Kerry.

About 110' Cheers, Kerry. I never get lost everybody keeps telling me where to go

PDOP & HDOP are different with HDOP being less than PDOP. The SPS specifications require a PDOP of 6 or less but that's also in conjunction with some other system conditions and constraints. Cheers, Kerry. I never get lost everybody keeps telling me where to go

PDOP & HDOP are different with HDOP being less than PDOP. The SPS specifications require a PDOP of 6 or less but that's also in conjunction with some other system conditions and constraints. Cheers, Kerry. I never get lost everybody keeps telling me where to go

MrG, yeah I saw you were on the ball just needed to head off what appears to be some mis-conceptions. As I've said else where without the underground surveys being right the whole ending might have been totally different. The end result was ONLY ever going to be as good as the underground information available. That's one of the problems with some of this equipment one can "teach" anyone how to push buttons but the real requirement is in "knowing" the mechanics Cheers, Kerry. I never get lost everybody keeps telling me where to go

MrG, yeah I saw you were on the ball just needed to head off what appears to be some mis-conceptions. As I've said else where without the underground surveys being right the whole ending might have been totally different. The end result was ONLY ever going to be as good as the underground information available. That's one of the problems with some of this equipment one can "teach" anyone how to push buttons but the real requirement is in "knowing" the mechanics Cheers, Kerry. I never get lost everybody keeps telling me where to go

