Kerry.

Testing handhelds, the further away the hands (people) are the better. Even the people holding those handhelds contribute to possible errors. Many things matter as the constellation is dynamic and constantly changing along with atmospherics and all sorts of other things. Variations will certainly be caused during the day and not necessarily night being better than day depending on ones physical location. Different parts of the globe have different influences and conditions. In any 24 hour period of 1 second recorded data about 95% of all errors should be trapped, 30 days to trap 99.99% of all general errors. Cheers, Kerry. I never get lost everybody keeps telling me where to go

UTM within 3 feet, not so. What is it so that one converts 3 decimal minutes to UTM and all of a sudden UTM is within 3 feet. 3 decimal minutes isn't even within 3 feet. Cheers, Kerry. I never get lost everybody keeps telling me where to go

0 feet well at least this wasn't a serious question, perfect day or not. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Low horizon Satellites defeat the whole ideal scenario as these also have the most noise due to more atmospheric interference. Even though most recreational receivers have fixed cut-off masks generally around the 0-2 degree mark those extra low satellites generally degrade accuracy. For this reason serious GPS receivers have user defined masks and settings of 15-20 degrees eliminate these low problem satellites. Cheers, Kerry. I never get lost everybody keeps telling me where to go

As you've mentioned elsewhere the best mathematical model (as far as simple geometry is concerned) is a tetrahedron but in practice that's simply not achievable. There's so many variables in this one really wouldn't know where to start. One reason why most GPS spec is statistical with average and worst case scenario's based on specific combinations, which basically give different results. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by georapper: .... i will include the timing errors, propagation errors .... make believe propagation errors yeah right. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by georapper:.... how does the receiver get an updated time equivalent to the atomic clocks on the gps satellites? it shouldn't take 4 satellites because i can get a 2D fix with 3 satellites so a 4th should not be required to update the receivers cheap clock to atomic clock accuracy. any ideas? More than ideas as the "timing" mechanism involved with GPS is what makes it work as it all has to do with "timing" but not necessarily "time". Effectively 4 satellites are required for a 3D fix and as you mentioned a 2D fix requires 3 satellites. The 3 satellites required for a 2D fix is the minimum to solve for the 3 unknowns, XY & Time/ing. However height is still required and for a 2D fix this can be either provided by the user or assumed from the last fix. A 2D fix really isn't accurate if a reciever is constantly and continuously changing elevation. 4 satellites required to solve XYZ & Time and if any of the unknowns (except time in a practical sense) can/could be supplied then for each known value then 1 less satellite is required. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GPS errors are certainly not "unbiased" and certainly not random in the pure statistic sense. And it's simply not a misconception that if one is averaging data that is trending away from the truth (which GPS can do for reasonable periods of time) then the average will in affect be tending to make the position worse. The problem with GPS is errors (for want of a better term) especially in the days of Selective Availability were certainly not random but certainly not predictable. Generally of any 24 hour period 95% of any errors will be trapped, which will certainly give a reasonable average if averaged over that time frame, however that's certainly not practical. A 30 day cycle is required to trap most errors. These days without SA averaging doesn't contribute any reliable outcome to the solution apart from knowing there's a 50/50 chance of getting a better result but of course there's a 50/50 change of getting a worse result and only hindsight will verify this. Even though GPS accuracy is based on statistics the real world affects of averaging both pre/post SA are quite different Practical example of GPS averaging More practical aspects of GPS averaging Some aspects of GPS averaging with respect obstructions Cheers, Kerry. I never get lost everybody keeps telling me where to go

Magellan Old product manuals Cheers, Kerry. I never get lost everybody keeps telling me where to go

