If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
"Brad" wrote in message ups.com... In an airplane, your immediate surroundings should have no bearing on your GPS accuracy unless you're flying under bridges, trees, through tunnels...you get the idea. Keep in mind that the GPS constellation is constantly moving so there are no dead areas, like you might have with a VOR signal. I'm not sure what you mean by deteriorating conditions...how is your meter going to predict ionospheric activity or a satellite going off line? It's not like bars on a cell phone. For non-FAA rated GPS devices, it's not hard to get a bad GPS signal that is highly inaccurate. It's not always the case that you just get a signal failure or a good signal. Some of these GPS antennas are getting extremely good at giving you a reading in spite of a bad positioning that blocks important parts of the sky. Regarding standards for handheld GPS, who would enforce the standards? What if a particular receiver did meet the standards? Given some number of satellites, each with a given signal quality, I think any GPS software could make statistical calculations that would result in two numbers for number of feet of horizontal and vertical accuracy, to some confidence interval. How do you guarantee that the author of the software does the math correctly? I guess you can't except by cross reference to other devices. But the same complaint could be made about any other part of the software. How do you know he converted spacial coordinates from the GPS to a correct map position? No doubt there could be errors in the implementation of those algorithms, as with any other algorithm. -- Will |
#22
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
"Sam Spade" wrote in message
news:l8n3g.174223$bm6.98713@fed1read04... I got an interesting lesson in GPS recently while traveling with a handheld GPS as the passenger in a plane. The GPS showed us landing about two miles east of the airport. I figured out only later that the position of the antenna was such that many satellites were blocked, so the accuracy of the GPS signal was greatly diminished. That large of an error was probably due to the substantial altitude change of the airliner while your GPS was staggering along in 2-D mode. I think the reason may have been that most satellites were blocked inside the cockpit. But why would anyone object to this non-FAA software simply self-reporting that its current accuracy was some huge number of horizontal and vertical feet (i.e., that it was not currently very accurate)? I cannot understand why anyone would feel that this is a bad thing to tell a user of that device. If you don't want the information then ignore it. airliner. Some owners, who are savvy on this still, install an external antenna on their aircraft for their hand-held GPS. It will never have the problems you experienced with an external antenna. That's a great idea. Maybe more handheld GPS users would become aware of the need for for an external antenna if their GPS software clearly communicated when the signals they are getting are not very accurate? That fact might inspire more users of these devices to understand that antenna placement is quite critical for these devices. -- Will |
#23
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
Will wrote:
"John Theune" wrote in message news:Udo3g.5009$bU6.3635@trnddc06... I'm somewhat surprised that no one has mentioned that both the Garmin and Lowrance units that I'm familiar with have a page for satelitte signal strength. I've never felt the need to run thru the 430/530 pages to find a similar page but would not be surprised to find it buried in there somewhere. To answer the OP's question it's there you just need to read the manual to find which sub-menu it's on. If he's using a non-aviation unit then all bets are off but again I would think it would be there somewhere. Also on the units I use regularly the airplane icon flashs on the main display when the signal is lost ala a pseudo RAIM indicator You are right all GPS software usually implements a satellite signal page. It's not in any way shape or form what I asked for. I want the GPS to take all of the inputs for number of satellites and signal strength and derive from that just two integers: 1) Number of feet/meters of horizontal accuracy, within some confidence interval (e.g., 99.95%) 2) Number of feet/meters of vertical accuracy, within some confidence interval (e.g., 99.95%) Those two numbers could become optional numbers for the primary display. No one is forcing anyone to use them. If you want to simply trust the instrument to give you a go-nogo decision, it's your life and if you feel that is safe it's a free world (as long as you follow FAA rules ) so be my guest. For my personal taste, I understand that a GPS display is always an illusion subject to different levels of inaccuracy. I am sensitive to the difference between a display that is showing me accuracy to 10 ft, 100 ft, or 1000 ft. In the original posted example the GPS was off target by more than 5000 ft. Nothing on the original display gave me any clue that this was the case. The two numbers I am asking for would communicate quite succinctly that no one should rely on the display for anything other than the most gross kind of positioning. While I would love to see the feature I am looking for in any FAA-compliant instrument like a Garmin 530, I think the feature becomes most critical in non-FAA compliant GPS devices/software. The authors of such packages cannot control the quality of the satellite antenna, or mounting, and substandard GPS reception