EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: rs20 on March 25, 2019, 01:33:13 pm
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Hi,
In this article (https://phys.org/news/2019-03-scientists-closer-clock-gps-galileo.html), in which scientists have apparently developed some sort of portable atomic clock, they claim that with this clock, the need for GPS satellites is rendered obsolete:
Dr. Alessia Pasquazi from the EPic Lab in the School of Mathematical and Physical Sciences at the University of Sussex explains the breakthrough: "With a portable atomic clock, an ambulance, for example, will be able to still access their mapping whilst in a tunnel, and a commuter will be able to plan their route whilst on the underground or without mobile phone signal in the countryside. Portable atomic clocks would work on an extremely accurate form of geo-mapping, enabling access to your location and planned route without the need for satellite signal.
Now of course you need more than just the time to figure out one's location; on the surface these claims make no sense. I sent an email to the author for clarification, and got this response:
Long story short, precision clocks are needed for what is called 'inertial navigation', where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
So in short, the claim is that we could have dead reckoning, non-satellite backed INS systems in our cars (maybe even mobile phones), except for one hurdle: modern (quartz?) clocks being too inaccurate. My intuition/understand was the MEMS 6-axis sensors, while amazing feats of engineering, aren't all that accurate and certainly aren't hampered by the inaccuracies presented by a quartz clock.
Is my understanding out of whack? Or are the claims in the link completely unreasonable?
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Even when the time is absolute correct then still the smallest error from the accelerometer will keep multiplying, so I don't see how this is going to work. If you use it in a car and keep correcting based on where the roads are.. .maybe.
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Does not make sense to me too.
Sure time is a factor, but we can already make very precise TCXOs that are easily orders of magnitude more accurate than needed. But accelerometers and gyroscopes are way too noisy and drifty to make this work. Acceleration integrated gives you velocity and velocity integrated gives you position. Any slight offset error in the accelerometer causes the velocity integral to drift away in time, and since this feeds into another integrator it means it will drift faster and faster until it just flies off towards infinity. Its an incredibly unstable system.
We do make use of intertial navigation tho. Intercontinental missiles for one have a dead reckoning system that allow the missile to keep on course even if all outside navigation signals are jammed. But they use very fancy accurate accelerometers and special light interferomentry gyroscopes to get it accurate enough to not drift off in the few minutes it takes the missile to hit the target.
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In every navigation application I have encountered clock errors are several orders of magnitude below the other error sources. By my rough estimate even the incredibly exotic inertial navigation systems used in submarines have at least an order of magnitude between the clocks and other error sources, though I don't really have any definitive information on the components of those systems.
While he didn't admit it to you, the professor may have one real application up his sleeve which he is hiding for proprietary reasons. A really good clock can be used to estimate altitude. Which combined with a known starting position, good geodata and a crude inertial system could give you excellent results. Unclear how much better they would be than a similar system with just the known start, good geodata and a crude inertial system. My GPS units do a pretty good job of estimating position in tunnels based on these types of inference.
But my own prejudice, based on many encounters with research professors, is that they are often incredibly naive outside their specific expertise and that he had never actually dealt with real world errors in navigation systems. My favorite example of this naivety came in a grad class in the early 1980's. The prof was actually a noted expert in his field and as well as I could judge the reputation was well earned. But my respect for his overall knowledge came when he announced in class that there was a new invention out, something called a microprocessor that might someday allow data operations in small fielded units. Many of us in the class were already employed in industry and had fielded such devices years ago. The prof was at least three product cycles behind the curve.
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But accelerometers and gyroscopes are way too noisy and drifty to make this work.
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very fancy accurate accelerometers and special light interferomentry gyroscopes
I'd agree that some other very accurate other stuff is needed as well as the accurate time. Perhaps they haven't figured them out yet so they thought it best not to mention them.
"which range from partnerships with the UK aerospace industry, which could come to fruition within five years,"
Sounds like they're after another 5 years of funding!
"We will be starting work on these projects on 1st December 2014 (i.e. next Monday) and the initial funding is for five years."
https://telescoper.wordpress.com/2014/11/26/quantum-technologies-at-sussex
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Accurate, long term dead reckoning is a staggering technical challenge. Even the most accurate (read: and most expensive) inertial navigation systems have some sort of recalibration technique back to a reliable reference. Spacecraft and military aircraft, for example, have (had) optical systems that reset their INS's based on the positions of reference stars. I'm at least as impressed by the design of those optical miracles as I am by the INS's they are (re)calibrating. If INS's with those kinds of budgets still weren't accurate enough over time to not require external references, I'm confident no MEMS sensor is either. At least today.