Fizzy, one other thing I forgot, which is one of those which side of the fence issues with UTM and zones. As you would no doubt be aware zones are 6 degrees wide with half a degree overlap. I see that a longitude of say 156 00' 00" (as an example) can/could be either zone 56 or 57. Of course if someone was working with coordinates all in zone 56 (and that could include longitudes out to 156 30') then they might want the UTM coords to be in a specific zone especially for a zone overlap situation. It appears that 156 00' 00" by defualt goes to the next highest zone (in this case 57). Is that your plan or do you have other thoughts on handling zone overlap issues? Distance, Azimuth and Reverse Azimuth look ok. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Fizzy, some comments. As for using it outside the continental US or more importantly out of the northern hemisphere it appears to give negative northings (easting is ok) for the southern hemisphere, which would indicate issues with false origins. Correct coordinates (within proper ranges of minutes and seconds) are ok but it does some quirky things with minutes & seconds out of valid range. My opinion with systems like this is they should prevent users from inputting out of range (incorrect) formats where users confuse one format to be another. A quick example is say a latitude like 23 00.61' (assumed north), input as 23 00' 61" gives N 23 01.017' ( N 23 01' 01.00"), which is correct to a point but really shouldn't be allowed. Where as if input as a southern latitude -23 00' 61", gives S 22 58.983', which indicates it's not applying the appropriate signs correctly as -23 00' 61" could (should but not entirely correct to do so) effectively be called -23 01' 01" That's all I've had time to look at. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Also at the time of the first Gulf war Garmin was only relatively new to the market, while some other companies had been developing products for around 5-6 years before the first Gulf war. Magellan had produced the first commercial handheld GPS in 1989, which was about or even before Garmin starting into GPS. Trimble had some of the first products on the market in 1984/85, which was also about the same time that Sercel (predecessor of Magellan) produced its first receiver. Cheers, Kerry.

There's many other manufacturers besides just Garmin but some had existing contracts and presumeably if the request was for non military type receivers then those with existing contracts would have had first option. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, have a little look at this lot then (in your spare "time") Time Lords Becoming very serious stuff, seriously. Cheers, Kerry. I never get lost everybody keeps telling me where to go

No, there's something more to this one than simply elevation changes but the concept of changes in elevation will always make the GPS trip shorter (all things being equal) than the path the feet followed but certainly not by that much. GPS measurements (trip distace) do not take into account changes in elevation. If you looked at it this way if the GPS trip was 5.14 miles and the actual distance more like 7.14 miles then that would be akin to walking up a continuous slope of about 45 deg (which is quite steep) and at the end be almost 5 miles high. Cheers, Kerry. I never get lost everybody keeps telling me where to go

And it's basically the advanced Rubidium's on the Block IIR's (and IIR-M's) that have given improved performance in timing and position. We just need more of them but many of the existing Block II's/IIA's simply won't die quick enough. The Rb's on the II/IIA's are basically 15 year old technology and the more IIR's with the new Rb time standards we get the better. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, interested in the time side of things, then the following is a cell phone tower site. That cone shaped looking thing is a fixed GPS antenna connected inside to basically a GPS receiver. Doesn't go anywhere, doesn't move, just tells the time and keeps the network in sync. everybody keeps telling me where to go

Getting a little mixed up here, I think. Really what the user prefers is not equiv to what a person might require. Sure if a person wants a compact internal antenna model then that's what THEY want but if that configuration doesn't do the job then that's their problem. They either accept that or look for ways/methods to improve things. As for many of the other comments Bob it's probably safe to say a similar approach applies. Like the "which is the best GPS" query, no specific answer without specific details. Much like "dense tree cover", what is dense tree cover to you might not be dense tree cover to me. As for time, nobody is making an issue out of time apart from the fact that some receivers do a lot better at doing things than others but then it depends on many other things. What is relevent to some is not necessarily relevent to others but myths need to be corrected before they become fact as they have in the past. What some see as just a GPS unit that gives position is not the only function of the system remebering that NAVSTAR does stand for NAVigation Satellite Timing And Ranging and many forget the important Timing and Ranging functions that GPS actually provides other users. As for WAAS having enough processing power I doubt if WAAS could ever have enough processing power. Sure it might be enough but if WAAS was as stable as some claim then there wouldn't be so many questions about why it doesn't work for them. Really WAAS has been blown out of proportion and WAAS actually took a hit when SA was discontinued. Is the improvment in accuracy worth the 6 thousand million dollars it has cost, so far. Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on September 04, 2003 at 06:44 PM.]

