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DavidTav
Guest
I must admit I have puzzled over why the boat gps sometimes seems to be 100m or so incorrect, yet the car gps always appears spot on, don't seem to get the car system saying you are in the next street.
Serious GPS question for Airline Pilots
- Thread starter absit_omen
- Start date
grumpy_o_g
Well-Known Member
Car Sat-Nav's have a very detailed and accurate map of the road network built-in. It assumes you're on a road and adjusts any error to put you on the road exactly. If you watch the screen when you diverge from the route you should should be following it will track you along the wrong road for a while then suddenly snap back to the road you are on once it's realised the error is too big. It then recalculates the route and issues a set of increasingly irritating instructions trying to stop you going along the route you want to go.
You can get special "off-road" sat nav's for those who want to drive their cars over Farmer Giles' fields but can't find their way around them.
You can get special "off-road" sat nav's for those who want to drive their cars over Farmer Giles' fields but can't find their way around them.
Leighb
Well-Known Member
It is even more entertaining (infuriating?) if you go onto a road that the TT brain does not know about. It then issues increasingly desperate instructions to "turn around when possible"or "left" or "right" etc etc. Eventually you will re-enter its virtual world and normal service resumes.
The M6 Toll was in this category, as was the A130 from Chelmsford south.
The M6 Toll was in this category, as was the A130 from Chelmsford south.
absit_omen
Well-Known Member
I thought the GPS NOTAM was to alert to the maintenance and non-availability of, perhaps, just one satellite for a specific time period. This, presumably, enables users to employ alternative navigation methods.
What I find difficult to accept is the 'military' not only having the power to disable an entire system at will but persisting in trying it out on a regular basis! The notion that they are 'practicing on exercise' is as alien to me as launching a trident missile with warhead just to make sure it still works.
If the 'military' already know they can disable GPS why keep on practising it? Or do they just like stirring us up and giving us our own war stories to tell at the bar!
"Bravo one zero - target in sight, AWB, four pax, nervous skipper"
"Bravo two zero - Roger, wait for him to close on the rocks"
"Bravo one zero - heading for rocks, in fog bank now. Skipper up and down from chart table like a YoYo. SWMBO now involved, VERY raised voices"
"Bravo two zero - Roger, wait for the sweat beads to appear"
"Bravo one zero - sweat now, bowel movement imminent"
"Bravo two zero - OK give to them. SWITCH OFF NOW!!!!!!
Blast them with an EMP whilst you are at it - that should screw things up!!!"
"Bravo one zero - HAHAHAHAHAHAHA - better than that lot yeserday! - Out
/forums/images/graemlins/wink.gif
Only joking Lemain - I take your point.
What I find difficult to accept is the 'military' not only having the power to disable an entire system at will but persisting in trying it out on a regular basis! The notion that they are 'practicing on exercise' is as alien to me as launching a trident missile with warhead just to make sure it still works.
If the 'military' already know they can disable GPS why keep on practising it? Or do they just like stirring us up and giving us our own war stories to tell at the bar!
"Bravo one zero - target in sight, AWB, four pax, nervous skipper"
"Bravo two zero - Roger, wait for him to close on the rocks"
"Bravo one zero - heading for rocks, in fog bank now. Skipper up and down from chart table like a YoYo. SWMBO now involved, VERY raised voices"
"Bravo two zero - Roger, wait for the sweat beads to appear"
"Bravo one zero - sweat now, bowel movement imminent"
"Bravo two zero - OK give to them. SWITCH OFF NOW!!!!!!
Blast them with an EMP whilst you are at it - that should screw things up!!!"
"Bravo one zero - HAHAHAHAHAHAHA - better than that lot yeserday! - Out
/forums/images/graemlins/wink.gif
Only joking Lemain - I take your point.
BrendanS
Well-Known Member
One satellite down is going to make no difference to most people, as there will still be multiple satellites in line of sight and available to give accurate location.
absit_omen
Well-Known Member
I agree with you that one out of the system should not make any difference. However, why this which was extracted from a NOTAM:?
Here are two GPS NOTAMs that showed up today indicating satellite #6 is out of service and #3 will be out of service on July 17 from 1600 to 2230 Zulu:
GPS 06/040 GPS PRN 6 OTS
GPS 07/009 GPS PRN 3 OTS WEF 0607171600-0607172230
Clearly the absence of just one Sat over a period of time merits an inclusion on a NOTAM.
Here are two GPS NOTAMs that showed up today indicating satellite #6 is out of service and #3 will be out of service on July 17 from 1600 to 2230 Zulu:
GPS 06/040 GPS PRN 6 OTS
GPS 07/009 GPS PRN 3 OTS WEF 0607171600-0607172230
Clearly the absence of just one Sat over a period of time merits an inclusion on a NOTAM.