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You can't render GPS satellites obsolete until your atomic clock, and all the kit needed to go with it, can match the tiny power consumption of a current GPS receiver. People have come to expect a really high level of portability.
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Tho it does make me wonder how hard is it to make a optical fiber interferometry gyroscope. Perhaps something along the lines of shining the laser head of a CD drive into a coil of fiberoptic cable since CD drive laser assemblies are pretty much cheap tiny interferometers.
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Tho it does make me wonder how hard is it to make a optical fiber interferometry gyroscope. Perhaps something along the lines of shining the laser head of a CD drive into a coil of fiberoptic cable since CD drive laser assemblies are pretty much cheap tiny interferometers.
Most optical gyros don't actually use fibre, because they can achieve greater stability by reflecting light off mirrors. The base plate and mirrors form quite a heavy assembly, to achieve the rigidness needed for accurate navigation.
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Ring gyros are a fun topic. Their challenge is loss of registration due to extremely slow rotation rates... there is always some rate of rotation small enough that the pattern shift is smaller than the resolution of your sensor.
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Most optical gyros don't actually use fibre, because they can achieve greater stability by reflecting light off mirrors. The base plate and mirrors form quite a heavy assembly, to achieve the rigidness needed for accurate navigation.
There are versions that use a single piece of Pyrex, with the mirrors silvered directly onto polished faces in the proper alignment. Solves quite a few challenges with respect to thermal stability, etc.
However, my earlier comments regarding the sensor still apply. That's where the real challenge lies, in having sufficiently high enough sensor resolution to not lose registration due to very low rotation rates.
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Inertial navigation was accurate enough to hit London from the west coast of the Netherlands in WW2.
The amount of drift you can expect of "modern" sensors is related to price you pay for them.
One way you could copensate for drift in road traffic is to map the accumulated data to the road map, ans assume you can only travel over the roads.
If you accumulate enough left and right turns you could even get the location from that even without prior knoledge about the starting position.
No atomic clocks needed.
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There is a reason why part of the checklist in aviation is to verify the position of an aircraft before departure, all gates have their specific Lat Long available as cross check. This is to verify the aircraft INS (Internal Navigation System) which does dead reckoning has a known staring point. It will drift during the flight. The INS is one navigation system, and it combined with radio Nav beacons and GPS.
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Inertial navigation and time consuming journeys don't go together very well. An ICBM can reach its target accurately by inertial navigation. A bomber needs corrections, manually applied, along the way. A cruise missile uses inertial navigation to move between way points, where it uses a ground mapping radar to realign itself against a stored map.
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Ring gyros are a fun topic. Their challenge is loss of registration due to extremely slow rotation rates... there is always some rate of rotation small enough that the pattern shift is smaller than the resolution of your sensor.
That isn't quite the problem. The detectors have plenty of resolution to detect a small fraction of a fringe. The problem is that at DC, the two modes (clockwise and anticlockwise) are close enough in frequency to cause injection locking of the laser from scattered light or other means of crosstalk, This leads to zero signal. The usual (partial) solution is to mechanically dither the gyro. This isn't perfect and also introduces a signal you have to filter out.
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If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location. It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line). Many methods were presented. One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.
Very long but interesting documentary/dramatization:
https://www.youtube.com/watch?v=LHvt48S9l4w (https://www.youtube.com/watch?v=LHvt48S9l4w)
In theory, an extremely precise clock can be used for inertial navigation (without reference stars). In practice, it won't be easy to beat the GPS.
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Clocks were a huge problem a couple of hundred years ago. Not so much today. The magnitude of the time error in celestial observation is roughly the rotation rate of the earth surface in the celestial reference times the time error. More or less 500 meters per second of error. For a garden variety quartz wristwatches that means about 250 meters of position error per day since last setting of the clock. For high precision wristwatches that becomes something more on the order of 500 meters per month. Go to a commercial Rubidium standard and you cut those errors by another couple orders of magnitude.
For an accelerometer to contribute the same 250 meters per day as the garden variety wristwatch it has to have offsets and gain errors on the order of 3E-08 g. Such accelerometers are not garden variety. Similar story for rate sensors.