Hate to burst anybodies bubble but that's really only half the story. That gear pictured "by it self" is basically not all that much more accurate than any standard SPS type reciever. There's much more to things than one simply sees pictured as without it's mate or other reference hardware it really doesn't do all that much. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Hate to burst anybodies bubble but that's really only half the story. That gear pictured "by it self" is basically not all that much more accurate than any standard SPS type reciever. There's much more to things than one simply sees pictured as without it's mate or other reference hardware it really doesn't do all that much. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Integrity, yes much more to do with integrity and safety-of-life type issues than purely accuarcy. It's all about "knowing" what the accuracy should be with appropriate warnings when outside limits. I believe the current aviation guidelines in the U.S requires reception of warnings in 6 seconds or less (any pilots?). WAAS takes 5 seconds to process and broadcast the data from 27 ground stations so things are fairly tight. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Integrity, yes much more to do with integrity and safety-of-life type issues than purely accuarcy. It's all about "knowing" what the accuracy should be with appropriate warnings when outside limits. I believe the current aviation guidelines in the U.S requires reception of warnings in 6 seconds or less (any pilots?). WAAS takes 5 seconds to process and broadcast the data from 27 ground stations so things are fairly tight. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, just a quick one with the time or more imortantly the timing. The internal time in all receivers is basically just to tell the time. The actual timing is one of the computed unknowns in the position solution. That why one needs a minimum of 3 sats for a 2D solution to calculate the 3 unknowns (XY & Time), similer with a 3D solution requires a min of 4 sats to calc XYZ & time. Very simple soultion to a complex problem and certainly keeps the cost of receivers to a minimum. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, just a quick one with the time or more imortantly the timing. The internal time in all receivers is basically just to tell the time. The actual timing is one of the computed unknowns in the position solution. That why one needs a minimum of 3 sats for a 2D solution to calculate the 3 unknowns (XY & Time), similer with a 3D solution requires a min of 4 sats to calc XYZ & time. Very simple soultion to a complex problem and certainly keeps the cost of receivers to a minimum. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, I knew it wouldn't but the whole point was the advertising material suggested it would . The only way to argue with sales/marketing people when certain companies are paying their salary is to throw "facts" at them. But for sure things are becoming much clearer these days but it's still interesting what the WAAS signal does to the navigation for those that might be on the fringe of useability. Up until recently there's simply been too much hype regarding WAAS, EGNOS and MSAS. Testing EPE up against a cliff, obstructed data, no problem I can give you that too based on the following data http://www.cqnet.com.au/~user/aitken/gps/gps_obs.htm As for dual frequency your basically on the right line but no not really similar to WAAS as WAAS is a third party augmentation (and a dadgum expensive augmentation at that) like DGPS and others where as the second GPS frequency is part and parcel of the GPS system proper. With 2 frequencies one of the biggest errors in the atmospherics can be reduced based on the actual data instead of the current modelled atmospheric corrections that are used with standalone single freq receivers. With 2 frequencies then Wide Area Differential GPS (such as WAAS) goes up another level as well. Elevation from GPS is really only a guide anyway at the vertical component is about 2.5 times less accurate than the horizontal and relies on internal geoid models which for a handheld is quite sparse and approximate to cover the entire world. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, I knew it wouldn't but the whole point was the advertising material suggested it would . The only way to argue with sales/marketing people when certain companies are paying their salary is to throw "facts" at them. But for sure things are becoming much clearer these days but it's still interesting what the WAAS signal does to the navigation for those that might be on the fringe of useability. Up until recently there's simply been too much hype regarding WAAS, EGNOS and MSAS. Testing EPE up against a cliff, obstructed data, no problem I can give you that too based on the following data http://www.cqnet.com.au/~user/aitken/gps/gps_obs.htm As for dual frequency your basically on the right line but no not really similar to WAAS as WAAS is a third party augmentation (and a dadgum expensive augmentation at that) like DGPS and others where as the second GPS frequency is part and parcel of the GPS system proper. With 2 frequencies one of the biggest errors in the atmospherics can be reduced based on the actual data instead of the current modelled atmospheric corrections that are used with standalone single freq receivers. With 2 frequencies then Wide Area Differential GPS (such as WAAS) goes up another level as well. Elevation from GPS is really only a guide anyway at the vertical component is about 2.5 times less accurate than the horizontal and relies on internal geoid models which for a handheld is quite sparse and approximate to cover the entire world. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by fizzymagic:In other words, you intentionally did a test of WAAS that was invalid. And you wanted to prove what? Geez. When I said that every test I knew of using WAAS showed improved accuracy, I assumed that people would understand that I meant every _valid_ test. Your test is the intellectual equivalent of claiming a Ferrari is a worthless car because you tested in on a 4WD-only road and it got stuck. Now I did spell out what this was all about, nothing to do with accuracy but all to do with EPE and knowing or not knowing and in that regard what better way to do that. One other point was that wasn't mentioned was this was originally done in response to some rather deceptive advertising in pushing WAAS (and it's pin point accuracy) in areas that it was never going to work. You can talk about every_valid_test but some of the advertising hype I've seen (and questioned) is simply that advertising hype with no substance from manufacturers who should know better. Now if Ferrari made claims they could do what a 4WD does then you'd obviously want to test that wouldn't you Lets face it certain manufacturers were still comparing WAAS to SPS accuarcy pre Selective Availability almost 2 years after SA was set to zero but at least that's now been changed to the real world. So for a standard SPS receiever with a CEP of 1.8m (< 6') what does 6 billion dollars worth of augmentation [WAAS) do for the average recreational user considering that 6 billion dollars only services a smallish part of the world compared to GPS proper. There's starting to be a very fine line these days where reality begins and ends. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by fizzymagic:In other words, you intentionally did a test of WAAS that was invalid. And you wanted to prove what? Geez. When I said that every test I knew of using WAAS showed improved accuracy, I assumed that people would understand that I meant every _valid_ test. Your test is the intellectual equivalent of claiming a Ferrari is a worthless car because you tested in on a 4WD-only road and it got stuck. Now I did spell out what this was all about, nothing to do with accuracy but all to do with EPE and knowing or not knowing and in that regard what better way to do that. One other point was that wasn't mentioned was this was originally done in response to some rather deceptive advertising in pushing WAAS (and it's pin point accuracy) in areas that it was never going to work. You can talk about every_valid_test but some of the advertising hype I've seen (and questioned) is simply that advertising hype with no substance from manufacturers who should know better. Now if Ferrari made claims they could do what a 4WD does then you'd obviously want to test that wouldn't you Lets face it certain manufacturers were still comparing WAAS to SPS accuarcy pre Selective Availability almost 2 years after SA was set to zero but at least that's now been changed to the real world. So for a standard SPS receiever with a CEP of 1.8m (< 6') what does 6 billion dollars worth of augmentation [WAAS) do for the average recreational user considering that 6 billion dollars only services a smallish part of the world compared to GPS proper. There's starting to be a very fine line these days where reality begins and ends. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by fizzymagic: So your claim that WAAS is useless on handlheld devices because they don't have centimeter accuracy is demonstrably incorrect. No WAAS isn't all that it's made out to be especially in an environment it was never really intended and it has nothing to do with cm accuracy. One thing for sure these days there is no where near a US$6 billion improvment in accuracy. For a lot less than that amount of $$'s some more current generation sats and our coming second cival frequency will give more to many more users. The problem with getting new generation sats is the old ones appear to have been built too well and won't die quick enough Anyway getting off the subject The view that WAAS was never really intended for land based activities with obstructive environments is (now) basically universally accepted. To reduce the obstruction effects on especially the L1 WAAS frequency relying on a handheld with something like a patch antenna is at times expecting a little too much considering the requirements, constraints and possible conditions. I also wouldn’t limit WAAS’s distractions to simply handhelds either but handhelds have more limitations than some fixed mount units. It’s only in recent times that much of the WAAS hype has been sorted out a little better and things better clarified. However there’s really more important things to WAAS than simply accuracy but recreational users really aren’t interested in those features and besides the receivers generally don’t have the software capability to optimize these benefits. The following was done (deliberately) outside the ground station network for several reasons. 1) just to see what the "effects" would be and 2) to compare actual error (in the real world) to estimated error (EPE etc) for both standard GPS and the "affects" of just the WAAS carrier. In both instances both the same receiver (recreational type) recorded over 23 hours on a well defined reference point. Standard (real world) GPS accuracy was 1.8m (CEP), 2.4m (RMS) & 4m @ 95%. The receivers estimated position in comparison did not show less than 3.5m with 4.4m (CEP) and 5.0m 95% of the time. The estimated error was certainly very conservative but didn’t really reflect the real world. Strange the lowest value was 3.5m? Based on the WAAS "received signal" the "affected" accuracy was 20.1m (CEP), 27.6m (RMS) and 87.3m @ 95%. The unit’s estimated errors were 100.5m (CEP), 133.7m (RMS) and simply heaps at 95% (max was just over 1km) which didn’t even come close to the real world as far as the unit knowing where it was or even thought it was. Obviously this isn't true WAAS accuarcy (as such) but does highlight was can happen when things go of the rails. Visually, reality looked something like this everybody keeps telling me where to go

