Kerry.

quote:Originally posted by Tony and Charlotte:.... Could it be Uncle Sam is messing with the satilites since the war in Iraq? No, No, No, No Cheers, Kerry. I never get lost everybody keeps telling me where to go

The GPS system certainly has that capability, which is what the "T" (Timing) stands for in NAVSTAR. However not all GPS receivers (as such) are designed to handle exact timing functions apart from what is used in range determination. The "Time" as displayed on most handheld type (and similar types) receivers is "close" but not exact as this time display function is of low importance in regards to processor priority. As a result of processor priority the displayed time can be about 0.5 seconds and up to 2 seconds out (and generally behind). Specific receivers that handle time functions are a little different to navigation typr receivers. As for daylight saving that's a people thing and in reality GPS time is different to UTC time from which time zones are applied and then silly DST on top of that. GPS time and UTC time are different (currently 13 seconds) as the earth is gradually slowing down. Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on January 23, 2003 at 02:57 PM.]

If the WAAS Geo is transmitting a "use for navigation" message then it can basically be used as part of the position determination just like the "real " GPS sats. I tend to get the impression that the Geo's at present can be a little unstable at times and probably don't get flagged for positional use all that much?. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GPSr's are "reasonably" clever in what they use and what they don't and has all to do with the logic, which is based on many factors, both broadcast and dynamically computed. Actually the 12 channel receiver was sort of a "mistake" as it was basically meant to be an 11+1 (somebody got the specs a little wrong) in which there was 1 channel, which cycled thru ALL the remaining satellites much like the 4+1 receiver did. Up until a short time ago 14 visible sats was a regular occurance (but not for any length of time). Just because a receiver has 12 channels doesn't necessarily mean it actually processes all data to all sats. Cheers, Kerry. I never get lost everybody keeps telling me where to go

"is this still a good unit?" will still basically do the job "Is it as accurate as the newer units?" under normal conditions there's basically no difference in accuracy that you will notice. "Are newer units easier to use?" No As for things jumping around? well that could be caused by many things, the unit, the location, surroundings or even a little bit of understanding in how to get the most out of the unit (any GPSr for that matter). As a starting receiver there's really not going to be any major disadvantage. Why not use it, get some experience with it while deciding which way to go. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Even though the system is good it's not 100% perfect (not much is, especially measurement type systems) as there are user and system issues that are basically un-controllable. One of the reasons why system specs are based on stats and relative to a certain %, as in the most common referenced 95% of the time etc. There are specs based even at the 99% (and 99.99%) but there's no 100% Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cachetrotters: quote:Originally posted by TeamCNJC:...and is usually at a 95% confidence interval. Does that make sense?... NO. 95% confidence level, the interval of which is approximately 2 sigma. (just causin' trouble--don't sweat it ) don Trouble so how about 1-sigma and 68% and we'll split the CEP value Since EPE is determined from the URA (User Range Accuracy), which is an un-measured "predicted only" quanity transmitted in the nav message then does that make the end result estimated or "un-predictable" Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on January 17, 2003 at 02:42 PM.]

From your description and comments a simple non mapping handheld is really where to start right now. Which one well there's many but of importance is whatever you acquire is that those who have to use them KNOW how to use them properly. A simple handheld will/can do much of the stuff apart from having advanced mapping and direction features and that's probably the direction to be aiming for but right now just keep it simple and include some training. I'm aware of emergency services who have sent rescue helicopters in the wrong direction (actually to the previous emergency site) as users have simply turned the GPSr on, not waited for a position fix, read off the coords (old ones) to the radio operator and simply dropped the GPS back in the vehicle. Some pilots generally have a tendancy not to solely take coords for granted (when dealing with different levels of expertise) but put those coords in context with physical features and might come back with something like "confirm that is approx XX miles south of wherever" as a check. These cases as above were a result of well meaning community groups who donate this type of equipment to the local rescue services but forget that there is some training required. A GPSr is not simply an "appliance" and requires a little more than plugging it in and turning it on. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cachetrotters:Not sure how someone could have a problem with an automatic averaging function, but I think the implication is that there is a problem with the GPSr. There are no problems with the Magellan averaging function. If there are, I beg you to provide credible information as evidence of such. Automatic averaging is just that automatic and one has absolutely no control over it and that can be an issue. There's no real issue with the GPSr just the averaging function, which leaves a lot to be desired as a practical function. An averaging function maybe (not that averaging is really a benefit these days either ) is ok as an "option" but not a function that can't be switched off. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by AdirondakMud:.... An entire set of twenty-five frames (125 subframes) makes up the complete Navigation Message that is sent over a 12.5 minute period. So would that mean that you should allow a minimum time of 12 minutes for a fix? 12 minutes for a fix? No. That 12.5 minutes is time taken to download a complete almanac and if the unit is used regularily then it's being updated all the time. Straight out of the box a GPSr should be left sit for that length of time and also if not used for some time so as to update the almanac. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Primarily be there at the best possible time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