For those who like laser ring gyros look up Sagnac effect.
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exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
I read it: there might be some super duper technology in the future which certainly wouldn't be possible without our invention and although it may still not happen with our invention if it does happen it will totally be some awesome stuff. And we gotta invent some impressive sounding justification for our research to make beancounters happy.
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Inertial navigation was accurate enough to hit London from the west coast of the Netherlands in WW2.
The amount of drift you can expect of "modern" sensors is related to price you pay for them.
true only if path is near straight line or nice parabolic as errors dont accumulate that much. retry with zig zag motion, the rocket may end up in seabed or top mountain desert, if not on civilians occupied area. as mentioned, even the most expensive spaceship will need correction based on landmark or beacon/gps. if this idea is correct, people should have already proved the concept with special vehicle setup with Cesium clock on board. the portable atomic clock maybe just a dream or another 21st century buzz. but then an "atomic gyroscope" maybe something else.
One way you could copensate for drift in road traffic is to map the accumulated data to the road map, ans assume you can only travel over the roads.
If you accumulate enough left and right turns you could even get the location from that even without prior knoledge about the starting position.
it may work as this is not purely dead reckoning. a simple AI, or path alignment can be embedded as driver can still see the road. pure dead reckoning may end up vehicle turning into grass field, not with a human driver.
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It seems strange that a University of Sussex dept. the Prof. and phys.org don't realize that a lot more than a miniature atomic clock is needed for the none-GPS ambulance or mobile phone navigation, but we all do!
Debunked. :)
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A quick Google search turned up a portable cesium clock introduced by Symmetricon in 2011 that is the size of a matchbox, weights 35 grams and uses 115 mw of power. It's based on work done by NIST.
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That said, one application I can see for cheap/portable atomic clocks is not really dead reckoning, but navigation based on local beacons where a GPS clock isn't available even to the beacons. So for indoor underground positioning you could deploy fixed local beacons and allow mobile receivers to triangulate relative to those beacons. Or you could do the reverse for wireless network monitoring. In a mesh wifi network, each client can be seen by a handful of APs. They could in principle do triangulation to allow you to locate unidentified devices or rogue APs. Like GPS you would still have to periodically update the clocks due to their non-zero drift, but a cesium clock would have less drift than an OCXO.
I am still skeptical. Inexpensive portable rubidium oscillator already exist, and as I recall the stability crossover point between a Rb oscillator and a GPS signal is several hours which is plenty of leeway to keep your mesh network synchronized.
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The only use I can see is to augment GPS signals - if you know the time accurately then you have one less unknown in your solution. Kalman filters and all that stuff. But going from a few ppm time error to 0 isn't going to change much.
When I was working on a system for trucks that used counting hubometers as an absolute distance reference, tire pressure and even tread wear were visible in the data. The firmware had to calibrate the tire size when travelling in a constant direction for a long enough interval and long enough distance, while GPS fix was maintained, and could then use that value when GPS was lost.
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It seems strange that a University of Sussex dept. the Prof. and phys.org don't realize that a lot more than a miniature atomic clock is needed for the none-GPS ambulance or mobile phone navigation, but we all do!
Maybe you and all the others that "know better" should read what the author wrote:
Long story short, precision clocks are needed for what is called 'inertial navigation', where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
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Maybe you and all the others that "know better" should read what the author wrote:
Long story short, precision clocks are needed for what is called 'inertial navigation', where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.
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The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.
I don't follow that logic.
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.
I don't see them trying to take credit for anything other than the advances they've made with small clocks.
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.
The authors aren't trying to convert an existing iPhone to an inertial guidance device. The MEMS sensors aren't the main bottleneck because better technology exists.
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The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.
I don't follow that logic.
So what does the word "first" mean in this context then? She also says "research by our colleagues on quantum gyroscopes should make this thing even better". If the quantum gyroscope makes it even better, then that implies that this innovation is useful on its own. If I really have to spell it out for you:
- "Thing A improves performance by 200%. Thing B makes it even better!" <-- Second sentence makes sense.
- "Thing A isn't immediately applicable or useful on its own. Thing B makes it even better!" <-- Second sentence makes no sense whatsoever.
Ergo, by contradiction, the sentence "Thing B makes it even better!" implies that the thing mentioned before hand is applicable or useful on its own.
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.
I don't see them trying to take credit for anything other than the advances they've made with small clocks.