quote:Originally posted by fizzymagic: So your claim that WAAS is useless on handlheld devices because they don't have centimeter accuracy is demonstrably incorrect. No WAAS isn't all that it's made out to be especially in an environment it was never really intended and it has nothing to do with cm accuracy. One thing for sure these days there is no where near a US$6 billion improvment in accuracy. For a lot less than that amount of $$'s some more current generation sats and our coming second cival frequency will give more to many more users. The problem with getting new generation sats is the old ones appear to have been built too well and won't die quick enough Anyway getting off the subject The view that WAAS was never really intended for land based activities with obstructive environments is (now) basically universally accepted. To reduce the obstruction effects on especially the L1 WAAS frequency relying on a handheld with something like a patch antenna is at times expecting a little too much considering the requirements, constraints and possible conditions. I also wouldn’t limit WAAS’s distractions to simply handhelds either but handhelds have more limitations than some fixed mount units. It’s only in recent times that much of the WAAS hype has been sorted out a little better and things better clarified. However there’s really more important things to WAAS than simply accuracy but recreational users really aren’t interested in those features and besides the receivers generally don’t have the software capability to optimize these benefits. The following was done (deliberately) outside the ground station network for several reasons. 1) just to see what the "effects" would be and 2) to compare actual error (in the real world) to estimated error (EPE etc) for both standard GPS and the "affects" of just the WAAS carrier. In both instances both the same receiver (recreational type) recorded over 23 hours on a well defined reference point. Standard (real world) GPS accuracy was 1.8m (CEP), 2.4m (RMS) & 4m @ 95%. The receivers estimated position in comparison did not show less than 3.5m with 4.4m (CEP) and 5.0m 95% of the time. The estimated error was certainly very conservative but didn’t really reflect the real world. Strange the lowest value was 3.5m? Based on the WAAS "received signal" the "affected" accuracy was 20.1m (CEP), 27.6m (RMS) and 87.3m @ 95%. The unit’s estimated errors were 100.5m (CEP), 133.7m (RMS) and simply heaps at 95% (max was just over 1km) which didn’t even come close to the real world as far as the unit knowing where it was or even thought it was. Obviously this isn't true WAAS accuarcy (as such) but does highlight was can happen when things go of the rails. Visually, reality looked something like this everybody keeps telling me where to go

