Kerry.

quote:Originally posted by Mr. Snazz:Actually it was Carter who lifted it, in 1998. Get with the program. Who's Carter and what did he do again? Cheers, Kerry. I never get lost everybody keeps telling me where to go

It may only get worse. Today the GOES-12 satellite recorded the most intense flare ever measured and simply went past the max measuring capability. The associated solar radiation storm is following. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Jim, put simply the difference between NAD83 and WGS84 is really not an issue so supporting BOTH (NAD83 & WGS84 if that’s what you meant above) as far as transformations/conversion from/to NAD27 for geocaching is really not warranted. And for sure there’s more than enough difference between WGS84 and NAD27 to require appropriate translation but NAD27 being the confused hybrid it is, straight mathematical conversions aren’t really suitable anyway and all this has to do with the underlying data sets and adjustments over many years. Also that “meaningful piece to the puzzle”, “spheroid” is a more appropriate definition than “ellipsoid”, according to the OED definition anyway. In any case the spheroid on which GPS is based had to be determined first and the IERS have been refining a global datum ever since. WGS84 was modified and changes made to GPS in 1994 to be coincident with ITR92. Any spheroid is determined based on/from physical points, just that’s it’s much more complex to do this for global datum purposes than a simple local definition. And yes, what most commonly call a DATUM is the geographical coordinates, namely latitude, Longitude referenced to the surface of the spheroid. So if we’re talking about datum’s then the WGS84 datum does include geographical coordinate sets but if we’re referring to the WGS84 spheroid, hic ellipsoid (which is in fact based on the GRS80 spheroid except for f) then that is different and this is where technically the NAD83 & WGS84 datum’s could be thought of as different even if they were based on the same spheroids (which they aren’t). Users work in datum’s not spheroids and there’s several examples in the world where different datum’s use an identical spheroid yet the coordinates are many metres different. So with a common spheroid any conversions/translations between these “datums” are based on the underlying data sets in conjunction with the spheroid/s but not simply the spheroid only. Any good conversion/translation between GPS (WGS84) and NAD27 should be done using NTv2 distortion models as NAD27 data sets are not what one would call homogenous. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The differnce between NAd83 and WGS84 is of little significance for practical applications and certainly as far as geocaching is concerned it's simply not an issue. In pure ellipsoidal compuational terms the difference is around 0.0001 metres so even for most surveying purposes is of academic interest only. However one should look at NAD83 and WGS84 as being independent of each other as they are basically based on different points (mainly), different observation data etc. This different base coordinate information then gives rise to any difference in physical coordinates much more so than any differences in ellipsoids. Cheers, Kerry. I never get lost everybody keeps telling me where to go

That latest storm warnings have issues with ionospheric disturbances 100 times worse than normal and for GPS users in the thick of these possible disturbances there might be some issues with the performance of ionospheric models. Even WADGPS such as WAAS won't handle these types of ionospheric disturbances well (if at all) at all and from some reports compass behaviour in parts of Canada is eratic to say the least. Cheers, Kerry. I never get lost everybody keeps telling me where to go

ALL WAAS receivers regardless should have a clear and concise user friendly ON/OFF option instead of all this underhanded undocumented secret service stuff. Really what's the big deal it should be a user option, pure and simple. Magellan undocumented codes Cheers, Kerry. I never get lost everybody keeps telling me where to go

"Discrepancys", 2.5 mile would/could/might be considered not normal? Depending. I suppose some other questions might be, Which GPS?, What user configurations are allowed (and what is it set to) for things like distance, speed, trip meters, track points etc etc? How long did this hike take? How was the GPS carried on this hike? In pack, in pocket, in hand (swinging or still), The certainty tat Sat lock can be guaranteed for the "entire" hike? Another thing to think about is a stationary "fixed" GPS over a period of time will in fact physically not move but the track will show distance "travelled". These days with SA discontinued that "distance" can be around the 3-5 miles per 24 hours (depending). Cheers, Kerry. I never get lost everybody keeps telling me where to go