Dude, they're saying "now ambulances can navigate in tunnels and we don't need satellite signals anymore". If they're not claiming the credit for those improvements, are they just rambling irrelevant BS then?
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.
The authors aren't trying to convert an existing iPhone to an inertial guidance device. The MEMS sensors aren't the main bottleneck because better technology exists.
So go on then, tell me a angular rate sensor that is more accurate than MEMS, and affordable and small enough to fit in a mobile phone? Answering THAT question is the FIRST bottleneck, not clocks.
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So what does the word "first" mean in this context then? She also says "research by our colleagues on quantum gyroscopes should make this thing even better". If the quantum gyroscope makes it even better, then that implies that this innovation is useful on its own. If I really have to spell it out for you:
- "Thing A improves performance by 200%. Thing B makes it even better!" <-- Second sentence makes sense.
- "Thing A isn't immediately applicable or useful on its own. Thing B makes it even better!" <-- Second sentence makes no sense whatsoever.
Ergo, by contradiction, the sentence "Thing B makes it even better!" implies that the thing mentioned before hand is applicable or useful on its own.
When one states Thing A is the first bottleneck, it (generally) means there are several bottlenecks, but Thing A is presently setting the limit for performance.
When the authors state "research by our colleagues on quantum gyroscopes should make this thing even better" it likely means that recent advances in quantum gyroscopes have improved their performance, i.e the limits imposed by the second (or third?) bottleneck has become even less of an issue.
Dude, they're saying "now ambulances can navigate in tunnels and we don't need satellite signals anymore". If they're not claiming the credit for those improvements, are they just rambling irrelevant BS then?
There is nothing in that sentence that indicates the authors are claiming credit for everything. In fact, they have explicitly praised their colleagues for improvements in the quantum gyros.
So go on then, tell me a angular rate sensor that is more accurate than MEMS, and affordable and small enough to fit in a mobile phone? Answering THAT question is the FIRST bottleneck, not clocks.
The whole point of the article is that, with their breakthrough, the clock will no longer be the first bottleneck. Replacing the MEMS may take over the position of first bottleneck.
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OK, but the fact appears to be that even before any of the mentioned advances, quartz crystals are NOT the bottleneck. I repeat, the clock already isn't the first bottleneck. The MEMS sensors have been the bottleneck all along.
So if you get the impression from the article that quartz crystals used to be the bottleneck, but due to their breakthrough, MEMS sensors are the new bottleneck, then you've been duped by the dishonesty of the article. It is this dishonesty, along with the implication in the original article that their advance makes satellite-less INS feasible, that I'm questioning in this thread.
I mean, looking back at the article, I see they're using words like "one step closer" in various places. So maybe my objection wouldn't hold up in a strictly technical court of law. But that doesn't make it any less slimy or clickbaity. Also, "without the need for satellite signal" is a bloody great stretch given that even the best INS's need occasional feedback, which is almost always from GPS satellites or star trackers.
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OK, but the fact appears to be that even before any of the mentioned advances, quartz crystals are NOT the bottleneck. I repeat, the clock already isn't the first bottleneck. The MEMS sensors have been the bottleneck all along.
So if you get the impression from the article that quartz crystals used to be the bottleneck, but due to their breakthrough, MEMS sensors are the new bottleneck, then you've been duped by the dishonesty of the article. It is this dishonesty, along with the implication in the original article that their advance makes satellite-less INS feasible, that I'm questioning in this thread.
I mean, looking back at the article, I see they're using words like "one step closer" in various places. So maybe my objection wouldn't hold up in a strictly technical court of law. But that doesn't make it any less slimy or clickbaity. Also, "without the need for satellite signal" is a bloody great stretch given that even the best INS's need occasional feedback, which is almost always from GPS satellites or star trackers.
This device involves clocks based on optical combs and accelerometers based on atom interferometers. Quartz clocks and MEMS aren't the bottlenecks -- they aren't even in the discussion.
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Quartz clocks and MEMS aren't the bottlenecks of today's mobile phone INS systems. OK then. Lol. I guess any illusion I had that you weren't just a troll has completely evaporated at this point.
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Todays mobile phones can do rough navigation without a GPS signal anyway. They use the precise time of flight measurement to the cell towers to triangulate the rough position and then refine it a bit using wifi access points. Google maintains a map of them by combining the telemetry data from phones and then feeds that map back to the phones in order to use it for triangulation.