EraSeek, gotta look for some data for Fizzymagic but these are easy ones. SIS (Signal-In-Space) which accuracy is now based on, basically without the added "affects" that the user is responsible for managing. The system operators only control the signal at the satellite level and really have no control of some of the uncontrollables like atmospherics and yes "users". CEP (Circular Error Probable) the radius of a circle within which contains 50% of the horizontal positions. SEP is (Spherical Error Probable) which is similar but is the radius of a sphere which relate to 50% of 3D positions. The channel myth is that a 12 channel receiver is more accurate than a 10 or 9 or 8 or 6 or 5 etc considering things like satellite geometry etc. That is not so as really if receivers were configurable (or configured correctly) then one would mask out the low horizon satellites, which are the ones that can tend to decrease the accuracy. Some manufacturers actually do this as a fixed setting but others don't and will accept all satellites (regardless) right down to the horizon. There is a point to useable channels but really to the sales/marketing people more sounds better. Accuracy has little to do with the number of satellites (hence channels) and all to do with geometry. Really the full 12 channels are used only a small % of the time but right now we have an overpopulated system (28) so we are a little spoilt. WAAS is different but the 1 or 2 channels that WAAS uses is really irrelevent to the result. Similar with DGPS as there are only corrections transmitted for 9 satellites and the same satellites must be in view at both locations for corrections to be applied. But to cut a long story short the "original" design was for a 11+1 but somebody got things wrong so everybody followed. Now would you have brought a 11+1 channel receiver if the opposition made a 12 Averaging certainly does very little for me these days. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, gotta look for some data for Fizzymagic but these are easy ones. SIS (Signal-In-Space) which accuracy is now based on, basically without the added "affects" that the user is responsible for managing. The system operators only control the signal at the satellite level and really have no control of some of the uncontrollables like atmospherics and yes "users". CEP (Circular Error Probable) the radius of a circle within which contains 50% of the horizontal positions. SEP is (Spherical Error Probable) which is similar but is the radius of a sphere which relate to 50% of 3D positions. The channel myth is that a 12 channel receiver is more accurate than a 10 or 9 or 8 or 6 or 5 etc considering things like satellite geometry etc. That is not so as really if receivers were configurable (or configured correctly) then one would mask out the low horizon satellites, which are the ones that can tend to decrease the accuracy. Some manufacturers actually do this as a fixed setting but others don't and will accept all satellites (regardless) right down to the horizon. There is a point to useable channels but really to the sales/marketing people more sounds better. Accuracy has little to do with the number of satellites (hence channels) and all to do with geometry. Really the full 12 channels are used only a small % of the time but right now we have an overpopulated system (28) so we are a little spoilt. WAAS is different but the 1 or 2 channels that WAAS uses is really irrelevent to the result. Similar with DGPS as there are only corrections transmitted for 9 satellites and the same satellites must be in view at both locations for corrections to be applied. But to cut a long story short the "original" design was for a 11+1 but somebody got things wrong so everybody followed. Now would you have brought a 11+1 channel receiver if the opposition made a 12 Averaging certainly does very little for me these days. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, no that 100% true (that manufacturers "invented" the CEP accuracy and it certainly does "sound" a lot better). Really some units do provide 1m accuracy about 3% of the time but of course there's the other 97% that really counts. But really once manufacturers start stating accuracy figures around 3m and below then unless they also provide precision in the output to match (like at least 4 decimal minutes) there just blowing hot air. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, no that 100% true (that manufacturers "invented" the CEP accuracy and it certainly does "sound" a lot better). Really some units do provide 1m accuracy about 3% of the time but of course there's the other 97% that really counts. But really once manufacturers start stating accuracy figures around 3m and below then unless they also provide precision in the output to match (like at least 4 decimal minutes) there just blowing hot air. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Is the format this or is the format that if it's not this one then it might be that one but why does one have to guess/assume. What happened to minute' marks or second" marks, why should one have to guess? Formats can be written so they are very very clear and unambiguous. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Is the format this or is the format that if it's not this one then it might be that one but why does one have to guess/assume. What happened to minute' marks or second" marks, why should one have to guess? Formats can be written so they are very very clear and unambiguous. Cheers, Kerry. I never get lost everybody keeps telling me where to go

If it feels good then do it but if you achieve a result less than 13m 95% of the time (actually a little more since that's based on SIS) then you've achieved the system's specifications. Actually maximizing the constellation by being on site at the best time of day would give a greater sense of "knowing" that you've taken full advantage of what the system could provide on that day, which would be more important than averaging as averaging bad coordinates only produces a bad average. Cheers, Kerry. I never get lost everybody keeps telling me where to go

If it feels good then do it but if you achieve a result less than 13m 95% of the time (actually a little more since that's based on SIS) then you've achieved the system's specifications. Actually maximizing the constellation by being on site at the best time of day would give a greater sense of "knowing" that you've taken full advantage of what the system could provide on that day, which would be more important than averaging as averaging bad coordinates only produces a bad average. Cheers, Kerry. I never get lost everybody keeps telling me where to go