Kerry.

quote:Originally posted by dave and jaime:kerry, sats 21 and 22 are dead? does the government have any replacement plans in mind and are the replacements compatible with present equipement? There hasn't been a replacement launched since Jan 2001, as the constellation has been very healthy with a reserve capacity. Actually still can loose a few more before things really get critical. Those extra's certainly are handy but. The launch of GPS IIR-8 was deferred in late October 2002 due to damage to the launch vehicle and hasn't been rescheduled. GPS IIR-9 is for Feb 6 2003, IIR-10 April 6 2003 and IIR-11 August 11 2003. All replacements and future replacements (about 12 of the IIR's modified as IIR-M) will be compatible with existing equipment on L1. Everything should be backward compatible even when the IIR-M's and the IIF's make available civil L2 and latter L5. However to use L2 & L5 I would imagine by then (~2006/8+) there would be some new receivers in the market. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Even though sats 21 & 22 have died, looking at some recorded data over the past 6 days between Miami & Savannah Beach Georgia there appears not a great amount of difference and still appears the accuracy is within spec (based on this period). Cheers, Kerry. I never get lost everybody keeps telling me where to go

One thing with surveyors (as Kewaneh alluded to) is not the fact of simply pushing buttons but "knowing" why one is pushing buttons AND then knowing what to do with the data from that button pushing. Really there's quite a range of different types of GPS surveys based on accuracy and requirements specific to the type of survey and the requirements. Real-time cm type accuracy has it's purpose but is basically restricted by distance as a function of radio transmission and ambiquity resolution. With static it comes down to time and basically the longer the line the longer the time required. Where as with real-time stuff (RTK etc) receivers are running generally at 1 second epochs where as static might be recording every 30 second epoch but maybe for hours, days, weeks etc but distances in the thousands of km is possible to less then cm accuracy. Machine control systems can be set to transmit 10 updates a second and some can actually do that (at a cost $$) where as lower cost units can manage 10 outputs a second but only based on a 1 second position update. The systems are there to meet the needs and the $$'s basically follow. Real-time systems such as the automatic Aircraft carrier systems run at 20 Hz (20 position updates per second). The requirements are to land a carrier jet (like a FA-18) on a carrier at sea under auto pilot. This basically requires the hook to "fit" through a 3 foot square window 14 feet above the end of the carrier deck so as to meet the arrestor wire. There are multi (as many as 6) movement dynamics based on the carrier doing X number of knots with the similar addition of the aircraft dynamics (roll, pitch, yaw, speed, drift etc etc) all on an angled run way at a closing speed that jets need to fly at. The dynamics is mind blowing and it's one cool pilot putting their faith in a GPS landing system at that level. But there is a system and it's been tested under sea conditions. That's off the track of conventional surveying but there's still a long way with GPS yet even better than cm or mm survey requirements. Cheers, Kerry. I never get lost everybody keeps telling me where to go

What's your approx location (within a few hundred NM will do). Cheers, Kerry. I never get lost everybody keeps telling me where to go

Was the PDOP part of the software patch as well or part of the base 3+ display. Be interested in obtaining that software patch if you could point in the right direction. By native format one would assume you are referring to ECEF XYZ, which is the underlying (and native) GPS coordinate system. Cheers, Kerry. I never get lost everybody keeps telling me where to go

2 things with native coordinates and PDOP. PDOP isn't displayed by too many receivers (at all) to know if it's greater then 2 or not. Besides PDOP can go a little higher than 2 without too many worries. The specifications are based on a PDOP of 6 or less. Native coordinates aren't displayed by any recreational receivers either. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Averaging, isn't all that it's cracked up to be and basically is comes down to a 50/50 chance of improving or actually making the position worse. The thing is one doesn't know at the time which 50% one is dealing with. http://www.cqnet.com.au/~user/aitken/gps/gps_avg.htm http://www.cqnet.com.au/~user/aitken/gps/gps_obs.htm http://www.cqnet.com.au/~user/aitken/gps/avg_pii.htm Averaging bad data simply gives a bad data average. Cheers, Kerry. I never get lost everybody keeps telling me where to go