This same system is also used to "hot start" the GPS receiver when needed. This rough location is combined with precise time and orbital data from the internet. With all of this the GPS receiver can calculate the distance to each satellite, telling it exactly where to look for a signal correlation and letting it lock on to the signal near instantly. Once it has a lock it can actually measure the distance to satellites and refine the location down to the usual GPS accuracy. This is why GPS in phones still works fine inside a car without even being on the dash or having a nice big GPS antenna that the usual standalone GPS satnavs needed.
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Okay, I'll try again...
The device the authors would like to build requires very high performance components. First, it requires an optical clock. (A Rubidium or Cesium clock or a Hydrogen maser would not be good enough.) Second, it requires a quantum gyroscope / atom interferometer. (A laser gyro would not be good enough.) The performance levels of quartz clocks and MEMS are many orders of magnitude below what is required for the planned device, so they are not part of the discussion. They are not bottlenecks for the simple reason that they can not ever be used in this device. Which one functions as the bottleneck in a present-day mobile phone is irrelevant.
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There is a reason why part of the checklist in aviation is to verify the position of an aircraft before departure, all gates have their specific Lat Long available as cross check. This is to verify the aircraft INS (Internal Navigation System) which does dead reckoning has a known staring point. It will drift during the flight. The INS is one navigation system, and it combined with radio Nav beacons and GPS.
Where was that photo taken? At first sight I guessed somewhere in SE Asia but putting those coordinates (10º 49' 06''N, 105º 54' 43''E) into Google it takes me to a rice field in South Vietnam. I guessed the most probable error was in longitude and found Ho Chi Ming City airport at the same latitude but about 45 NM to the east.
Sign says: 105.911944°,
This page (https://latitude.to/map/vn/vietnam/cities/ho-chi-minh-city) gives 106.62965,
This page (https://www.prokerala.com/travel/airports/viet-nam/tan-son-nhat-international-airport.html) gives 106.652,
Google Earth says 106.66034.
Maybe the airport is moving around?
This photo (https://www.alamy.com/stock-photo-castellon-spain-09th-mar-2016-a-sign-featuring-coordinates-pictures-98780546.html?pv=1&stamp=2&imageid=355A28A8-305D-4CF4-9C96-CCD23AC26F67&p=173981&n=0&orientation=0&pn=1)'s coordinates also do not match. The longitude is off by a certain distance.
Internet sources confirm Google Earth uses WGS84 datum and aviation uses the same datum (as you would expect). I am very curious about this. Maybe some aviator can explain the discrepancy.
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If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location. It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line). Many methods were presented. One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.
This is incorrect and it seems you do not understand how astronavigation works. I am quite knowledgeable about astronav and it is quite too long and complicated to explain how it works in a short post but let us simplify and say the chronometer tells you the time at the prime meridian and the astronomical observations are an indication of the local time and the difference tells you you geographical longitude. Again, that is a huge distortion/simplification but the observations were not used to reset or calibrate the chronometer at all. That is not how it works. If the astronomical observation was used to set or correct the chronometer then ... you wouldn't need the chronometer at all. The astronomical observation tells you local time and the chronometer tells you Greenwich time.
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If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location. It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line). Many methods were presented. One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.
This is incorrect and it seems you do not understand how astronavigation works. I am quite knowledgeable about astronav and it is quite too long and complicated to explain how it works in a short post but let us simplify and say the chronometer tells you the time at the prime meridian and the astronomical observations are an indication of the local time and the difference tells you you geographical longitude. Again, that is a huge distortion/simplification but the observations were not used to reset or calibrate the chronometer at all. That is not how it works. If the astronomical observation was used to set or correct the chronometer then ... you wouldn't need the chronometer at all. The astronomical observation tells you local time and the chronometer tells you Greenwich time.
I never said how astronavigation works, but I admit it's all my fault for not phrasing properly what I was thinking at at that moment. I was trying to imagine an inertial navigation where the accumulated errors are reset from time to time using astronavigation.
Please let me try again the phrase you quoted:
If you have a precise clock and are allowed to look at the stars [thus calculating the position using astronavigation instead of inertial navigation in order] to recalibrate [the position and reset the errors accumulated by the inertial navigation system], than then it's possible to find out the precise location [using mostly inertial navigation, and only rarely recalibrate the position using astronavigation, assuming most of the errors will be caused by the inertial system, and not the timekeeping system].
