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Originally Posted by Maninthebar
(Post 10490533)
That source of all error, Wikipedia, says "The term "dead reckoning" was not originally used to abbreviate "deduced reckoning," nor is it a misspelling of the term "ded reckoning." The use of "ded" or "deduced reckoning" appeared much later in history, no earlier than 1931; in contrast to "dead reckoning" appearing as early as 1613 in the Oxford English Dictionary. The original intention of "dead" in the term is not clear however. Whether it is used to convey "absolute" as in "dead ahead," reckoning using other objects that are "dead in the water," or using reckoning properly "you’re dead if you don’t reckon right," is not known"
One might also instantiate "dead on", "dead heat", "dead drunk" in each of which the term 'dead' qualifies as 'absolutely' |
Originally Posted by Euclideanplane
(Post 10490526)
Indeed. I may have misread Vilters, who didn't actually say "only a compass". For dead reckoning you compute the wind triangle using a compass, additionally you need information about wind speed and true airspeed. Which the compass obviously does not provide.
Anyway, GPS provides heading information anyway, in addition to whatever else information you need, so I am not sure I see the point. You use whatever instruments available to tell you where your are and where you are headed. |
Originally Posted by GordonR_Cape
(Post 10490565)
Pedantic mode: Pure GPS does not provide direction, only position. However if you move in a randomly oriented straight line, GPS will tell you which direction you have moved in, and then you can then re-orient yourself to go in the direction you really wanted. Of course most devices (such as modern phones) have a compass and accelerometer.
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Spoke to Collins
They say they still don't know the root cause and have no projected fix time/date.
Originally Posted by swh
(Post 10489821)
Anyone know of a work around for the issues Rockwell Collins 737/757 transponders and GPS have started to exhibit today ? What is the root cause ? |
Originally Posted by lenrand
(Post 10490698)
They say they still don't know the root cause and have no projected fix time/date.
https://www.ainonline.com/aviation-n...ception-outage |
Originally Posted by Maninthebar
(Post 10490568)
Could you derive track from heading, speed and acceleration? I think not. Well I couldn't
GPS gives you a series of positions. Which means, as theory pedants like me will point out, GPS cannot tell you what your airplane (or ship, or cell phone) is doing in terms of course or velocity right now, all it can tell you is what your course and velocity were a little while ago. But now factor in physics. If your course and velocity were to be a whole lot different than what they were one second ago, your neck would have snapped from the acceleration. Since your head didn't snap off your shoulders, we can safely infer that your instantaneous velocity vector right now is not a whole lot different from what it was a little while ago. Factor in reasonable values for a little while and a whole lot and you get pretty tight bounds around what your instantaneous course and velocity are..... |
GPS gives you a series of positions. Which means, as theory pedants like me will point out, GPS cannot tell you what your airplane (or ship, or cell phone) is doing in terms of course or velocity right now, all it can tell you is what your course and velocity were a little while ago. The kalman filter and associated algorithms predict where you are. |
If you are everywhere, there is no need to go anywhere.:p |
Originally Posted by Gauges and Dials
(Post 10490819)
...Which means, as theory pedants like me will point out, GPS cannot tell you what your airplane (or ship, or cell phone) is doing in terms of course or velocity right now, all it can tell you is what your course and velocity were a little while ago.
But now factor in physics. If your course and velocity were to be a whole lot different than what they were one second ago, your neck would have snapped from the acceleration. Since your head didn't snap off your shoulders, we can safely infer that your instantaneous velocity vector right now is not a whole lot different from what it was a little while ago...... |
Originally Posted by Gauges and Dials
(Post 10490819)
GPS gives you a series of positions. Which means, as theory pedants like me will point out, GPS cannot tell you what your airplane (or ship, or cell phone) is doing in terms of course or velocity right now, all it can tell you is what your course and velocity were a little while ago.
GPS does calculate instantaneous velocity -- the velocity right now -- not from a series of positions but by using the doppler shift from each satellite. In fact with just a single reading (from at least four satellites) a GPS receiver can calculate instantaneous position, velocity and time (PVT). With multiple readings, very precise velocity estimates can be obtained by noting how the carrier phase changes between each reading. This is known as Time-Differenced Carrier Phase (TDCP). All subject to the usual GPS errors (hence Kalman filters). |
other oddities
After reading the GPS issue, was interested in what was to be seen on flights takin on the 9th. Nothing of interest appeared to occur which was nice. However, having completed a flight on the 9th, on departure the next day, the radars would not come up. The flight was completed to reposition taking some care to avoid the lumpy bits. Initial checking indicated that the radars were dead (or DED, as applicable). Questioning that, we played with the radar for a while, and found that if we sequenced the systems power up of the radar and GPS, radar worked fine. As the solid state radars are not known for regenerating the magic smoke after auto release, a discussion with the system manufacturer ensued. The OEM was surprised by the behaviour, agreed that solid state units don't exhibit Schrodinger's cat's behaviour. On review, the OEM had a prior history of some 10 failures of this type in 2015 when the system was relatively new, and had introduced a software update to fix the problem. 4 years later, after an overnight, the problem is manifested again. What happened on the 9th?
