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Old 01-07-2012, 18:44   #16
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Re: Will this make GPS obsolete?

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Originally Posted by capngeo View Post
I'm waiting on the iPhone app that photographs the stars and applies some algorithm to geolocate you
Don, I have seen an app for the iphone, you point the phone in any direction and it gives you the stars. really neat app
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Old 01-07-2012, 19:51   #17
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Re: Will this make GPS obsolete?

The app would need to be able to measure the altitude of the star above the horizon. I don't see how it would be able to do that. It's hard enough to get within a mile with a sextant.

I agree that Star Walk for the iPad is an excellent app.
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Old 01-07-2012, 20:05   #18
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Re: Will this make GPS obsolete?

it does not measure it just shows you the stars and stuff, with names
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Old 01-07-2012, 21:22   #19
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There is an Iphone app which uses the phone's accelerometers to calculate an angle above horizon. You can take sun, moon, and star sights with it by sighting along the phone's edge. Obviously accuracy and precision are poor. I can consistently get a fix within about 30 miles at best on land. Not a lot of help to the navigator!

I wonder how much it would improve with a good sighting path like a sextant provides?
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Old 01-07-2012, 21:54   #20
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Re: Will this make GPS obsolete?

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SOME radio waves are line of site (i.e. VHF).
I keep hearing boating emergencies broadcasted by the USCG while communicating with distressed boaters, but I never receive broadcasts by those boaters in distress even though my antenna is about 30 feet above waterline.

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Old 02-07-2012, 05:35   #21
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Re: Will this make GPS obsolete?

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Does no one else wonder just how this "new technology" works? The article glibly says that it exists, but gives not even a hint of how it uses all these unidentified signals to work out a position.
Most state of he art products combine a number of different technologies (on top of traditional GPS) to achieve max precision indoors and outdoors:

- Use Wifi routers. Requires someone to have mapped the location previously, and recorded how the signal strengths of different hotspots varies with location. Used by Google to position mobile devices that do not have a GPS enabled, for example.

- Use Mobile Cell calls. This starts with a database of known towers and their excat location, and then incorporates calculations of the difference in the power of signal arriving at the mobile from different cell sites. These signal strength measurement are made by the mobile for the purposes of handover management and are reported to the Network in existing Network Measurement Reports (NMR). NMR's are sent about every half second during a call.

- Another technique is Triangulation using Timed signal arrival, which measures the time difference between signals arriving to/from different mobile towers with known locations. Can also be used with TV/Radio tower signals. Or satellites (but then we call it GPS, usually :-) ). Of course LEO satellites could be used too but precision would suffer compared to the GPS satellites which are designd to provide maximum possible precision.
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Old 02-07-2012, 09:52   #22
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Re: Will this make GPS obsolete?

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The short answer is no, it's not going to work very well mid Atlantic. Only medium wavelength signals from shore transmitters are going to be useful, and longer wavelength means less precision in any calculations on position.
True, but when you're in the middle of the ocean knowing your position to the nearest yard isn't all that useful. Until you get into line-of-sight range of land (50 or so miles) you usually don't need a lot of precision.

I remain a bit skeptical, though, as to how this works. How can they calculate a position from a bunch of random radio signals unless they know precisely where all of those signals originated?

In any case, if it actually does work then, yeah, it might replace GPS someday. Or at least serve as a very useful, complementary technology.
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Old 03-07-2012, 01:43   #23
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Re: Will this make GPS obsolete?

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Originally Posted by JesperWe View Post
Most state of he art products combine a number of different technologies (on top of traditional GPS) to achieve max precision indoors and outdoors:

- Use Wifi routers. Requires someone to have mapped the location previously, and recorded how the signal strengths of different hotspots varies with location. Used by Google to position mobile devices that do not have a GPS enabled, for example.

- Use Mobile Cell calls. This starts with a database of known towers and their excat location, and then incorporates calculations of the difference in the power of signal arriving at the mobile from different cell sites. These signal strength measurement are made by the mobile for the purposes of handover management and are reported to the Network in existing Network Measurement Reports (NMR). NMR's are sent about every half second during a call.