[New paragraph, and then the link to a documentary about how precise timekeeping enabled the possibility of astronavigation at open sea].
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Astronav does not have the precision to correct other more advanced technologies. A good navigator, with a good sextant, on a good day, on a very stable platform (not on a rolling ship), might get a fix with an error of 200 - 500 m. Figure in bad conditions and cloudy days and it is a non-starter.
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A quick Google search turned up a portable cesium clock introduced by Symmetricon in 2011 that is the size of a matchbox, weights 35 grams and uses 115 mw of power. It's based on work done by NIST.
And is not as good as a decent OCXO... lower power, maybe smaller, but not as stable. And it is not a cesium primary reference... it is like a rubidium oscillator that uses cesium... and costs a butt load 'o bucks.
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I use the noise from the low order bits from a MEMS INS board accelerometer, gyro, and compass data in my true random number generator. The output from that TRNG passes every statistical randomness test. MEMS chips are useless for anything but low precision applications.
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Call me cynical, but...
Stated problem this solves: We need a technology breakthrough to know where ambulances are in tunnels!
Proposed solution #1: We need new tech for an ultra-precise time reference to enable an ultra-precise Inertial Navigation System
Proposed solution #2: We could add a CANBUS interface to the navigation system so it can read the odometer and to deduce location when GPS signal is not present
Maybe the unstated real problem: We need equivalent GPS navigation functionality for times when the GPS system is either down, cannot be trusted, or is being denied through jamming or other Electronic Counter Measures. However we also need to attract funding.
I'm slightly surprised that they haven't also mentioned it would be useful for cave and/or mine rescues...
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Call me cynical, but...
Stated problem this solves: We need a technology breakthrough to know where ambulances are in tunnels!
Proposed solution #1: We need new tech for an ultra-precise time reference to enable an ultra-precise Inertial Navigation System
Proposed solution #2: We could add a CANBUS interface to the navigation system so it can read the odometer and to deduce location when GPS signal is not present
Maybe the unstated real problem: We need equivalent GPS navigation functionality for times when the GPS system is either down, cannot be trusted, or is being denied through jamming or other Electronic Counter Measures. However we also need to attract funding.
I'm slightly surprised that they haven't also mentioned it would be useful for cave and/or mine rescues...
I just think you aren't cynical enough. It is a three step process.
1. I want to play in this sandbox.
2. I am not creative enough to come up with real applications for my pet rock.
3. Funding requires some applications, so just throw whatever I read in popular magazines and trade journals at the problem.
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I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.
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I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.
any person who designed navigation related system know they want to use any possible technological advancement. the classical method is three, dead reckoning algorithm, landmark and beacon. i'm not an expert in GPS but the way i see it, it can be classified as beacon, beacon usually man made for this specific purpose. landmark as mentioned natural star formation, land features (mountains, trees, holes, building, signage etc). triangulation is beacon from comm towers, including your LORAN. dead reckon incl MEMs/INSs sensors, math, cpu and the discussed clocking system. so, nobody ridicule anything if it can help navigation, this is human's life related. except the article in OP and author writing you've highlighted with their "atomic clock buzz no GPS needed" campaign.
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I was skeptical of GPS when I first heard of it. Not because LORAN was already here. LORAN has obvious limits, starting with coverage. What I questioned was whether anyone less well funded than the military could deal with all those receivers and the computation in a portable package. Fortunately I underestimated the impact of Moore's law.
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The best mechanical gyroscopes (ie Sperry) did <1degree error in 1 hour, afaik. The mechanical gyroscopes provide the "attitude" to a ref frame, while the MEMS gyroscope outputs the "angular velocity". I would rather not dead recon with a MEMS based system even having atomic clock on the chip :)
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((( quietly hoping somebody else posts a link to today's XKCD, that I just read and LOL to )))
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I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.
I am not sure if you are serious or what point you might be trying to make but
(1) the capabilities of satelite navigation compared to LORAN are immensely greater. Satnav systems were first developed for missiles, submarines and surface naval ships in circumstances where LORAN could not be used.
(2) GPS did not replace LORAN but earlier satnav Transit (https://en.wikipedia.org/wiki/Transit_(satellite)) and
(3) satnav has proven useful enough that Russia (https://en.wikipedia.org/wiki/GLONASS), China (https://en.wikipedia.org/wiki/BeiDou_Navigation_Satellite_System) and the EU (https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)) have all developed their own satnav systems.