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Originally Posted by Vilters
(Post 10490495)
Perhaps, I am old school, perhaps my airplane is old school, but in my younger years we had something called a compass.
And you know what? There even was a guy that crossed the ocean with a "compass". => Lindberg in a canvas airframe without heater or aircon and I don't think he had a stewardess to keep him company either. See where technology has brought us? To fly? You need a pilot and an airplane. Every line of software is a line too many. You'll note that Lindberg (and Alcock and Brown) quite literally had the sky to themselves. So technology has brought us the ability to to launch a couple thousand NAT crossings a day. |
Originally Posted by fdr
(Post 10491360)
After reading the GPS issue, was interested in what was to be seen on flights takin on the 9th. Nothing of interest appeared to occur which was nice. However, having completed a flight on the 9th, on departure the next day, the radars would not come up. The flight was completed to reposition taking some care to avoid the lumpy bits. Initial checking indicated that the radars were dead (or DED, as applicable). Questioning that, we played with the radar for a while, and found that if we sequenced the systems power up of the radar and GPS, radar worked fine. As the solid state radars are not known for regenerating the magic smoke after auto release, a discussion with the system manufacturer ensued. The OEM was surprised by the behaviour, agreed that solid state units don't exhibit Schrodinger's cat's behaviour. On review, the OEM had a prior history of some 10 failures of this type in 2015 when the system was relatively new, and had introduced a software update to fix the problem. 4 years later, after an overnight, the problem is manifested again. What happened on the 9th?
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Originally Posted by futurama
(Post 10491198)
GPS does calculate instantaneous velocity -- the velocity right now -- not from a series of positions but by using the doppler shift from each satellite.
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The airline I work for is having this issue. The story we’re getting is that at approximately 3:00z on 6/9/19, the WAAS system on all of the GPS satellites received a software upgrade and that the software upload was somehow corrupted. A plausible explanation from recent Hackaday comments (leap seconds often cause "fun"): Josh says:June 11, 2019 at 7:13 am This particular issue is directly related to certain GPS units from Collins Aerospace (formerly Rockwell Collins). A software design error resulted in the system misinterpreting GPS updates due to a “leap second” event. Collins has advised its customers to not power on the units until June 16, the next scheduled update by the US government to the GPS constellation.
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Originally Posted by FairWeatherFlyer
(Post 10491576)
Are you saying that GPS can accurately calculate GS/VS/direction purely by observing the received, doppler-shifed-due-to-GPS-receiver-movement carrier frequencies from satellites? It would be interesting to read more about this if you have some reference material?
"GPS and other global navigation satellite systems use the Doppler shift of the received carrier frequencies to determine the velocity of a moving receiver. Doppler-derived velocity is far more accurate than that obtained by simply differencing two position estimates." -- GPS World "With respect to the receiver, of course, the satellite is always in motion, but the receiver may be in motion in another sense, in kinematic GPS. It may be on a moving platform, like a vehicle. The ability to determine instantaneous velocity of a moving vehicle has always been one of the primary applications of GPS and it is aided by the Doppler shifted frequency of a satellite signal.In other words, if the platform is moving, there is a relationship between the Doppler shift nominally from the satellite and the change based upon the movement of the vehicle on which the receiver finds itself." -- GPS and GNSS for Geospatial Professionals |
Originally Posted by futurama
(Post 10491604)
"Stand-alone single-frequency GNSS receivers ... estimate velocity either by differencing two consecutive positions ... or by using Doppler measurements related to user-satellite motion. The former approach is the most simple to implement, but it has a meter per second-level of accuracy due to the dependence on pseudorange-based position accuracy. In contrast, Doppler frequency shifts of the received signal produced by user-satellite relative motion enables velocity accuracy of a few centimeters per second." -- GNSS Solutions
"GPS and other global navigation satellite systems use the Doppler shift of the received carrier frequencies to determine the velocity of a moving receiver. Doppler-derived velocity is far more accurate than that obtained by simply differencing two position estimates." -- GPS World "With respect to the receiver, of course, the satellite is always in motion, but the receiver may be in motion in another sense, in kinematic GPS. It may be on a moving platform, like a vehicle. The ability to determine instantaneous velocity of a moving vehicle has always been one of the primary applications of GPS and it is aided by the Doppler shifted frequency of a satellite signal.In other words, if the platform is moving, there is a relationship between the Doppler shift nominally from the satellite and the change based upon the movement of the vehicle on which the receiver finds itself." -- GPS and GNSS for Geospatial Professionals |
Originally Posted by FairWeatherFlyer
(Post 10491576)
Are you saying that GPS can accurately calculate GS/VS/direction purely by observing the received, doppler-shifed-due-to-GPS-receiver-movement carrier frequencies from satellites? It would be interesting to read more about this if you have some reference material?
https://www.researchgate.net/profile...4c78000000.pdf http://researchbank.rmit.edu.au/eser...9492/Zhang.pdf To date, with SA switched off and with the improvement of receiver technologies, velocities of a GPS user can be determined at an accuracy level of centimetres per second, which are several orders of magnitude higher than that of the positions. Moreover, the velocities can be measured at a relative high sampling rate, say from 10Hz to 100Hz P.S. Thanks to @futurama for pointing this out earlier in the thread. |
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