Kerry.

For a start there is no such thing as the “1927 National Vertical Datum Final Adjustment 1974”. NAD27 is a horizontal reference datum and NVGD29 (National Vertical Geodetic Datum 1929) was usually used as the vertical reference on NAD27 mapping. NAVD 88 replaced NVGD 27 as a vertical datum and is a better representation of the vertical but neither of these is exactly correlated with the Geoid and height issues where deflection of the vertical is incorporated. 1974 was the year the NAD83 horizontal adjustment was commenced (officially July 1, 1974) and how 1974 relates to a 1926 vertical datum that never existed is beyond me. As for “mixing” Selective Availability up with all of this (apart from basically everything being totally mixed up anyway), what’s SA got to do with anything, especially with the deflection of the vertical? Terminating SA allowed public access to data and whatever? what rot. Cheers, Kerry. I never get lost everybody keeps telling me where to go

4 digts , unfortuneately there's many that can do that (in a round-about way), but probably wouldn't matter if there were 5, 6 or more digits Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Railfan:This is part of my problem. I've tried several different applications for the Palm and none of them report the GPSr's accuracy (within xx feet). For one a GPS really has little idea how accurate it is anyway because it simply doesn't know exactly where it is in the first place. The accuracy that manufacturers estimate is just that an estimate anyway and varies depending on how the manufacturer implements the calcs. Not all manufacturers make this estimated accuracy available to secondary devices even if the software supports this type of function/output. Comparing to a "known" point will give one an indication at that specific point in time but that difference doesn't necessarily equate to what accuracy is. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Land survey requirements are basically different to pure positional requirments with respect to GPS as such as there's a whole heap of "other" things to take into account apart from the pure position in the real world. You are getting these 2 very confused. Points on the ground are physical points and they're there to denote real property boundaries relative to the cadastral system adopted by that country. I'm not saying the real property system is outdated but certainly some of the geodetic datums have been superceded and in time will certainly become outdated. With changes in datum, ellipsoids etc the coordinates of the "same" point on the ground can be (are) different. Similar with identical points in different datum's they are different physical points on the actual ground. Surveyors now they cover a whole range of expertise and Maps, well maps in 2 different datums are 2 different maps and in countries where datum changes are now taking place that fact can be certainly confusing if one isn't aware of the effects of datum change. As for Benchmarks GPS has no "direct" or "absolute" relationship to Orthometric heights as most countries still base heights relative to sea level. Still much to understand about the geoid and graviational effects before direct derived orthometric heights form GPS is possible especially within the higher class and order levels. I'm not here to be a consultant, more of an interest and I didn't know I had to hide/find things to discuss any of this (being doing that for more years than I want to remember), especially some of the myth and magic stuff. Lets just say I specialize in all things Geospatial. Cheers, Kerry. I never get lost everybody keeps telling me where to go

This discussion hasn't even come close to being on track and until you actually say what you mean and mean what you say so others can understand the vagueness of what your trying to say then like I said time will stand still. And that's about all Echo-1 and Echo-2 could do was reflect radio waves as they were nothing more than a mylar ballon coated with aluminium. Echo-2 the bigger of the 2 at 41 metres was even less successful than Echo-1, which didn't do much either. But what those had/have to do with land surveys and initial points has me a little puzzled Initial points, geez nothing new in them, all local datums had an intial point but times have changed (I'll say that again times have changed) and things have changed. You know even Australia has/had one of these thingies. http://www.auslig.gov.au/geodesy/datums/agd.htm The Johnston Geodetic Station is the initial point/origin for all old (note that is "OLD") geodetic work in Australia but it's now basically a historical monument. Significant based on it's history and importance more so in days gone by. Note the following comment "The adoption of this origin and best fitting local ellipsoid means that the centre of the ANS does not coincide with the centre of mass of the earth but lies about 200 metres from it" You see back then based on the best information available this was how things were done and similar things were done all over the world even in the U.S, which has it's local NAD27 origin out in the middle of some corn field. Where it is doesn't matter as much as the fact that there was one and that's the best that could BE DONE AT THE TIME especially considering the varying amount of old (and newer) survey data that was combined to produce something like NAD27. Now if you've got something that really makes sense instead of trying to make all this black magic hooah out of nothing then please feel free. BUT at least spell out what your trying to say. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Manually inputting elevation or even the ability to manually enter elevation with most comsumer grade receivers will only exist with a 2D fix. A 2D fix is something that is not commonly encountered these days. Generally it was only a viable option in some marine applications but today it's not something that's really worth considering. Elevation in general will always be less accurate (relative) than horizontal (for all users) and in cases where multipath is a problem then there certainly will be spikes (big spikes). Simply accept 3D mode and accept the elevation for what it's worth and sometimes that's not worth a lot. Cheers, Kerry. I never get lost everybody keeps telling me where to go