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Indeed, the GPS system is very important because it answers the first 2 most important human questions:
1. Where am I?
2. What time is it?
Ufortunatly, it doesn't answer the 3'rd one:
3. WTF, am I doing here?
:-DD
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I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.
I am not sure if you are serious or what point you might be trying to make but
(1) the capabilities of satelite navigation compared to LORAN are immensely greater. Satnav systems were first developed for missiles, submarines and surface naval ships in circumstances where LORAN could not be used.
(2) GPS did not replace LORAN but earlier satnav Transit (https://en.wikipedia.org/wiki/Transit_(satellite)) and
(3) satnav has proven useful enough that Russia (https://en.wikipedia.org/wiki/GLONASS), China (https://en.wikipedia.org/wiki/BeiDou_Navigation_Satellite_System) and the EU (https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)) have all developed their own satnav systems.
This is post hoc reasoning. When GPS was being developed the receivers looked so large, heavy, complex and expensive it was far from obvious that it would ever be really compact and cheap. Most people assumed Loran, Decca and other existing systems would have a long life serving people who couldn't live with the drawbacks of GPS. However, just as GSM was developed to be a car telephone system until around 2000, yet resulted in light handhelds in the early 1990s, GPS moved far quicker than most people expected.
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1921 FACT CHECKER
(https://imgs.xkcd.com/comics/1921_fact_checker.png)
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This is post hoc reasoning. When GPS was being developed the receivers looked so large, heavy, complex and expensive it was far from obvious that it would ever be really compact and cheap. Most people assumed Loran, Decca and other existing systems would have a long life serving people who couldn't live with the drawbacks of GPS. However, just as GSM was developed to be a car telephone system until around 2000, yet resulted in light handhelds in the early 1990s, GPS moved far quicker than most people expected.
I do not see in my post any reasoning at all, mush less "post hoc" , "et cetera" or "inter alia". I do not see how you post is in disagreement with anything I said in mine and I wonder if you are assuming inferences which are not intended, suggested or even condoned by me.
I used Loran-C for many years, even after GPS was available. When they gave notice that Loran-C would be discontinued I was against it being discontinued. At about that time a bolt of lightning hit my boat destroying all electronics and I took it as a sign from above that the life of Loran really was coming to an end. Obviously I replaced it with a GPS receiver.
In any case the answer to the question "Are accurate clocks really the limiting factor in cheap Inertial Navigation?" the answer is "no".
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Ufortunatly, it doesn't answer the 3'rd one:
3. WTF, am I doing here?
:-DD
apart from the exhaustive neverending quest for that by top notch human being, there is a simple book fully describing that. anyone understanding and applying whats in the book will be fully navigated ;) nevermind the other books, they are hoax.
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Mechatrommer scribbled....
I quote:
"
apart from the exhaustive neverending quest for that by top notch human being, there is a simple book fully describing that. anyone understanding and applying whats in the book will be fully navigated ;) nevermind the other books, they are hoax."
And your referring to The Art of Electronics 2nd Edition ? Used to be marketed as #1 selling book to EEs, with a certain religious text coming in second.... :-*
Having really precise time lets you do very good Dead Reckoning / Inertial. What is more important in the future, is it lets you do it in synchronism with other vehicles/infantry/drones. The US Secretary of Defense said a while back that he is/was working really hard to see that GPS becomes a mere backup, and in fact of such lower importance that it could be handed over to the Department of Transportation for management and funding. That is where the drive for such tiny, precise, clocks come from.. How the rest of that system will work has not been fully discussed, but I can see lots of opportunities for co-operative pseudo-ranging methods using line of site radio ranging.
Steve
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... posts current XKCD "1921 Fact checker", and everybod looks confused....
Darn, it rolled over quicker than I expected. When I looked it was "New Robot":
(https://imgs.xkcd.com/comics/new_robot.png)
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There's almost no comments anywhere on the original article, but here's a couple.
"Can someone explain why a portable atomic clock “allow(s) them to navigate where there is no satellite signal”? Are they going to use a sextant?"
"The abstract says nothing about geolocation, and measuring time with exquisite detail gives you absolutely NO CLUE on where you are, so dear author: could you please explain how it works and/or quote the original authors?"
https://www.theengineer.co.uk/portable-atomic-clocks-navigation/ (https://www.theengineer.co.uk/portable-atomic-clocks-navigation/)