quote:Originally posted by GunPowderBoy:Sorry, It is .28 mile. Still is the same theory though.These guys know what they are doing, just never seen anything like this before. With what information you've provided above I wouldn't say they now what they are doing. What's the whole story? as the information you provided means nothing. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by junglehair:I wish you wouldn't tell people not to bother averaging their waypoints .... The same logic for averaging during the days of SA still apply today. If you take the average of multiple readings, you reduce the error. It only takes a few extra minutes and IMHO it's worth the effort. Worth the effort, not so, reduce the error? how do you know (without recording data and comparing it to the real position). I'll defy anybody to machine average coordinates for a few minutes then GUARANTEE that average is better then the position started with. Averaging in no way today can be compared to averaging when SA was active. Cheers, Kerry. I never get lost everybody keeps telling me where to go

EraSeek, for sure the displayed receiver time is corrected via satellite broadcast messages but as Anders mentioned once the receiver gets bogged down doing some real work, stuff like the time display update is probably dropped from the list of immediate important things to do and gets a little behind, always behind never in front. Still by far the best timing device there is, leap seconds and all. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Silent Bob (& Fuzzy), with relation to antenna's the issue with handhelds (and built-in antenna) is they can be pointed any which way and actually if handhelds weren't detuned as far as signal recpetion was concerned many wouldn't maintain a WAAS lock for more than a few seconds. An external antenna in most cases would make one hell of a difference to reliable WAAS reception, assuming suitable reception and of course not everybody does get suitable signal reception. Really the recreational side of WAAS software doesn't take into account the full capabilities of WAAS and it wasn't all that long ago that receivers marketed as supposedly 1 second position updates, simply couldn't achieve that claim either. Even quickly looking at output these days it appears 1 second update but it's more like a 1 second output, with the same computed position output for several/many seconds in a row. That simply points to lack of processor power (or basically priority being directed to the primary purpose of a GPS receiver, position, position, position) in many cases but things are getting bigger and better but at a cost and cost is what most manufacturers have to keep down. Sure manufacturers could pack a wack of power into a handheld but not many would be sold compared to other models. Bit of a compromise, processor power, battery power/life and cost. Similar with displayed time, a recreational GPS receiver doesn't give much priority (really at all) to worrying what the time is, if it's a few seconds out nobody really cares. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The theorical elevation (barring all obstructions) through out Minnesota, ranges from 20 (SE corner) to 29 degrees (NW limits). However attempting to use WAAS in the type of application that many try to use it, has to accept the fact that WAAS was never designed for land based activities. It appears to have become more a marketing tool than anything that is guaranteed. One simply shouldn't have to reset, reboot or re-install software and wait ages for a system like this to work. My perception is WAAS installed on a handheld is out of its depth, out of its intended evnironment and application and a low end handheld simply doesn't have the processor power (or antenna design) for it to be more than a gizmo. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Anders.:Hmm, that kind off implies that I wasn't kind, when I responded in public. I hope you weren't offended that much... .... If nothing else, Kerry starts nagging when something technical is off road. Nagging , now that's a qaint way of putting it. But yes I did notice things were a little lost but you had already remedied the situation fairly well I'd thought, so didn't have to nag Cheers, Kerry. I never get lost everybody keeps telling me where to go

As far as the actual GPS side of things is concerned the dream GPS really has not a thing to do with GPS (proper), but some third party developer that incorporates a GPS engine into something else. GPS is GPS and as such as the system is concerned there it will stay. I suppose it like things like marine chart plotters being called a GPS (which in reality is not entirely the case), but in effect it's just an application that uses feed from a GPS engine and that data feed doesn't have to necessarily be part of the chart plotter. Really the next generation of GPS has not a lot to do with anything other than the system proper. It all gets back to the age old question of exactly what a GPS is? Cheers, Kerry. I never get lost everybody keeps telling me where to go