"Estimate" as in "E"PE or "guestimate", yeah basically the same thing, doesn't really mean anything in absolute terms. With both being "estimates", I wouldn't get to optimistic with either of them being better than the other. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by fizzymagic:.... I know that none of the current crop of Garmin or Magellan units do so. Now that's probably putting it a little more in perpective as saying ALL receivers go to the full extent of velocity vectors and freq drift is perhaps over doing things just a tad. Not all recivers out there are the current crop and also there's a few more manufacturers than just the limitations of Magellan and Garmin and even in those camps there can be quite a bit of difference between models. The computing power to determine redunancy in position/time as well as 3 Dimensional velocity vectors plus freq drift for a possible 12 sats as well as do all the other bits and pieces and general house keeping is quite staggering and really in many of the cheaper units there's simply not the capacity. That's not to say that many don't go part of the way to determining velocity vectors using doppler shift principles but there's also other data involved as well to streamline usefull output to accuracy typical of a recreational handheld. But until some of these manufacturers actually make their code available (and that's not going to happen) then just like EPE and FOM, the exact propriety methods used to determine some of these parameters will always be a little subjective and assumptive. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Clouds haven't seen too many of them be an issue with GPS mainly because they aren't an issue, really. Cheers, Kerry. I never get lost everybody keeps telling me where to go

All these things could happen, which is why there's some dedicated earth stations and agencies that monitor these types of things. In many ways it's more a warning to be aware of these things when planning critical type missions as really if one looses lock while caching it's really not the end of the world. GPS satellites have done pretty well considering previous major CME eruptions. GPS satellites simply have a bad habit of not curling up and giving up the ghost. Some ways that's a good thing but in others it simply takes longer to get the next generation into space. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by fizzymagic:Completely and absolutely incorrect. As I wrote above, the velocity is _not_ calculated from multiple fixes. no I wouldn't call it completely and absolutely incorrect as this method is exactly what some (many) recreational units use. There's certainly other things using GPS and Doppler shift in the carrier signals but I wouldn't think that this principle is used in ALL recreational units for velocity calcs. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One could probably imagine there will be some comparison differences comparing cable drive speedo to GPS speeds. However with GPS speeds the error is relatively constant (for the same point in time) at most speeds but the % error can be considerably different. At 5mph the the % error could be as much as 20%, where as if doing 60mph the % error could be 1 or 2% (generally less), which isn't a big drama if all things are considered. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Range rate error (that will affect speed type calcs) even in the days of Selective Availability was really very stable at approx 1km per hour. Basically a "non moving" GPS would on average move 24km in 24 hours. Without SA range rate errors are really very stable and big jumps in subsequent positions doesn't really occur unless there's specific interference or obstruction issues. Without SA range rate error is in the centimetres per second bracket and of little impact on GPS speed. Cheers, Kerry. I never get lost everybody keeps telling me where to go

