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Are accurate clocks really the limiting factor in cheap Inertial Navigation?
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rs20:
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.
Berni:
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.
tomato:
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.
soldar:

--- Quote from: jc101 on March 25, 2019, 05:29:17 pm ---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.

--- End quote ---


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 gives 106.62965,
This page gives 106.652,
Google Earth says 106.66034.
Maybe the airport is moving around?

This photo'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.
soldar:

--- Quote from: RoGeorge on March 25, 2019, 06:30:13 pm ---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.
--- End quote ---

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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