It does sound like an aerial target for photography. These days with GPS there are not as many ground targets required as the photo centres (and other information) are correlated directly from GPS info connected and triggered by the camera. GPS doesn't really totally eliminate the need for ground targets but certainly reduces them by a considerable amount. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by AltDotAir:Bear in mind the waypoint for my house is very well-established, and I used two different GPSrs made by two manufacturers and they're both off by more than 400' for the first time (ever) in six months of use. The posted data for new caches is always suspect, of course, until verified, but it's when well-known waypoints get goofy that I suspect something is awry. == Alt Dot Air == With a Location, Date and Time the system can be checked, that's easy, no problem what so ever. From that one has some direction towards what is actually awry. Location, date and time Cheers, Kerry. I never get lost everybody keeps telling me where to go

System issues can be checked, just need an approx location (within a few hundred mile) and time of occurance. However more than likely some type of local anomaly (or user issue?) , which fits in the uncontrollable 5% (> 95%) of the user segment. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by welch:.... why is the system the Europeans are setting up going to be based on like 30 birds? Will that system have lots of areas of "overlap"? (simple answer please ) Another simple answer to Galileo is that there just might not be any satellites to worry about anyway. The Galileo program (at the moment) has appeared to have collapsed due to the unresolved differences of several of the partner countries. This issue was always one of the underlying unknowns as to how all countries were going to agree on the fine details required. One thing that really doesn't affect GPS (NAVSTAR). Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by BletchleyPark: .... LAAS (local area augmentation systems) are in development and testing for aproaches, landings and departures. Anyone have updated info on the development and testing of LAAS? I believe there was some formal testing in Canada ... anyone? I thought LAAS systems were already certified in the USA as Norfolk Island was the first internationally certified LAAS by the FAA. http://www.airport-technology.com/projects/norfolk_traffic/ Cheers, Kerry. I never get lost everybody keeps telling me where to go

Talk about shutting GPS down as we can do without navigation is just ONE function and not taking the overall context of what this thing actually is doing. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by the jackal1:.... if waas is not a once download for all of the correction factors, at least if i can download the ionospheric corrections factors and lose waas lock, isn't that better than no waas correction factors at all, if i happen to go behind an obstruction for a perioid of time, do i still at least have the partial correction factors available? If one takes a similar but opposite line to this, No iono corrections but Clock corrections etc (that is totally outside WAAS coverage) accuracy is blown out of the water by a huge factor compared even to standard GPS accuracy. Most differential systems will allow operation for a specified time but once the age of corrections becomes too great then the only safe thing to do is for the receiver to drop the differential mode otherwise the information and operation could become misleading. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cachetrotters:a whopping 22 megabytes! Thank goodness for cable modem... MP_win (Under Mission Planning) does exactly the same thing in a user friendly file size. The .ALM file is also available directly below the software link. The almanac file will only be as up to date as the most recent change/modifications to the constelation. http://www.thales-geosolutions.com/skyfix/gpsinfo.html Cheers, Kerry. I never get lost everybody keeps telling me where to go

