Now as long as Mel is satisfied too then we should be done with the basics of the gps discussion, correct?
I believe that for most of the discussion, we do agree. There are subtle differences to what we are saying, and most of that has distracted us from where we do agree. The only thing I really objected to was when you said that modern receivers don't use more than four satellites.
Very interesting. I have to note that there is disagreement between the first two regarding the maximum number of satellites visible at once. The first link says up to 12, but the second said up to 8, which as far as I know, is the correct number. I was going to work it out mathematically, but honestly, I decided it wasn't important enough to bother with. Possibly the difference comes from the 24 that were first used, and the 32 or so that are supposed to be in place now?
Both articles do say that three satellites can be used for position data in a 2D space, which, again is expected. The forth, which gives greater accuracy by computing the time data errors, also gives the Z position. What we're talking about as to our disagreement, is whether modern receivers are satisfied with using three, or will only work with four or more. I would imagine that now, they will only use four, unless there is some extreme reason not to do so. But for older models, three was common.
This is a cool little animation of position and visibility from a surface point at 45 N, showing a visibility count as a function of time. As I mentioned in an earlier post, it is designed to be at least 8, but is often more.
MStone, I think you still might be missing the relationship between elevation and timing, but it doesn't really matter in the big scheme of things. At least we pretty much agree now.
An Air Force video we posted several months ago. Simple but straightforward.
I believe that for most of the discussion, we do agree. There are subtle differences to what we are saying, and most of that has distracted us from where we do agree. The only thing I really objected to was when you said that modern receivers don't use more than four satellites.
Where was that Mel? I think you misread as that is never a statement I would make.
Water under the bridge in any case and I'll accept your post as an apology and acknowledgement of my correctness.
Kidding Mel. I'd never expect an apology. It was a lively discussion
Also the military version is much more accurate than the public is allowed to receive.
Actually, no. Initially, Selective Availability was used to limit non-military systems to ~100 meters but this was turned off in 2000.
Military grade GPS has better receivers and antennas, can use Selective Availability and are more robust than off-the-shelf or even standard commercial aviation grade. You can get receivers that are just as good. They will cost a LOT and won't have SA but they are just as accurate.
Selective Availability can be re-enabled in the event of war or national emergency.
If you want
Quote:
To limit the accuracy of the public GPS, the satellites respond much less frequently to public devices than to military devices.
GPS satellites do not respond to any GPS receivers (military or civilian) because nothing is transmitted from a GPS receiver.
Receivers that operate above 18Km or faster than 515 meters/second are considered munitions under federal law and are export controlled.
Actually, no. Initially, Selective Availability was used to limit non-military systems to ~100 meters but this was turned off in 2000.
Military grade GPS has better receivers and antennas, can use Selective Availability and are more robust than off-the-shelf or even standard commercial aviation grade. You can get receivers that are just as good. They will cost a LOT and won't have SA but they are just as accurate.
Selective Availability can be re-enabled in the event of war or national emergency.
If you want
GPS satellites do not respond to any GPS receivers (military or civilian) because nothing is transmitted from a GPS receiver.
Receivers that operate above 18Km or faster than 515 meters/second are considered munitions under federal law and are export controlled.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
Block IIR-M (currently 7 satellites) introduced the L2C (civilian) signal.
Also, Wide Area Augmentation System (WAAS) sends correction data.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
I think the P code changed over to the Y code several years ago, but no matter either way as it needs an encryption key at the ground based receiver.
I've never seen any mention of the keyfile being made available for civilian use but can't swear that it hasn't for some specific and highly restricted project.
Well it looks like Trimble may have a couple of high-end commercial navigation and surveying solutions that are able to use the P code with L1/L2 receivers.
Nothing I'd paid all that much attention to, usually focused on consumer-grade devices. Gives me something to read up on now.
How many more links would you like? I've posted at least two professional and gps-industry specific sources as well as listed my own qualifications. I explained the source of your misunderstanding of the Garmin manual. And I've given you a test to prove me wrong.
NOTE: Be sure to read the whole thing, not just the first page. Step 3 and it's explanation of timing is important.
Our posts are crossing each other. I'm not here all the time, which you can see from the times I post. I respond to a post, and sometimes that response comes after another post you made, responding to an earlier post of mine. So you've provided links, in response to my request (finally), and that got posted well after another post you made that didn't have any links that I read, where I requested that you post one.
Our posts are crossing each other. I'm not here all the time, which you can see from the times I post. I respond to a post, and sometimes that response comes after another post you made, responding to an earlier post of mine. So you've provided links, in response to my request (finally), and that got posted well after another post you made that didn't have any links that I read, where I requested that you post one.
I hope that made sense out of it.
Kinda makes sense I guess, but you responded to the links yesterday in post 220. I'm just glad we put that little misunderstanding of the facts behind us.
Comments
You're welcome.
Now as long as Mel is satisfied too then we should be done with the basics of the gps discussion, correct?
Well, except that the Garmin manual is apparently incorrect in light of the 4th being used for timing not elevation.
Edit: After reading the last two posts about vertical errors exceeding horizontal, maybe that is what Garmin is referring to.
You're welcome.
Now as long as Mel is satisfied too then we should be done with the basics of the gps discussion, correct?
I believe that for most of the discussion, we do agree. There are subtle differences to what we are saying, and most of that has distracted us from where we do agree. The only thing I really objected to was when you said that modern receivers don't use more than four satellites.
