Kerry.

Lets hope they all come to pass on and get replaced by the nextest and bestest version, don't you get sick of the same old satellite day after day after day. But actually there are some satellites being shutdown that are used for tracking but these are not GPS sats so maybe your getting things mixed up a little. Cheers, Kerry. I never get lost everybody keeps telling me where to go

16 miles is certainly not Datum (or really format) related. Really to be consistently off by 16 miles sort of tends to indicate the coordinates have an issue or you simply weren't where you thought you were or supposed to be. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Find this a little strange that after a number of caches it appears to be so many feet always in the one direction of the actual cache coordinates. So if ALL the caches were placed by the ONE person then who is to say who is right or wrong. However one would presume that different people placed these caches and hence there's really no way known that they would all perfectly agree with other and appear to make one appear to be always so far off in the one direction. Eraseek, what you are thinking of is PCF (Position Correction factor), which is what some (old) units used to correct for different datums basically because these units never had any datum option anyway, just WGS84 (fixed). Don't see it used all that much these days. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Lat/Long and UTM coordinates must be referenced to a datum. UTM is basically a projection of the Lat/long vales, which in turn are a function of cartesian (XYZ) values. The same coordinates used with different datums will be different physical points or the same physical point will have different coordinates relative to the respective datum. Also with UTM one also requires the zone otherwise the coords are basically useless. Cheers, Kerry. I never get lost everybody keeps telling me where to go

PRN11 is alive but could have been unusable when that specific almanac was created, which might have been the case as PRN11 (SVN46) was unusable for a short period about a week ago. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Some of this PLGR accuracy stuff really needs to be put into context as PPS receivers have other capabilities to improve accuracy apart from C/A, P and encrypted P(Y) codes. Any receiever (each and every individual one) with a PPS module (in use or not) is classified and must have written approval from JPO, USAF. Prior to SDGPS PLGR's used Wide Area GPS Enhancement (WAGE), which is spec'd at <4mCEP as the first PLGR's couldn't use differential because PPS is not based on pseudo-ranges, so SDGPS wasn't an option. The newer PLGR's with SDGPS capability, the accuracy is less than 1m but none of this type of accuracy is possible without augmentation of some sort. If PLGR's were as accurate as some claim then there'd be no reason in spending the $$'s developing some of the other military real-time systems, which are accuracy critical. Cheers, Kerry. I never get lost everybody keeps telling me where to go

"Draws on a completely new technique, known as Satellite Differential GPS (SDGPS)" . Well SkyFix has existed since 1990 and has been a Satellite based correction system since then. This is simply an extension of that initial system, which had an accuracy of sub 2 metres within 2000+ km from a reference station of which there are about 50 worldwide. As with any GPS, accuracy will cost and SkyFix will cost more than SkyFix/Premium. All require a decoder, a yearly subscription and to get 10cm from XP requires a dual freq receiver. Not even close to a conventional handheld at this point. Satellite differential isn't something new as there several other companies (like OMNISTAR )that provide a subscription service as well. WAAS is even a SDGPS system. Accuracy costs Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by jimmynholly7677:it looks like my datum is on the IRAN datum will that effect accuracy??> Ignorance is no excuse!!!! If your not in Iran it certainly will, big time. Even if you were in Iran and not using Iran based coordinates then it still would be affected. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Everybody keeps quoting accuracy but what type of accuracy as say 3 metres certainly isn't 100% of the time. Is that 95% or RMS or the manufacturer preferred CEP, which of course sounds better but it ain't. If 3 receivers quoted accuarcy figures of say 3m CEP, 5m RMS, 8m@95%, which one is the better, None in accuracy terms all a equal. It's not simply the number of metres/feet etc but what type of metres/feet they are that counts. Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on May 07, 2003 at 08:24 PM.]

