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Old 07-07-2012, 17:59   #31
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Re: Will this make GPS obsolete?

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Originally Posted by David M View Post
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.
Why not take a picture then count the pixels between the heavenly body and the visible horizon. Knowing the lens focal and the sensor's dia you can tell the angle.

Too simple?

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Old 07-07-2012, 18:13   #32
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Re: Will this make GPS obsolete?

If my mobile reads "no signal" then I think I am offshore.

When it starts showing signal again, I know we are nearly somewhere.

Then who needs a GPS?

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Old 07-07-2012, 18:18   #33
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Re: Will this make GPS obsolete?

When you see birds you know you're close to land.
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Old 07-07-2012, 18:31   #34
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When you see birds you know you're close to land.
When the birds have memorized your credit card number it's time get back to sailing. See works both ways.
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Old 07-07-2012, 18:43   #35
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Re: Will this make GPS obsolete?

I like the idea of a cell phone app that will give you a position by taking a photo of the sky. My phone will already tell me the time, take a picture, measure angles, has a compass and identifies stars. Sounds like most of the tools are already there.
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Old 07-07-2012, 19:01   #36
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Re: Will this make GPS obsolete?

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Why not take a picture then count the pixels between the heavenly body and the visible horizon. Knowing the lens focal and the sensor's dia you can tell the angle.
I helped develop a patent doing something like that but not with stars. You just can't get the resolution and horizon reference well enough to beat a sextant. A sextant optically is so far ahead of a digital camera. Our cameras were top of the line Sony video fixed and wired to GPS corrected to a base station filled in with a ring laser gyro. We could compute positions seen in the cameras from a vehicle moving down the freeway to within 4 inches at 100 yards absolute to the planet. We relied on the GPS and ring laser to compute the baseline then triangulate the position of an object in the distance from multiple images. To do that with star shots would be far more complicated given GPS can do you far better for way cheaper. We knew where we were but wanted to know where what we saw was. The reverse would be a lot more complicated plus you still need a chronometer with some precision.

The concept of something cheaper than GPS for an end user is a joke. The cell phone used to take the picture already has a GPS chip inside it that will do it better. I suppose a panoramic camera could shoot images over time to compute the horizon but the cost of the optics would easily be more than a GPS.

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If my mobile reads "no signal" then I think I am offshore.
Less technology can indicate exactly what you want to know. I love tech stuff but it has to have a reason. We can already build things that have no real purpose.
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Old 07-07-2012, 19:07   #37
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It could have been a CG boat/plane/chopper or repeater station.
Never thought of that! LOL. They just said Coast Guard San Diego. Maybe submarines looking for drug runners...Still it should be he Mexican Navy's job to tell me get off. I'm not operating in US waters. Unless they didn't know...?
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Old 07-07-2012, 19:59   #38
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Re: Will this make GPS obsolete?

The concept is indeed interesting and would be nice if it has more redundancies and could be used in addition with GPS. I agree with Stumble that it is unlikely that the U.S. would turn of GPS however the real problem is that too many use GPS as their primary method of navigation. GPS should confirm what you have plotted on charts using traditional methods.

Situational awareness is essential. Too many check the GPS at most once an hour and if it isn't working they are lost. There are many reasons that may cause GPS to not work including electrical failure, equipment failure, faulty data, etc. Worse, the GPS itself could cause false readings. Recently the British MOD (ministry of Defense) announce that during a recent two week exercise GPS might not work or worse, IT MAY PROVIDE FALSE SIGNALS! Think James Bond in the Tomorrow Never Dies. This isn't just Hollywood though and recently the Iranians may have brought down one of our drones by doing just this. Also, at the University of Texas, a professor and his students found they could take control of drones by modifying GPS. Admittedly this hasn't affected yachtsmen much if at all but it would be nice to have something that provides redundancy.

There is another way to provide redundancy and that is to use what is tried and true; charts and a sextant when taking long cruises. If nothing else, you can use them if the GPS fails and you have situational awareness.
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Old 07-07-2012, 20:53   #39
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Re: Will this make GPS obsolete?

Situational awareness is essential.
+1
I've sailed past many a boat with no one in the cockpit, Everyones below using all of their computers/plotters/GPS all wired to their autopilot. They'd seem surprised that I'd hail them on the VHF to see if everything was alright,
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Old 07-07-2012, 21:04   #40
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Re: Will this make GPS obsolete?

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I'm waiting on the iPhone app that photographs the stars and applies some algorithm to geolocate you
Now that's the ticket!!!
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Old 07-07-2012, 21:11   #41
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Re: Will this make GPS obsolete?

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Situational awareness is essential.
+1
I've sailed past many a boat with no one in the cockpit, Everyones below using all of their computers/plotters/GPS all wired to their autopilot. They'd seem surprised that I'd hail them on the VHF to see if everything was alright,
I flew from purse seiners out of Guam for three years, I approached a RORO in the middle of the Pacific and NO one was in sight. Hovered around the bridge for several minutes and saw not a soul. I am convinced that if you do not have radar and LOOK that you may very well be history... This ship was moving at about 18 knots...
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Old 07-07-2012, 21:18   #42
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Re: Will this make GPS obsolete?

Just out of curiosity, has the civilian side of GPS ever been shut down. Believe I remember it's accuacy being degraded but don't remember anything about GPS going down completely. The degraded signal still gave accuracy to something like 500' just not the ability to put a bomb in some jihadi's turban. For those of us who've cruised with only sextant and a DR plot, 500' CEP fix seems a miracle.
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Old 07-07-2012, 21:31   #43
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Re: Will this make GPS obsolete?

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Just out of curiosity, has the civilian side of GPS ever been shut down. Believe I remember it's accuacy being degraded but don't remember anything about GPS going down completely. The degraded signal still gave accuracy to something like 500' just not the ability to put a bomb in some jihadi's turban. For those of us who've cruised with only sextant and a DR plot, 500' CEP fix seems a miracle.
It will not be shut down completely. Your fix accuracy is correct!
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Old 07-07-2012, 22:52   #44
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Re: Will this make GPS obsolete?

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Originally Posted by roverhi View Post
Just out of curiosity, has the civilian side of GPS ever been shut down. Believe I remember it's accuacy being degraded but don't remember anything about GPS going down completely. The degraded signal still gave accuracy to something like 500' just not the ability to put a bomb in some jihadi's turban. For those of us who've cruised with only sextant and a DR plot, 500' CEP fix seems a miracle.
I think it was Pres. Clinton who decided that selective availbity was a no-no. The military receives a different microwave freq. that seems to be working rather well for them.
The Russians and Chinese and others have their own GPS systems.
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