as they are within a few miles of each other).
Not quite, here's how the aviation system actually works.
http://www8.garmin.com/aboutGPS/waas.html
A bunch more details at:
http://en.wikipedia.org/wiki/Wide_Area_Augmentation_System
--
Jim Pennino
Remove .spam.sux to reply.
JosephKK
<m...@linnix.info-for.us> wrote:
>
>> This raises still another potentially interesting question. How and
>> from where do GPS receiver manufacturers obtain their software
>> algorithms?
Standard math.
>
>The idea is simple. You decode phase-shifted timing data from three
>to four geosynchronized satellites (known locations).
The GPS satellites are NOT geosynchronous, they are at about 10,000 km
above earth with about a 12 hour orbit. And there are about 24 of
them, with at least 6 visible at any time at any place (below 80
degrees latitude).
JosephKK
>On Oct 21, 1:59 pm, linnix <m...@linnix.info-for.us> wrote:
>> > This raises still another potentially interesting question. How and
>> > from where do GPS receiver manufacturers obtain their software
>> > algorithms?
>>
>> The idea is simple. You decode phase-shifted timing data from three
>> to four geosynchronized satellites (known locations). Any good second
>> year engineering student can do it. The difficult part is building
>> low power and low cost components.
>>
>> > Is it a product of US government funded R&D, and
>> > because of this in the public domain?
>>
>> Yes.
>
>Actually, I doubt if one of my second year engineering students could
>even absorb the problem parameters as you appear to do.
>
>Realize that the GPS receive has absolutely no knowledge of the
>satellites orbital positions nor do the satellites themselves.
Incorrect. Not only do the receivers have explicit empherides encoded
in rom, the satellites also transmit real time corrections of their
orbital data.
>GPS
>receivers, on the other hand have not idea of the directional
>information on the signals that they are receiving, and typically must
>receive signal from three satellites simultaneously.
>
>Since to you "The idea is simple" so explain the basics of the
>algorithm that you would use to "decode phase-shifted timing data from
>three
>to four geosynchronized satellites (known locations)" Slight problem
>genius, neither the satellites nor the GPS receiver knows its current
>location.
See above about updating orbital values.
>So, I receive (my microwave reciever guys are very gifted)
>a number of timing signals from a source that may or my not identify
>itself, and has not concept of its current orbital location.
>
>So genius, what is the first, second and third step to identify the
>GPS receiver's position on earth?
>
>It's a remarkably interesting question, for which you haven't the hint
>of a clue, Dork.
>
>Next...
>
>Harry C.
Damn, i wish i had not lent out that book (i never got it back). If
i had the ISBN i would point to it.
JosephKK
You do not need broadband antennas. The signals of interest are
around 1.2 GHz and 1.5 GHz. The trick is to disentangle several
signals at the same time. CDMA is the method selected by the original
authors. See "Gold codes" named after professor Gold.
JosephKK
hal-u...@ip-64-139-1-69.sjc.megapath.net (Hal Murray) wrote:
> http://www.u-blox.com/customersupport/docs/GPS_Compendium(GPS-X-02007).pdf
Did you really think it is right to inflict us with advertising?
JosephKK
<john.j...@idnet.co.uk> wrote:
>
>"Richard Henry" <pome...@hotmail.com> wrote in message
>news:6689da64-d90e-47c9...@a19g2000pra.googlegroups.com...
>[...]
>
>They also check the prevailing attitude on sci.physics to see whether
>or not to apply the relativistic corrections.
>
>Love it!. Just my thing. First time today I've laughed out loud.
>
Crickey, you are easy to entertain.
JosephKK
How did you manage to fuck up the settings in outhouse express to ruin
your quoting soo badly.
JosephKK
You should have not bothered with the garmin page. It has too many
false items. Good differential GPS is 1 cm or better resolution, not
really quite good enough for surveying, but still used that way.