- Another technique is Triangulation using Timed signal arrival, which measures the time difference between signals arriving to/from different mobile towers with known locations. Can also be used with TV/Radio tower signals. Or satellites (but then we call it GPS, usually :-) ). Of course LEO satellites could be used too but precision would suffer compared to the GPS satellites which are designd to provide maximum possible precision.
G'Day JW,

That's all very interesting, but does not address the issue of how they arrive at accurate positions at sea, up in the air (drone aircraft) or in buildings which are shielded from RF signals. I think the above situations obviate the usage of cellphone towers or wifi signals. Further, none of the systems that you mention could achieve GPS style accuracy.

I'm still skeptical!

Cheers,

Jim
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Old 05-07-2012, 22:48   #24
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Re: Will this make GPS obsolete?

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I keep hearing boating emergencies broadcasted by the USCG while communicating with distressed boaters, but I never receive broadcasts by those boaters in distress even though my antenna is about 30 feet above waterline.
That's maybe because they communicate on a duplex ship to coast channel?
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Old 05-07-2012, 22:52   #25
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Re: Will this make GPS obsolete?

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G'Day JW,

That's all very interesting, but does not address the issue of how they arrive at accurate positions at sea, up in the air (drone aircraft) or in buildings which are shielded from RF signals. I think the above situations obviate the usage of cellphone towers or wifi signals. Further, none of the systems that you mention could achieve GPS style accuracy.
What I think the system does is use the existing radio signal environment to do a sort of dead reckoning. Ie, as a vehicle moves, the signals it receives from various sources will change in a way that allows you to find out how much and in what direction you moved. The same way you judge your own movement by looking at your surroundings.

To get an accurate fix in the middle of nowhere however you need to know where the transmitters are, and exactly where you are in relation to the transmitters. And that is quite a challenge. To be able to accurately measure the distance between you and ad transmitter you need to use high frequencies, and those are line of sight...
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Old 05-07-2012, 22:58   #26
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Re: Will this make GPS obsolete?

That's my experience. Narely hear the other party. The USCG has signal repeaters as well as more powerful signals.
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Old 06-07-2012, 15:38   #27
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Re: Will this make GPS obsolete?

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I keep hearing boating emergencies broadcasted by the USCG while communicating with distressed boaters, but I never receive broadcasts by those boaters in distress even though my antenna is about 30 feet above waterline.
Mast envy! The USCG has a much bigger stick than you do.

They can hear farther and shoot straighter than you can. Mine is 52 ft and they still can out distance me. VHF is only line of sight EXCEPT when it bounces off thunder storms. I'm down in Yorktown, VA and I get a few calls from Baltimore, MD once in a great while but as you say I never hear the other end. It's not line HAM bands that can bounce off the ionosphere. More power really is not an issue as they just hit dirt or water after so far. It's the stick in the air that matters. The USCG does not violate FCC rules mostly because it wouldn't help.
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Old 07-07-2012, 09:15   #28
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The CG has really good ears! We were in Bahia San Quintin helping to bring a friend in to the anchorage (& avoid the breaking surf spots) and got chastised by the CG that Ch. 16 is only emergency traffic. Responded to them-said sorry. Maybe they knew where we were & wanted to rattle our cage. San Quntin is 60 miles south of Ensenada which is about 70 miles south of San Diego. We have a good radio & antennae is 65 ft up but that was a bit shocking. We had rain the next evening when we hit Ensenada so not sure about the bouncing off clouds but that's the farthest for us!
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Old 07-07-2012, 09:23   #29
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Re: Will this make GPS obsolete?

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The CG has really good ears! We were in Bahia San Quintin helping to bring a friend in to the anchorage (& avoid the breaking surf spots) and got chastised by the CG that Ch. 16 is only emergency traffic. Responded to them-said sorry. Maybe they knew where we were & wanted to rattle our cage. San Quntin is 60 miles south of Ensenada which is about 70 miles south of San Diego. We have a good radio & antennae is 65 ft up but that was a bit shocking. We had rain the next evening when we hit Ensenada so not sure about the bouncing off clouds but that's the farthest for us!
It could have been a CG boat/plane/chopper or repeater station.
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Old 07-07-2012, 09:24   #30
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Re: Will this make GPS obsolete?

considering the age of the article --last year--and the subsequent veto and nix from gummingkt on this topic, i believe e have not too many worries about the accuracy of our gps units due to these radio waves interfering with gummingkt and private gps data --- keep yer bloomers on, guys..is old news.....
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