GHA
Well-known member
.. the technology might be of interest to a small handful of people on here. 
1cm GPS accuracy? Not really on a boat but...
- Thread starter GHA
- Start date
wonkywinch
Well-known member
It's already in use in aviation to permit approaches to conventional instrument landing system minima using aircraft GPS, it's called GBAS Landing System (or GLS).
What's the deal with GLS approaches?
What's the deal with GLS approaches?
GHA
Well-known member
After some googling.. the RTK ground based augmentation providing phase information which is used in gbas has been around for quite a while (1993) , discussed in the video, 10:00.
westernman
Well-known member
Maybe if these guys had put the boat on auto-pilot and had a GPS accurate to 1cm they would not have scraped the bridge:-
wonkywinch
Well-known member
It has been around for some time as there was always a determination to filter out the "wobble" the US military used to have on the signal for civilian users. You can still see the effect of that in car sat navs when you leave the planned route, eg a motorway exit. The car sat navs are programmed to assume you are on the road plus or minus a much larger margin which allowed for the wobble without appearing to affect the sat nav's "accuracy". The sat nav will hang onto the road even though you left it before it jumps and recalculates the route.
The US gov (Clinton) then switched off the wobble (called selective availability) in May 2000 and the world went mad for GPS.
GPS.gov: Selective Availability
Stemar
Well-known member
That, of course, would rely on the charts being accurate to 1cm as well - but you've still got a potential error of 2cm.
GHA
Well-known member
Apparently not, it was developed for.. -> "It was at that time, in the early 1990s, when private industry began building on a foundation of RTK development breakthroughs to make hardware and software improvements enabling widespread commercial uses in marine, surveying, mining and construction."
History of RTK—Part 4: Birth of a Utility - The American Surveyor
US5442363A - Kinematic global positioning system of an on-the-fly apparatus for centimeter-level positioning for static or moving applications - Google Patents
The U.S. Army Corps of Engineers working on didn't really need to get round selective availability.
You should ask an AI
wonkywinch
Well-known member
I'm puzzled, you (or rather your AI friend) is agreeing with me surely? I stated there was a determination (by private industry) to filter out the wobble, your link agrees - It was at that time, in the early 1990s, when private industry began building on a foundation of RTK development breakthroughs to make hardware and software improvements enabling widespread commercial uses in marine, surveying, mining and construction.Apparently not, it was developed for.. -> "It was at that time, in the early 1990s, when private industry began building on a foundation of RTK development breakthroughs to make hardware and software improvements enabling widespread commercial uses in marine, surveying, mining and construction."
History of RTK—Part 4: Birth of a Utility - The American Surveyor
US5442363A - Kinematic global positioning system of an on-the-fly apparatus for centimeter-level positioning for static or moving applications - Google Patents
The U.S. Army Corps of Engineers working on didn't really need to get round selective availability.
You should ask an AI
capnsensible
Well-known member
Always felt like it was a small gap going through there on our 33ft yacht!
The Simpsons Bay Yacht Club is a fab place for watching the marine traffic when the bridge opens...
GHA
Well-known member
It doesn't agree with you, RTK was developed to get much greater accuracy needed for the applications mentioned. This accuracy is not available just from a GPS receiver alone then or now, nothing to do with SA. The information of the phase angle received by the ground stations then transmitted to the receiver is discussed on the ytube.
Ask an AI
RobbieW
Well-known member
For the fliers among us, my interest in computing stems from working on BA's Trident fleet in the 70s. They had CatIIIC autoland, takes the aircraft to the gate, and predates GPS by a couple of decades.
A lesson being that little is new, more enhancements to existing technology.
A lesson being that little is new, more enhancements to existing technology.
LittleSister
Well-known member
I remember us being utterly amazed when a friend got an early boat GPS (and that was with selective availability, or whatever). We'd been used to having only an approximate idea of where we were once we were out of sight of land. Now this thing claimed to tell us where we were within something like 20m(?)! We'd previously approached a coast cautiously, peering anxiously ahead looking for lighthouses, prominent buildings and cliffs etc. so that we could be sure we were approaching the correct town. Now this thing could not only tell us which town we were approaching in, but once we'd tied up which part of the harbour and which pontoon we were on. Wizardry!