There’s no mention of what type of receiver this is, how/where it’s mounted and what type of antenna system (internal/external) is being used. The whole space/user segments being dynamic events could occur at any time for what might appear no apparent reason. Heading north (dependent on the latitude), there’s basically a sky area (directly ahead) void of GPS satellites and the WAAS Geo’s are “behind” and depending on obstructions, interference, multipath etc then things can/will/do occur. Strange things is one reason GPS accuracy is based on a statistical figure (95%, 99% even 99.99% accuracy) as there is no 100% guarantee, with or without WAAS and especially as implemented in a handheld. As for “local area” considerations the ionospheric grid bands consist of 201 points on basically a 5 degree spacing (approx 550km). Each Geo can store/hold up to about 4 of these grid files if required. USA coverage (WAAS) spans 2 of these bands with probably only about a 20% (probably less) utilization of total grid points. Based on a 500 odd kilometer grid spacing it really shouldn’t be a problem for a GPSr to keep ahead of itself as far as ionospheric correction interpolating is concerned. However WAAS is not a load once use anywhere type system as not all corrections are position dependent such as the ionospheric corrections, which requires the receiver’s position to interpolate the grid. WAAS also relies on clock errors, ephemeris errors etc, which are specific to a satellite and not your location. Combined clock and ephemeris errors can be generally more than ionospheric errors. Clock errors can change rapidly and many receiver manufacturers are probably rather conservative in dropping differential (WAAS) corrections if all the “expected” corrections aren’t being received by the unit within a very short time frame (around 2 minutes in some implementations). Essentially there is no single source of error but individual sources of error, which are sent separate. The 2 WAAS Geo’s currently give WAAS basically no redundancy if either one fail and the system could probably become a 6 billion dollar white elephant for quite some time. Most recreational handhelds (most recreational units in general) don’t have the capability to fully support WAAS as far as alarms, integrity monitoring etc are concerned. WAAS was really never designed to be used in many of the environments (especially at this stage) that is actually being marketed. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by yorelken:Just saw a Canadian newscaster waving his GPSr around and talking about its virtues in the field and then saying something like " the Americans say they will shut the satellites down when they go to war just like they did in the Gulf last time." Anyone hear about that? One badly informed newscaster. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Doug Missy Mickey P:Geez, those GPSr programmers are pretty crafty people eh? Yeah, it's very cleverly (and simply) done and eliminates the need (and prohibitive expense) for precise clocks in the receivers. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by crr003:.... Before it locks onto sats, I switch to a view that shows the time (with seconds) and the lat/ long (Position page for Garmin). Now I watch the seconds - as they count up watch what happens when the lat/long fields go from blanks to a real position - the seconds will jump. (I think the longer the unit has been turned off the bigger the jump - internal clock drift). This coincides with the receiver switching from the acquiring sats mode to the 2D or 3D Navigation mode. For this discussion it is important to note the time changes with a 2D lock (I can confirm by going back to the Sat page and seeing 3 sats locked/2D Nav declared - I block half the sky with a building). So, if the time is being corrected with a 2D lock, isn't Kerry's description more correct, i.e. you do get time information from 3 sats? Probably what you are seeing here is GPS time, corrected for leap seconds both of which are part of and updated direct from the actual broadcast Nav message. This current UTC type time is then further changed by the user defined zone offset to give simple local clock time. Receiver display "time" is different to "timing" and "time offsetting", with the latter being part and parcel of each and every position solution. On recreational receivers the LCD time display is basically for convienience and since this has an extremely low order of priority when compared to the highest priority given to processing position etc. Generally the LCD time on most handhelds is late by between 0.5 to 2 seconds. Cheers, Kerry. I never get lost everybody keeps telling me where to go

I realize many here view GPS as simply a positioning system but the full name NAVSTAR GPS (NAVigation Satellite Timing And Ranging Global Positioning System) does a lot more than what is generally regarded as primarily a positioning system. However the pure "Timing" function of the system might explain some of the concepts of 2D and 3D positional fixes. Many of the pure "Timing" boards "generally" require a minimum of 4 satellites to calc the four unknowns (Position XYZ & Time) and of course in the real world more is better for redundancy. These pure Timing boards have one purpose and that is to provide an accurate time, which in some respects is ONE single unknown, which can be provided from 4 (or more Sats) to solve Position (XYZ) & Time 3 Sats to solve 2D position (XY) & Time 2 Sats to solve for EITHER X or Y or Z & Time IF any 2 precise values of the 3 values XYZ are provided 1 Sat to solve Time IF precise values are provided for X and Y and Z Generally the antenna's of these timing boards are permanently fixed so precise XYZ positioning can be provided if that mode of operation is required. This is generally not the best type of solution (based on a single Sat) but the option is provided as a function of many of these timing devices. All this gets back to the number of unknowns and minimum number of equations to solve for these unknowns. For every known value provided then one less obervation is basically not required (without taking redunancy into account). Cheers, Kerry. I never get lost everybody keeps telling me where to go

The sats have never been shut down and there's no reason it will occur with any of the conflict discussion at the present. Selective Deniability is an option but that doesn't shut anything down (as such) just denies availability and accuracy to the wrong party over a specified specific area. Cheers, Kerry. I never get lost everybody keeps telling me where to go