Well, except that the Garmin manual is apparently incorrect in light of the 4th being used for timing not elevation.
The timing is used for elevation, as well as more accurate positioning on the 2D surface.
Very interesting. I have to note that there is disagreement between the first two regarding the maximum number of satellites visible at once. The first link says up to 12, but the second said up to 8, which as far as I know, is the correct number. I was going to work it out mathematically, but honestly, I decided it wasn't important enough to bother with. Possibly the difference comes from the 24 that were first used, and the 32 or so that are supposed to be in place now?
Both articles do say that three satellites can be used for position data in a 2D space, which, again is expected. The forth, which gives greater accuracy by computing the time data errors, also gives the Z position. What we're talking about as to our disagreement, is whether modern receivers are satisfied with using three, or will only work with four or more. I would imagine that now, they will only use four, unless there is some extreme reason not to do so. But for older models, three was common.
This is a cool little animation of position and visibility from a surface point at 45 N, showing a visibility count as a function of time. As I mentioned in an earlier post, it is designed to be at least 8, but is often more.
http://en.wikipedia.org/wiki/File:ConstellationGPS.gif
An Air Force video we posted several months ago. Simple but straightforward.
http://www.gpsreview.net/air-force-s...how-gps-works/
And one from NASA, who technically has little to do with GPS, but obviously understands it.
http://www.youtube.com/watch?v=DsmvTzw3GP4
Engadget is a cesspool of 14-yr old trolls and fanboys. The click-bait articles the editors post don't help, either.
Correct. And how's this site any different ?
I believe that for most of the discussion, we do agree. There are subtle differences to what we are saying, and most of that has distracted us from where we do agree. The only thing I really objected to was when you said that modern receivers don't use more than four satellites.
Where was that Mel? I think you misread as that is never a statement I would make.
Water under the bridge in any case and I'll accept your post as an apology and acknowledgement of my correctness.
Kidding Mel. I'd never expect an apology. It was a lively discussion
Also the military version is much more accurate than the public is allowed to receive.
Actually, no. Initially, Selective Availability was used to limit non-military systems to ~100 meters but this was turned off in 2000.
Military grade GPS has better receivers and antennas, can use Selective Availability and are more robust than off-the-shelf or even standard commercial aviation grade. You can get receivers that are just as good. They will cost a LOT and won't have SA but they are just as accurate.
Selective Availability can be re-enabled in the event of war or national emergency.
If you want
To limit the accuracy of the public GPS, the satellites respond much less frequently to public devices than to military devices.
GPS satellites do not respond to any GPS receivers (military or civilian) because nothing is transmitted from a GPS receiver.
Receivers that operate above 18Km or faster than 515 meters/second are considered munitions under federal law and are export controlled.
Actually, no. Initially, Selective Availability was used to limit non-military systems to ~100 meters but this was turned off in 2000.
Military grade GPS has better receivers and antennas, can use Selective Availability and are more robust than off-the-shelf or even standard commercial aviation grade. You can get receivers that are just as good. They will cost a LOT and won't have SA but they are just as accurate.
Selective Availability can be re-enabled in the event of war or national emergency.
If you want
GPS satellites do not respond to any GPS receivers (military or civilian) because nothing is transmitted from a GPS receiver.
Receivers that operate above 18Km or faster than 515 meters/second are considered munitions under federal law and are export controlled.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
Block IIR-M (currently 7 satellites) introduced the L2C (civilian) signal.
Also, Wide Area Augmentation System (WAAS) sends correction data.
Even though SA was switched off in 2000, I was unaware that any civilian units are able to use the P code, and thus the L2 frequency, which allows for ionospheric corrections and greater accuracy.
I think the P code changed over to the Y code several years ago, but no matter either way as it needs an encryption key at the ground based receiver.
I've never seen any mention of the keyfile being made available for civilian use but can't swear that it hasn't for some specific and highly restricted project.
Nothing I'd paid all that much attention to, usually focused on consumer-grade devices. Gives me something to read up on now.
http://www.smdc-armyforces.army.mil/...9_NO_3_013.pdf
Here's a good article
http://www.smdc-armyforces.army.mil/...9_NO_3_013.pdf
Thanks. Very informative.
How many more links would you like? I've posted at least two professional and gps-industry specific sources as well as listed my own qualifications. I explained the source of your misunderstanding of the Garmin manual. And I've given you a test to prove me wrong.
I'll try one more time. This one has pictures
http://www.trimble.com/gps/howgps.shtml
NOTE: Be sure to read the whole thing, not just the first page. Step 3 and it's explanation of timing is important.
Our posts are crossing each other. I'm not here all the time, which you can see from the times I post. I respond to a post, and sometimes that response comes after another post you made, responding to an earlier post of mine. So you've provided links, in response to my request (finally), and that got posted well after another post you made that didn't have any links that I read, where I requested that you post one.
I hope that made sense out of it.
Our posts are crossing each other. I'm not here all the time, which you can see from the times I post. I respond to a post, and sometimes that response comes after another post you made, responding to an earlier post of mine. So you've provided links, in response to my request (finally), and that got posted well after another post you made that didn't have any links that I read, where I requested that you post one.
I hope that made sense out of it.
Kinda makes sense I guess, but you responded to the links yesterday in post 220. I'm just glad we put that little misunderstanding of the facts behind us.