(Prior to the GPS, he'd had an early marine 'Satellite Navigator', bought off a friend who'd had it for an ocean crossing. When we were in doubt about our position we would watch it anxiously to see whether and when it could find enough satellites for a fix, which was not at all often. Once it indicated it had, it would then take 25 minutes (!) to calculate where it had been at that critical moment, but most often would at long last decide it hadn't enough information after all. I'd swear it made, e.g. crossing the Thames Estuary and its (then seeming) maze of scary sandbanks, shipping channels, swatchways and weird structures more stressful than when we'd previously done it by eye and dead reckoning!)
GPS is already too accurate for my purposes. My venerable Standard Horizon CP180i has been a brilliant bit of kit, but one of its three shortcomings is that the refresh rate is far too fast, so it recalculates a position something like every two or three seconds (and that's in the 'slow' mode), during which the boat will have rolled in one direction or another, and slowed or sped up slightly as it climbs or descends waves/swells, so it's idea of the heading and speed (and hence time to go) since the last 'position' constantly changes wildly, and you have watch the numbers for a while and mentally calculate an average.
I guess a position to 1cm will be handy when one has a robot to scrub one's decks!
(Prior to the GPS, he'd had an early marine 'Satellite Navigator', bought off a friend who'd had it for an ocean crossing. When we were in doubt about our position we would watch it anxiously to see whether and when it could find enough satellites for a fix, which was not at all often. Once it indicated it had, it would then take 25 minutes (!) to calculate where it had been at that critical moment, but most often would at long last decide it hadn't enough information after all. I'd swear it made, e.g. crossing the Thames Estuary and its (then seeming) maze of scary sandbanks, shipping channels, swatchways and weird structures more stressful than when we'd previously done it by eye and dead reckoning!)
GPS is already too accurate for my purposes. My venerable Standard Horizon CP180i has been a brilliant bit of kit, but one of its three shortcomings is that the refresh rate is far too fast, so it recalculates a position something like every two or three seconds (and that's in the 'slow' mode), during which the boat will have rolled in one direction or another, and slowed or sped up slightly as it climbs or descends waves/swells, so it's idea of the heading and speed (and hence time to go) since the last 'position' constantly changes wildly, and you have watch the numbers for a while and mentally calculate an average.
I guess a position to 1cm will be handy when one has a robot to scrub one's decks!
GHA
Well-known member
Same here as described in the ytube, the physics is the same but yet another example of the decentralising of data. Instead of spending many thousands on a base station, build your own for a few hundred & get paid for uploading the data to the web where others can pay to use it.
Boathook
Well-known member
Can't you go into the display settings and dampened down the refresh rate to 15 seconds or such. I did that that with my elderly furuno 31 as otherwise it was a waste of time.
jlavery
Well-known member
And then there was the INS (Inertial Navigation System), which I remember my dad being impressed with as a British Airways Tristar captain. Having to program in the specific departure gate before push-back so that it had the correct starting point...
He started on Constellations with BOAC, as navigator (they had to do a year as navigator, despite being qualified to fly the plane), navigating using a bubble sextant.
AntarcticPilot
Well-known member
Olds; centimetre accuracy GPS was in routine use in our aircraft in the Antarctic when I retired in 2011, to provide scene centres for aerial photography! And millimetre accuracy has been attainable since the late 1990s using post-processing techniques. Even in the very earliest days of GPS, with Selective Availability and an incomplete constellation we could get centimetre accuracy with a fixed base station and post-processing.
GHA
Well-known member
available to anyone with some bits off aliexpress though?
AntarcticPilot
Well-known member
Well, not quite! But from the later 90s, available to anyone with an internet connection and a GPS that could record phase data.available to anyone with some bits off aliexpress though?
But to get down to centimetre accuracy you need the carrier phase of the signals. I think (memory glitch!) that we used survey quality Trimble equipment.
srm
Well-known member
Sounds like the US Navy's system. Calculated a running fix from the pass of one satellite in polar orbit. Sensitive to the altitude of the satellite, too high or too low and it could not resolve the position. In theory there should have been one usable satellite pass per hour. Very good for ocean passages but not really usable in the swatchways. Commercial instruments used DR between fixes. (I used one of the first in the North Sea, it had an air conditioned four person cabin to house a big rack of electronics). I did wonder about one when the yacht versions first came out but decided that the yacht Decca Navigator sets were better for coastal sailing and Norwegian Sea crossings.
GHA
Well-known member
Did you watch the video? Try from 09:00