#1, yes you certainly are lost Cheers, Kerry I never get lost everybody keeps telling me where to go

The option will always be there to use straight L1 (as it is now) if ones wishes to do that . That's going to be the users choice. In the meantime even before these IIF's fly with the new civil L5 (and L2), 12 of the existing built and currently stored IIR's are being modified with L2 which will mean civil dual freq many years ahead of waiting for enough of the IIF's to be usable (~ 18 sats in 2012). The modified IIR's (known as IIR-M) in conjunction with the first of the IIF's will give an 18 satellite constellation in about 2007-2008? But yes new hardware, unfortuneately not just software unless purposefully built in hindsight. Then of course there's the GPS III's currently being considered. But civil L2/L5 isn't going to give cm accuracy (compared to L1 mode of operation) but maybe one will have to get used to hiding things better (within about 1.5m ) Cheers, Kerry. I never get lost everybody keeps telling me where to go

GPS stands for Global Positioning System but it's much more than simply a positioning system hence the formal name NAVSTAR GPS (NAVigation Satellite Timing And Ranging Global Positioning System), the world's first global utility. Timing and Ranging functions are an inportant part of this system and in that regards one might differentiate between what some call a GPSr and straight timing and ranging equipment. Maybe it should be GPSu as that is what we are the "User Segment" as opposed to the Control and Space segments. Cheers, Kerry. I never get lost everybody keeps telling me where to go

NO, no neat website that does very specific and detailed analysis regarding all the variables but there is software that does this. The offer was if you had a specific date/time/location then one can look at what's going on exactly at that time and around that time. Sometimes this can highlight just what the problem/issue might be. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One reason why things like availability (and accuracy) is quoted as a statistic. Less than 95% of the time, then there's a less than 99% and also a less than 99.99% but there's never been and never will be a 100% guarantee as there will always be that 0.01% that nobody has a handle on. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The 38 originally appeared in about 1992 and the MultiTrac-8 trademark was a play on words as it tracked a maximum of 8 sats through a single channel. What let it down was the antenna but that basically changed with the 45 family and the "latest design" (then) in antenna's. As for accuracy well they gave little away (if anything) to anything. Cheers, Kerry. I never get lost everybody keeps telling me where to go

If your referring to dGPS similar to CoastGuard type stations then you'll also require an additional Differential Beacon Receiver, something like a Garmin GBR21 or 23. That would be the only differential signal a 12 basically supports. Cheers, Kerry. I never get lost everybody keeps telling me where to go

How much different? If it's in the few hundred+ feet then check the Datum's are the same. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by marty621:A 2 acre island, if it were square would be 295 feet square, a very small island. The best results would, and probably the quickest, would be to do a traditional topographic survey of the island. The results would be far more accurate than handheld GPS units presently in use could produce. Unless its heavily wooded or otherwise impenetrable, the field work would take no more than a half day. GPS doesn't make all jobs easy. That's probably about the best suggestion so far as quite frankly a handheld GPS simply wouldn't even come close to making any useful as far as contours are concerned. The handheld SPS Z would simply be totally too eratic and frankly useless. SPS Handheld, total waste of time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