BrendanS
Well-Known Member
It's just a notification, it makes no actual difference to most people unless you are in an area where you receive only a very few satellites, which is why they give the warning.
Professional users also need to be notified of downtime, if they are doing tests etc.
Professional users also need to be notified of downtime, if they are doing tests etc.
absit_omen
Well-Known Member
OK, thanks.
Sounds like a good job writing GPS NOTAMS. Those (probably hayseeds) who are affected probably won't notice as their coverage is usually crap anyway. The others (Southerners) won't notice as they have more satellites than debenture seats at Twickenham and losing one at a time won't make a jot of difference. They will just buy a shed load more with the next bonus!
Time for bed. Now, where are the co-ordinates?
Sounds like a good job writing GPS NOTAMS. Those (probably hayseeds) who are affected probably won't notice as their coverage is usually crap anyway. The others (Southerners) won't notice as they have more satellites than debenture seats at Twickenham and losing one at a time won't make a jot of difference. They will just buy a shed load more with the next bonus!
Time for bed. Now, where are the co-ordinates?
bilbobaggins
N/A
As a once-upon-a-time military nav specialist, and who's involvement with the Royal Institute of Navigation dates back to 1970, 'Leesen verree carefuleee! I vill zay ziss onlee wunce!"
The present NavStar/GPS facility was designed, built, maintained and paid-for by the US Department of Defence - and still is. It was and remains a military system. It has a military purpose and function. That was, originally, to augment the TERRCOM guidance system of the first generation of cruise missiles. The fact that we others are able to - and permitted to - use as a freebie one crude transmitted function, the Course Acquisition Signal, is an excellent bonus.
As with all developments in the use of radio navigation systems usable by the military, no sooner had the US deployed the GPS constellation in orbit than several potential adversaries started to develop counter-measures. And also quite a few 'friendly' states, too. One can buy examples of such 'signal disruptors' at military trade shows. Then there were counter-counter-measures, in the wholly normal life-cycle of such guidance navaids. That should surprise no-one.
Today, probably all high-value surface combatants - and quite a few vessels one would consider non-combatant - worldwide will have GPS 'signal disruptors' of various forms installed as part of their defensive suite. Those systems need regular 'tyre checks' for continued function, perhaps daily, and any new swop-out boxes also need to be run up and proven to work 'as it says on the tin'. One should not be in the least bit surprised at the intermittent and unadvertised degradation of signal, and subsequent signal processing, in the broad vicinity of any naval facilities.
Galileo will be different, but there will certainly be similar 'safeguards'.....
/forums/images/graemlins/grin.gif
And for MM5AHO....
Geoff, I, too have sailed through the Corrievreckan in a Rival - at dead nominal slack and W to E ( for there are no old, bold navigators ) and, yes, there were brief occasions when we were going backwards, but those were when the residual 'swirlies' took firm hold of the keel. I wouldn't want to be there in the dark, half-spring tide rise, with a westerly wind and swell running.
/forums/images/graemlins/wink.gif
The present NavStar/GPS facility was designed, built, maintained and paid-for by the US Department of Defence - and still is. It was and remains a military system. It has a military purpose and function. That was, originally, to augment the TERRCOM guidance system of the first generation of cruise missiles. The fact that we others are able to - and permitted to - use as a freebie one crude transmitted function, the Course Acquisition Signal, is an excellent bonus.
As with all developments in the use of radio navigation systems usable by the military, no sooner had the US deployed the GPS constellation in orbit than several potential adversaries started to develop counter-measures. And also quite a few 'friendly' states, too. One can buy examples of such 'signal disruptors' at military trade shows. Then there were counter-counter-measures, in the wholly normal life-cycle of such guidance navaids. That should surprise no-one.
Today, probably all high-value surface combatants - and quite a few vessels one would consider non-combatant - worldwide will have GPS 'signal disruptors' of various forms installed as part of their defensive suite. Those systems need regular 'tyre checks' for continued function, perhaps daily, and any new swop-out boxes also need to be run up and proven to work 'as it says on the tin'. One should not be in the least bit surprised at the intermittent and unadvertised degradation of signal, and subsequent signal processing, in the broad vicinity of any naval facilities.
Galileo will be different, but there will certainly be similar 'safeguards'.....
/forums/images/graemlins/grin.gif
And for MM5AHO....
Geoff, I, too have sailed through the Corrievreckan in a Rival - at dead nominal slack and W to E ( for there are no old, bold navigators ) and, yes, there were brief occasions when we were going backwards, but those were when the residual 'swirlies' took firm hold of the keel. I wouldn't want to be there in the dark, half-spring tide rise, with a westerly wind and swell running.
/forums/images/graemlins/wink.gif