Know of several instances where even trained emergency services people (fire, ambulance etc) have sent Helo's in the wrong direction but rescue pilots generally pick these types of things up fairly quickly especially if when the course/position is exactly like the emergency yesterday. Why, arrive at an emergency, do all the right things, turn on the GPS, give the position WITHOUT waiting for it to acquire properly. Many pilots now ask to confirm positions based on physical ground locations, just to be sure. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Now that SA is off that's a bit of a myth as there isn't all that much difference now in accuracy. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by TotemLake:The only reason I can see why it would be worse instead of better is if you would find yourself in a very narrow window of satellites instead of the optimal wide geometry of same. My observations on the averaging is it takes the normal swings of the estimated position and begins to settle it down to a much more narrow position. Yes, there will still be swings, largely due to the signal being handed off from one satellite to the next as it goes over the horizon and I have seen swings as large as 350 miles but I don't think this is just a Magellan problem. Granted, I haven't the means to compare the Magellan against the Garmin to say which is better, but I can say I am confident that the laws of averaging are going to get me closer to the target more times than without it. TL, Averaging say a narrow window of satellites (like in a creek, canyon etc) will still only be an average of the available data. If the geometry is weak, the position solution will generally be weak and so will any average of that position solution. Averaging bad data basically only produces a bad data average. It's hard to manage those type of swings, which in reality aren't all that common but that's where the other 5% of the accuracy spec fits in. These days the position solution track is slower moving and if it's wandering around say X number of metres from the real world coordinates then it takes a little while to make much of a difference as far as averaging is concerned. It's not as if the position solution is X metres north then suddenly X metres south then X metres West then X metres East as that simply doesn't happen, which is why averaging is an unknown quanity. One might start averaging when X metres north and if after several minutes of averaging the position solution has been slowing wandering further north then the average is worse than the first initial reading. Of course if the reverse applied then the final position might be better but one doesn't know this at the time. quote:....I am confident that the laws of averaging are going to get me closer to the target more times than without it In GPS terms those laws of averaging are 50/50. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by nincehelser:Speaking of WAAS... .... but could it actually degrade your position accuracy under poor condtions? One could call this situation "poor conditions" as in this case using WAAS outside the ground stations (like Australia) will certainly degrade the position. Just because one has a "WAAS signal" doesn't mean one is receiving valid (or any) "WAAS corrections" Cheers, Kerry. I never get lost everybody keeps telling me where to go

Nothing that can be calibrated really. Powerlines can cause interference in themselves depending on the voltage and other issues. Steel towers can be an "obstruction" in themselves and in conjunction with "interference" can combine to hassle any GPSr. The cache your looking for isn't perfect either and all things being considered then it might all be normal. Might simply be circumstances (at this time). Cheers, Kerry. I never get lost everybody keeps telling me where to go

NO not a real good idea and there's really not a serious connection between SAR and Geocaching. As for being a volunteer fire fighter then that's different, might not be paid but certainly trained as one. That's not to say a geocaching couldn't/wouldn't become a SAR member but don't go into it thinking that training (and in some cases re-training) isn't required. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by TotemLake:.... where the Magellan users will keep their GPS out most of the time because it will direct them closer with the autoaveraging. No there's no real truth in that statement these days due to many reasons and many different variables at different times. In affect (despite what the manual might says) autoaveraging can actually make the position worse. Autoaveraging is one of those things that if it feels better using it (but then one really doesn't have a choice with some units) then do it but it's really only a feel good thing as there's nothing to indicate at the time if the results are better or worse. Cheers, Kerry. I never get lost everybody keeps telling me where to go

If you live in Australia you will have extremely poor WAAS capability, so much so that's it's totally useless. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Might explain the "metres" (6 figure eastings, 7 figure northings etc) bit HERE under "What is a coordinate system" as far as the maps you are probably using. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Brian - Team A.I.:With that article being over 2 years old now, and some of the advancements in GPS technology, would that still hold true? Hold true, Yes as the underlying principles haven't changed and neither has GPS technology as in the "actual" GPS side of things. Even with SA off the relative difference still exists. Actually there's really been no new advancements in GPS technology (proper) for quite some time. However things will catch up in a rush over the next few (or more) years. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GPS guided shopping trollies IN super markets, aren't we sort of missing something here Cheers, Kerry. I never get lost everybody keeps telling me where to go

More than likely the map and something to check at other different locations maybe. Calibration, NO, no an option in the thinking that position error can be calibrated. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Consistent, wouldn't even come close. The error can be at least twice (and up towards 3 times) the horizontal error. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Unfortuneately the good old level and staff isn't going to be entirely replaced anytime soon. Geoid separation and gravity in an absolute sense for GPS heighting principles simply isn't adequate for many purposes. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GDA for all intent and purposes is identical to WGS84. The Etrex converts things ok. GDA94 is a datum so positions can be Lat/Long as well as UTM. UTM coordinates in GDA94 are commonly referred to as MGA (being Map Grid of Australia). The Etrex will accept either Lat/Long or UTM in WGS84 (GDA94) and allow the user to configure the position format display as either Lat/Long or UTM. Will also allow the input of AGD66/AGD84 (Lat/Long or UTM(AMG)) and allow conversion to GDA94 (WGS84) and vicversa. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One issue with Australian charts/Maps at the moment is the mixture of datums as things are changed/updated from the old(er) AGD66 or AGD84 datums to GDA94 (WGS84). Important to make sure of the datum of the coordinates before converting to/from lat/long. As long as you know the full AMG coordinates (and Zone) in either AGD66/84 (Australian Geodetic Datum 1966 or 1984) or MGA94 (Map Grid of Australia 1994) then converting either way won't be a problem using most (not all) GPS receievers or conversion software like GDay or GDAit etc. This conversion software is freely available was well as national distortion models but if the GPS receiever does it then probably better to do it that way. Cheers, Kerry. I never get lost everybody keeps telling me where to go