"automatic magnetic declination" is purely based on predictions and with the north magnetic pole wandering 40 odd km west each years and arounbd 80-100 km round in circles in any one day these predictions can change. From time to time most manufacturers will release software updates, which contain updated declination tables as even predictions change over time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Doesn't sound like a problem to me. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Some might ask, who is Ivan A. Getting? Ivan Getting basically conceived the global positioning system and was the visionary behind the system we now know as GPS. Getting and colleague Bradford Parkinson were awarded the Draper prize in early 2003 for conceiving and developing GPS. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by x_theory:Kerry, Could you tell me how I'd go about figuring out which version of the 4000XL I have, and if it's a true 12 channel parallel, rather than a two 2 channel parallel reciever? Thanks! As mentioned above that's about all I know about them. Check the satellite strength display and nore the type of information displayed and the location of the North indicator. quote:The full 12 channel receiver apparently has 2 different signal strength screens, one with a bar graph and the other is a numeric version. The North indicator on the full 12 // channel version is in the upper right hand corner, while the 2 channel version the North indicator was in the upper left hand corner and doesn't have the bar graph display. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by ChiefPig:Sounds like this is the Canadian equivalent to the existing DGPS in the states. Not really the equivalent of WAAS. I think DGPS has existed in the U.S for a while now and is being mainly used by ships and other water vessels. It's partly WAAS like (probably more WAAS like than DGPS), in that it uses a combined network of ground stations to a central command, then transmits those corrections via geo stationary satellites. The satellite re-transmitted corrction data (to this point it's basically a mirror of WAAS) is then received by a "special" receiver (unlike WAAS but closer to DGPS beacons), which converts the corrections into standard RTCM type corrections, which are similar to what USCG type differential stations transmit via radio beacon. Really it's central primary workings is Wide Area Satellite Differential "similar" to WAAS. DGPS (as per USCG) is radio transmitted based on a single ground based refernce station but the U.S have been in the process for some time to expand this "conventional" ground based augmentation system on a national basis and is a joint national transport project not just coastguard.. US National Differential GPS Olar, no it's certainaly not something the normal cacher would require but it's becoming interesting the different track different countries (even ajoining countries) are taking to improve affordable cost effective accuracy, might even be classed competitive accuracy? Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by IVxIV:.. the problem was (I think) that while the 4000XL is a 12 channel receiver it isn't a _parallel receiver_ .... The 4000XL was not necessarily a 12 channel receiver as there were 2 different versions of the 4000XL and they both looked the same. The real 12 channel version of the 4000XL was a true 12 channel parallel receiver, then there was a 2 (two) channel parallel model that could/would scan up to 12 satellites. The 12 channel receiver apparently has 2 different signal strength screens, one with a bar graph and the other is a numeric version. The North indicator on the 12 channel version is in the upper right hand corner, while the 2 channel version the North indicator was in the upper left hand corner and doesn't have the bar graph display. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Canada has now announced it's differential system, which is similar to WAAS in being satellite differential but produces RTCM correction data. Canada's Satellite Differential system One difference is it will "cost" as one will require to purchase a special receiver, which can be connected to ANY GPS, which is Differential ready. With this receiver further useage is free with no ongoing subscription costs. This may be the way of the future as WAAS is an extremely expensive system, which few countries can afford anyway, yet still require differential service capabilities at an affordable cost Interesting that some manufacturers have dropped differential ready options from some GPS receivers, which of course now will exclude any of these from being used with this type of service. The level of accuracy provided with this system will be dependant on the users actual GPS equipment and the cost benefit will be relative to actual accuarcy required. For caching probably not all that useful relative to the cost but the option is there for anybody that wants (needs?) it. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The north magnetic pole is a bit of a funny one but considering the distances generally involved its erratic behaviour isn't a major issue. Generally the north magnetic pole is moving about 40km west per year but in any one day it generally wanders around within a 80-100km circle. ".... but does that mean consumer receivers are now JUST as accurate as miltary ones now?" On a comparative basis one would be hard pressed to really find any critical difference in straight accuracy using SPS. But just like some civilian systems augmentation systems are also used in some military units and military units have additional "things" to prevent "interference" etc. The main advantage with dual freq units is that atmospherics can be determined in real time where as single freq units (including single freq military PLGR's and recreational/civil units) have to use modeled atmospherics. The new dual freq military DAGR (PLGR replacement) unit will have much more capability than the old PLGR. But then the DAGR is much more than simply a GPS. ".... does that mean if for some reason the GPSr did not obtain the correct declination, or if it was manually put in incorrectly, that you'd still arrive at your location eventually, but your directional indicator may be a bit off key?" That's about it, the destination point wouldn't change but in the process possibly the bearing to waypoint, course over ground values etc might not be relative or meaningful to say your compass etc. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:.... Since I know accuracy of civilian GPSr's vary quite a bit from military pluggers Without SA that's Not so. quote:.... having an accurate declination setting is paramount in making sure your coords are as accurate as you can get with selective availability What does selective availability have to do with things these days, it's been discontinued for over 3 years. Also what has declination have to do with coords derived by a GPS, there is no connection. Declination is relative to bearings/headings etc not a single position. quote:.... or even elevation settings for that matter, too. what about elevation settings? Cheers, Kerry. I never get lost everybody keeps telling me where to go

Being one of the built-in car systems most also have inertial as part of the system as well. The micro inertial systems are only about 1/2" square but extremely accurate and included in these car systems to handle the obstruction issues in the urban canyons where GPS reception can be obstructed most of the time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by StarshipTrooper:Commercial vs consumer grade...it couldn't have anything to do with antenna size and/or highth, could it? I mean - those things ain't stickin' way above the backpack (or tripod) for nothin'. Not so much the size but basically more the design and purpose. Many high order receivers are dual frequency and that requires an antenna capable of receiving the 2 freq plus some other refinements. Height has all to do with a clear view of the sky at all times without obstructions and this principle apllies equally to ALL GPS receivers/antenna's regardless of the purpose. When there's no obstructions it would basically work just as well flat on the ground much like this everybody keeps telling me where to go