is probably a routine thing for PDA based GPS devices/software. So finding a succinct way to communicate the accuracy of the current signal in numbers that mean something to any user becomes quite important. Making people look at satellite maps and signal strength seems like a pure engineering exercise, and it doesn't collapse the input data into a useful form. And right on that same page for the Lowrance unit is the EPE ( Estimated Probability of Error ) in feet for the current location. The EPE is for horizontal accuracy as the vertical accuracy is mostly meaningless for GPS as they can only give you vertical guidance from a perfect sphere and the earth does not quite fit that. vertical accuracy would require the GPS to have a complete model of the earth elevation and coralate that to the horizontal location so as to determine the actual vertical location vs calculated position. Now I spent a few moments messing with my unit and found that I can place the EPE on the main map page along side course, heading , speed and so forth. If you want to know more I suggest you look at the manual for your system. |
#24
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
But why would anyone object to this non-FAA software simply
self-reporting that its current accuracy was some huge number of horizontal and vertical feet (i.e., that it was not currently very accurate)? Because it's a source of more bugs. Jose -- The price of freedom is... well... freedom. for Email, make the obvious change in the address. |
#25
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
Read the TSO and then read the description of RAIM other
accuracy monitoring software built into the unit. -- James H. Macklin ATP,CFI,A&P "Will" wrote in message ... | | "John Theune" wrote in message | news:Udo3g.5009$bU6.3635@trnddc06... | I'm somewhat surprised that no one has mentioned that both the Garmin | and Lowrance units that I'm familiar with have a page for satelitte | signal strength. I've never felt the need to run thru the 430/530 pages | to find a similar page but would not be surprised to find it buried in | there somewhere. To answer the OP's question it's there you just need | to read the manual to find which sub-menu it's on. If he's using a | non-aviation unit then all bets are off but again I would think it would | be there somewhere. Also on the units I use regularly the airplane icon | flashs on the main display when the signal is lost ala a pseudo RAIM | indicator | | You are right all GPS software usually implements a satellite signal page. | It's not in any way shape or form what I asked for. | | I want the GPS to take all of the inputs for number of satellites and signal | strength and derive from that just two integers: | | 1) Number of feet/meters of horizontal accuracy, within some confidence | interval (e.g., 99.95%) | | 2) Number of feet/meters of vertical accuracy, within some confidence | interval (e.g., 99.95%) | | Those two numbers could become optional numbers for the primary display. | No one is forcing anyone to use them. If you want to simply trust the | instrument to give you a go-nogo decision, it's your life and if you feel | that is safe it's a free world (as long as you follow FAA rules ) so be | my guest. | | For my personal taste, I understand that a GPS display is always an illusion | subject to different levels of inaccuracy. I am sensitive to the | difference between a display that is showing me accuracy to 10 ft, 100 ft, | or 1000 ft. In the original posted example the GPS was off target by more | than 5000 ft. Nothing on the original display gave me any clue that this | was the case. The two numbers I am asking for would communicate quite | succinctly that no one should rely on the display for anything other than | the most gross kind of positioning. | | While I would love to see the feature I am looking for in any FAA-compliant | instrument like a Garmin 530, I think the feature becomes most critical in | non-FAA compliant GPS devices/software. The authors of such packages | cannot control the quality of the satellite antenna, or mounting, and | substandard GPS reception is probably a routine thing for PDA based GPS | devices/software. So finding a succinct way to communicate the accuracy of | the current signal in numbers that mean something to any user becomes quite | important. Making people look at satellite maps and signal strength seems | like a pure engineering exercise, and it doesn't collapse the input data | into a useful form. | | -- | Will | | | | |
#26
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
And it could double the cost of the system for no useful
purpose. I'm sure that if anybody wanted a custom made GPS unit, Garmin or some other company would be happy to take your million dollars and build you one or even two of them. -- James H. Macklin ATP,CFI,A&P -- The people think the Constitution protects their rights; But government sees it as an obstacle to be overcome. some support http://www.usdoj.gov/olc/secondamendment2.htm See http://www.fija.org/ more about your rights and duties. "Jose" wrote in message . com... | But why would anyone object to this non-FAA software simply | self-reporting that its current accuracy was some huge number of horizontal | and vertical feet (i.e., that it was not currently very accurate)? | | Because it's a source of more bugs. | | Jose | -- | The price of freedom is... well... freedom. | for Email, make the obvious change in the address. |
#27
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
You will never get the display you are looking for in a handheld device.