It probably has to do with being able to inter connect fishfinders/sounders using NMEA to GPS units. The sounder is then able to display positional information (from the GPS) to the user along with the bottom information all on the one screen. As well as that the sounder supports the export of depth information and GPS units that support the input of depth information are able to save/record that depth information as part of the waypoint. Cheers, Kerry. I never get lost everybody keeps telling me where to go

you as an individual could no more teletype a message to Echo-1 or 2 as jump over the moon. Both Echo 1 & 2 were simple passive satellites which simply functioned to reflect radio waves similar to how light is reflected by a mirror. As for timing and finding them the dadgum things were visible to the naked eye. Be interested in knowing the last time you saw these as both re-entered and distintegrated in the 1960's Cheers, Kerry. I never get lost everybody keeps telling me where to go

you as an individual could no more teletype a message to Echo-1 or 2 as jump over the moon. Both Echo 1 & 2 were simple passive satellites which simply functioned to reflect radio waves similar to how light is reflected by a mirror. As for timing and finding them the dadgum things were visible to the naked eye. Be interested in knowing the last time you saw these as both re-entered and distintegrated in the 1960's Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Team GPSaxophone:.... I see no reason why the 'civilian' GPS signal won't someday be upgraded to be more accurate. With the European version of our GPS (Galileo) coming online soon, it may spur our government to compete and hence, upgrade our signal. No real need to "compete" but "modernisation", well that's already underway, right now. quote:A dual (GPS and Galileo) receiver would be capable of averaging the two to give more accurate coordinates anyway. Averaging and dual GPS/Galileo, even less reasons to have to worry about averaging . But there's sort of been this option with GLONASS and at least GLONASS is partially still up there where as Galileo still has to get of the ground. Many manufacturers also made GPS/Glonass receievers but not many were confident in releasing them. As it turned out that became a justifiable lack of confidence. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Ever see a surveyor using a "chain" (a real chain) these days? Why not, well that one might really shock and surprise you. As for crazy, who knows? but one thing for sure this is the 21 century and the rest you appear a little (quite a lot actually) confused with. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Raoul Duke:.... The government DOES still use SA selectively in certain areas, but we get a notice when they do that giving the times and affected area .... If that being the case then that would have to be unclassified information. Where does these notices originate from especially with regards the "specific use" of Selective Availability. By specific use of "Selective Availability" I mean actual SA as opposed to other types of warnings like http://www.aopa.org/whatsnew/newsitems/gpstesting.html, which is not SA. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by nincehelser:I've noticed less accuracy in the last week. I've no idea if this could be the cause, but I read something interesting in a book called "GPS Made Easy" by Lawrence Letham. He says that during the Gulf War, the GPS constellation was changed to provide more coverage in the Middle East. This left less coverage in areas such as California, and people there noiced their receivers were not working as well as they used to. During the Gulf war GPS was still in the "construction phase" and consisted of only 16 satellites (3 Block 1A, 3 Block 1R & 10 Block IIA's). These still only gave a 2D fix (minimum 3 sats) for 19-20 hours each day and 15 hours of 3D fixes. These weren't changed about per say as much as the new craft that were launched during the conflict were put in orbits that best suited the middle east. The satellite that was launched on the day of the invasion (Aug 2) was activated in a record 22 days. NavStar was only declared operational in 1995 so back in 1990 things were far from perfect considering war is a 24 hour job. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One thing I will add if SA ever goes live again (which it won't) it would take a matter of seconds to be detected, and the fact broadcast that's for sure. That is if the WWW was still alive and running. However if SA was ever required again (over and above Selective Deniability) then one would guess that with things that bad there simply wouldn't be a civil signal what so ever. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Don't worry, know exactly who owns them, what they do and what they can't do and the response is still the same. "Encryption" to some extent in GPS terms has more to do with AS (Anti-Spoofing) than SA but there is a connection. Actually if someone using a GPS can't tell if SA is on or off then they really want to give it away. 100' ain't really a problem as that is even less than the actual spec of 36 metres @ 95 % (worst case scenario). Cheers, Kerry. I never get lost everybody keeps telling me where to go

