prototyping GPS

"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:

PS: Here's more like this on that REL-GPS... ahahaha...:

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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.

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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.

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topic

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.

I don't know where to find them. Have you tried google?

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.

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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.

They are uploaded from ground control stations.

Each satellite knows not only its own orbit, but the orbits of the other satellites too.

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These are my opinions, not necessarily my employer\'s.  I hate spam.

snipped-for-privacy@yahoo.com schrieb:

Have fun *g*

If this is useful for you, you may want to have a look at the programs here:

They calculate your position from the information you can receive from the data streams.

I was involved in an A-GPS project. Cold start within 5 seconds.

Falk

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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.

On Oct 22, 12:51=A0am, " snipped-for-privacy@yahoo.com" wrote: [snip]

[snip]

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

I think you are trying to make this much harder than it is. I do radar imaging and the process is the same.

We have had undergraduates working with the location algorithms.

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

See above.

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.

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:

Uncle Henry wrote: 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 wrote: .. 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

Here is another interesting document on how GPS works...

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These are my opinions, not necessarily my employer\'s.  I hate spam.

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

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.

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.

Not quite, here's how the aviation system actually works.

A bunch more details at:

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Jim Pennino

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Standard math.

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).