IMHO handhelds will never have RAIM. Bob Gardner "Will" wrote in message ... "John Theune" wrote in message news:Udo3g.5009$bU6.3635@trnddc06... I'm somewhat surprised that no one has mentioned that both the Garmin and Lowrance units that I'm familiar with have a page for satelitte signal strength. I've never felt the need to run thru the 430/530 pages to find a similar page but would not be surprised to find it buried in there somewhere. To answer the OP's question it's there you just need to read the manual to find which sub-menu it's on. If he's using a non-aviation unit then all bets are off but again I would think it would be there somewhere. Also on the units I use regularly the airplane icon flashs on the main display when the signal is lost ala a pseudo RAIM indicator You are right all GPS software usually implements a satellite signal page. It's not in any way shape or form what I asked for. I want the GPS to take all of the inputs for number of satellites and signal strength and derive from that just two integers: 1) Number of feet/meters of horizontal accuracy, within some confidence interval (e.g., 99.95%) 2) Number of feet/meters of vertical accuracy, within some confidence interval (e.g., 99.95%) Those two numbers could become optional numbers for the primary display. No one is forcing anyone to use them. If you want to simply trust the instrument to give you a go-nogo decision, it's your life and if you feel that is safe it's a free world (as long as you follow FAA rules ) so be my guest. For my personal taste, I understand that a GPS display is always an illusion subject to different levels of inaccuracy. I am sensitive to the difference between a display that is showing me accuracy to 10 ft, 100 ft, or 1000 ft. In the original posted example the GPS was off target by more than 5000 ft. Nothing on the original display gave me any clue that this was the case. The two numbers I am asking for would communicate quite succinctly that no one should rely on the display for anything other than the most gross kind of positioning. While I would love to see the feature I am looking for in any FAA-compliant instrument like a Garmin 530, I think the feature becomes most critical in non-FAA compliant GPS devices/software. The authors of such packages cannot control the quality of the satellite antenna, or mounting, and substandard GPS reception is probably a routine thing for PDA based GPS devices/software. So finding a succinct way to communicate the accuracy of the current signal in numbers that mean something to any user becomes quite important. Making people look at satellite maps and signal strength seems like a pure engineering exercise, and it doesn't collapse the input data into a useful form. -- Will |
#28
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
As the lawyers like to say in court "evidence not in the record." There
is no proof at all for the claim that some straightforward math calculations in any GPS software is going to to double the cost of the GPS. What I was describing doesn't require any new hardware, and it's just a matter of calculating some accuracy numbers and representing them in the standard UI. If it prevents one death that results in a multi-million dollar lawsuit, it would payback the one man-month of work it might take to do those calculations in software 100 fold or more. -- Will "Jim Macklin" wrote in message news:4bx3g.8797$ZW3.1447@dukeread04... And it could double the cost of the system for no useful purpose. I'm sure that if anybody wanted a custom made GPS unit, Garmin or some other company would be happy to take your million dollars and build you one or even two of them. -- James H. Macklin ATP,CFI,A&P |
#29
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
Will wrote:
As the lawyers like to say in court "evidence not in the record." There is no proof at all for the claim that some straightforward math calculations in any GPS software is going to to double the cost of the GPS. What I was describing doesn't require any new hardware, and it's just a matter of calculating some accuracy numbers and representing them in the standard UI. If it prevents one death that results in a multi-million dollar lawsuit, it would payback the one man-month of work it might take to do those calculations in software 100 fold or more. How would the use of the GPS be responsible for someone's death? For VFR work, handeld or otherwise, GPS is an advisory system only, and not guaranteed. User beware. Have alternative nav sources, like people did for decades before GPS came on the scene. Did you read the dislaimers on your GPS's packaging when you got it? Didn't read em? Too bad.. Didn't buy it new and have the original packaging? Still your problem. And being in VFR.. you shouldnt have to worry about conditions bad enough to require an approach. For IFR work, either you have a good signal, or you do NOT have a good signal (as calculated by your reciever, and displayed in the form of a RAIM integrity warning). No shades of gray here. Based on the past few days worth of posts.. I'm guessing you haven't done much in the way of actual IFR approaches to minimums.. and I am also predicting you've not done any of it behind IFR approved GPS devices, after having thoroughly read the manual and recieved training in such... workload and workload reduction is crucial. What you propose is to add workload, unnecesarily, to give quanititative data (percentage points/errors) regarding something that is already addressed in a qualitative manner (RAIM OK or NOT OK). Now you try to justify its cost/benefit by a hypothetical lawsuit over the lack of something that is not mandated, not needed and not justified? Sorry... doesn't add up. Dave |
#30
|
|||
|
|||
Accuracy of GPS in Garmin 430/530
Well you get a real-time calculated number in the horizontal direction,
http://www.garmin.com/manuals/GNS430_PilotsGuide.pdf pages 44, 46 and http://www.garmin.com/manuals/GNS530_PilotsGuide.pdf page 43 Garmin calculates the Estimated Position Error (in feet or meters horizontally), but does not present an estimate of the vertical error. I believe Garmin has done this on most if not all of their aviation units, handheld and panel mount. I've got an old GPS95XL and it does the same thing. Regards, John Severyn @KLVK "Will" wrote in message ... Is there any way to have the Garmin 430/530 put its current display accuracy on the primary display as an ongoing statistic, based on the number of satellites in view? How, in general, do the Garmin units notify you of situations where GPS accuracy has been compromised to a level that makes it unsafe to use the Garmin for a GPS approach? I got an interesting lesson in GPS recently while traveling with a handheld GPS as the passenger in a plane. The GPS showed us landing about two miles east of the airport. I figured out only later that the position of the antenna was such that many satellites were blocked, so the accuracy of the GPS signal was greatly diminished. The particular software I was using didn't display its current accuracy on the primary display. Based on that event, I realize I cannot just trust a GPS display without first understanding the current accuracy of the signal. What would be really nice is if the primary display would show vertical and horizontal accuracy as two separate numbers, based on some high confidence interval (99.99+%). Knowing that the current display reading is accurate to 10 ft vertical and 15 ft horizontal, for example, might make you a lot more comfortable in following a GPS approach than a display where the 99.99% confidence interval is 2000 ft vertical/horizontal (i.e., GPS reliability is completely compromised by virtue of blocked satellites, bad GPS antenna, etc). -- Will |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Garmin backing away from additional GDL-69 features for 430/530 products? | Andrew Gideon | Owning | 2 | September 9th 05 11:36 PM |
Inexpensive Garmin 430/530 question | vlado | Owning | 2 | May 19th 05 03:21 AM |
Pirep: Garmin GPSMAP 296 versus 295. (very long) | Jon Woellhaf | Piloting | 12 | September 4th 04 11:55 PM |
WAAS and Garmin 430/530 | DoodyButch | Owning | 23 | October 13th 03 04:06 AM |
Garmin 430/530 Questions | Steve Coleman | Instrument Flight Rules | 16 | August 28th 03 09:04 PM |