No, there's been no evidence of SA ever having been re-activated. Satellite 22 is out of hospital, alive and well with a still overpopulated constellation compared to the specs. I'd hate to hear the complaints if ever the system ever gets towards the lower minimum end of the specs Accuracy even in Brahrain is currently running around 3 metres @ 95% and Kibutz (Israel) a little over 3 metres. For the 48 hour period 23/11 to 25/11 the local accuracy here (my place) was 2.15m CEP or 2.95m RMS or 4.4m @ 95% depending on which value sounds the best even though they are mean the same thing. Cheers, Kerry. I never get lost everybody keeps telling me where to go

All this talk about accuracy, noticed the following changes mentioned in a software upgrade of one particular unit. quote:Improved the accuracy of the estimated accuracy That's like saying the estimated accuracy we displayed last week wasn't accurate so lets just "change" the accuracy this week and we'll review it again next week Cheers, Kerry. I never get lost everybody keeps telling me where to go

since this discussion started Oz has moved about 2.5mm north east (give or take poofteenth) and if things keep going the way they have been around here (nowhere ) then someone is going to have to convince the tectonic plate manager to suspend all movement until this matter is sorted out. Gee maybe mentioning this around here might not be the best thing to do this could be grounds for a real conspiracy Geez by the time there's any answers from #1 and things keep moving like they have (for the past zillion years) the mailman might no even find the mailbox . I wonder if it was similar back in the 1700's when Harrison changed the whole perpective of latitude. But I suppose thinking the world was flat came and went as well. Cheers, Kerry. I never get lost everybody keeps telling me where to go

#1, Precise coordinates to what your not being very forth coming in all of this. Starting to sound like you know less and less about more and more with everyday. You know precise coordinates is something some of use deal with/in everyday but until you starting unlocking these deep dim dark secret fascination with very vague and unclear one liners, then that's about all we're going to get out of this. Cheers, Kerry. I never get lost everybody keeps telling me where to go

A 38 Older Cheers, Kerry. I never get lost everybody keeps telling me where to go

you do have a point don't you? with all these half finished comments. It's really starting to sound like your making a lot of noise about very little. So spit it out and say what your trying to say instead of all this beating around the bush. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by kyleebrock:.... Here is a PDF message about 2 satellites being out dated 6NOV02. http://www.fs.fed.us/database/gps/news/06nov2002.pdf As mentioned in the doc 22 was out for a period but notice it is now back. Still 27 in the constellation. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Stats, what Stats. Hidden: 0 Found: 0 so what . Stats will mean whatever people want stats to mean but people shouldn't be fooled by stats alone. Cheers, Kerry. I never get lost everybody keeps telling me where to go

well I've got to say I'm not all that sure of what your trying to say, and what's even worse I'm not all that sure that you know what your trying to say . So cut all the gobbly gook and words which used in the context make no sense what so ever and try and explain all this meandering waffle in something that does. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Is 1998 old Cheers, Kerry. I never get lost everybody keeps telling me where to go