NO, GPSr's aren't calibrated anywhere, no such thing. It's all a function of the system and what the reciever does with the information it does get. In Moe's case there is some "science" that could be used that "might" help decide who "might" be more right (or is that more wrong) than the other. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by MrGigabyte: .... 2) On the island, record waypoints at the significant "break points". These are all the high points, low points, ditches, ponds, outcrops, top of banks, bottom of banks, etc. You cannot have enough waypoints. These point are used to build a "TIN" model (Triangulated Irregular Network). The plane formed be 3 proximity waypoints should be perpendicular to the contours, if you took your waypoints in the right spots. Download your waypoints and track logs. Convert them into a delimited text file of X, Y, Z coordinates. For an SPS handheld that's a big ask and quite frankly a waste of time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by EraSeek:But Kerry, I think the ''Acuracy Circle'' IS suppose to be a visual version of the EPE. Why it would differ, I don't know. As it was written above I read the "measure distance function" as basically the distance from the GPS position to the target Maybe I read it wrong, I'll think about it some more. Whichway, could you also clarify things. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Estimated Position Error, it is nothing more than ESTIMATED and for many reasons does not mean that because the EPE is so many feet then that is the actual accuracy relative to the actual position. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Warm Fuzzies - Fuzzy:Gosh, I hope there's a resemblance between Clarke (let's pick 1866; that's a nice round number) and NAD 1927, since NAD 1927 is based on the Clarke 1866 ellipsoid. Resemblence yeah probably wrong word to use. Now the "Clarke 1866" ellipsoid and NAD27 datum do relate. Maybe I should have said Clarke (either 1866 or 1880) is an ellipsoid, where as NAD27 is a datum same as WGS84 but the WGS84 datum is based on the WGS84 ellipsoid and they're different things in geodetic terms. NAD27 is not an ellipsoid (as such). quote:The reason for this has nothing to do with NAD 1927 as a datum and everything to do with the imprecisions inherent in the conversion formulae. By splitting the continent into various regions, you can optimize the conversion factors for a smaller area and get less overall distortion. If everything you were doing were in NAD 1927 - for example, if you were surveying in the year 1945 - you wouldn't need to split up the continent. But I wouldn't call it "imprecisions inherent in the conversion formulae" as the problem with NAD27 stems back over several hundred years with the base data and equipment accuracies all rolled up into the one system. (maybe you meant the same thing?) In 1945 surveyors were still adding to the problem but didn't have the capability in those days to do anything about it. Similar sort of thing with AGD66 & AGD84 (Australian Geodetic Datum 66 & 84) both based on the same ellipsoid but different coordinate origins due to "additional information" and "strength" in the base data. Becomes a bit nasty and fragmented with overlapping regions. The quicker there's a uniform world wide compatible datum the better. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Waterboy With Wife (www):Kerry, you refer to the "underlying Cartesian coordinate system, which GPS is based on." I wish you would explain this more thoroughly. To me you are saying that GPS is based on a planar or flat earth model. Strange, I had always read and heard that since Clarke in the 1860s an ellipsoid model was used. Also that the Clarke, NAD 27, and WGS 84 were ellipsoid models very close to a sphere. Probably should have correctly referred/termed it as ECEF XYZ (Earth-centred, Earth fixed XYZ) or basically a cartesian system based on a 0,0,0 origin (centre of earth). GPS satellites being in geocentric orbits effectively rotate about this origin. All other "user" friendly GPS formats technically originate from ECEF XYZ. There's no real resemblance between Clarke (which one?) and WGS84 and NAD27 (and others) in geodetic terms 'cause if there was then there wouldn't be a need to have around 200 datums in most GPSr's to cover different parts of the world. Even with NAD27 some receivers have 11 "different" definitions (of the same datum!). quote:B. These jumps or inaccuracies in both length and direction may cause problems in precision surveying or navigation. Not to a surveyor it doesn't besides what's the problem. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, with regards mask angles some recent changes announced to the dGPS configuration, which undoubtedly will get adopted wordwide http://www.navcen.uscg.gov/news/MaskAngle.htm Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cachier:_OK, explain!_ Myth #1, the more satellites the better the accuracy. Also note "Precision" and "Accuracy" are 2 basically different (but related) things. Accuracy has all to do primarily with geometry (relationship of the satellites to themselves and to the user) as a whole heap of satellites with poor geometry simply will give a poor (inaccurate) result. Actually the more satellites used sometimes decreases the accuracy (even with reasonable geometry) especially low horizon sats which can introduce all sorts of errors in the position solution. But essentially it's the geometry that matters far more than number of sats. A position solution based on minimum sats with good geometry (better still minimum+1) has far more integrity and reliability than from an over populated solution with poor geometry. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The datum must match the coordinates and really has nothing to do with any particular area or location. To be usable ALL coordinates must be referenced to a datum and if one acquires coordinates without a datum then that's basically going to be a bit of a problem and a bit useless. And your right they could all be wrong. WGS84 & NAD83 for all intent and purposes used here are the same. NAD27 is an older localized datum. Cheers, Kerry. I never get lost everybody keeps telling me where to go