Kerry.

If the unit won't use WADGPS sats (WAAS, EGNOS etc) as controlled by the new software upgrades then it basically means you are outside the ground station network and limitations for using that particular augmentation system and probably should never have been using the system in the first place as accuracy can be drastically degraded. Cheers, Kerry. I never get lost everybody keeps telling me where to go

So many differences but just where and how does one explain somethings that some don't/ wouldn't/couldn't understand. From mm's to Tomahawks to FA18's landing on a carrier under full GPS control it's all explainable but somehow there will always be the distractors. Really mm static accuracy might fade into old hat stuff (and that's been possible for years) if one considers that a piece of metal (FA18) closing on a carrier's deck at X hundred odd knots, with a carrier doing X knots, with an angled deck along with the pitch, yaw and roll of both the carrier and the 18 and a pilot sitting on his hands while a GPS assisted navigation system targets a hook through a 3 foot virtual box 14 feet off the deck to hit a 2" wire. Now that's variable. As for Tomahawks being dead 1mm from the target point is still the same dead as being 30 metres from the target point. The results much the same, dead, but for many reasons Tomahawks or any of the JDAM's use a variety of navigation systems and simply don't rely on any one system. Besides the biggest problem with hitting something is knowing where it actually is in the first place. If one doesn't know exactly where something is then all the accuracy in the world will never hit it, without other guidance. As for so called "Survey Grade" stuff it's not so much the hardware (which is obviously different in several ways) but the way the stuff is used. The following is a SPS comparison between a $25,000 survey receiver and a $500 (lets call it) "Caching grade" receiver. The difference is really bugga all but then there's more to things than just SPS accuracy, with any "grade". everybody keeps telling me where to go [This message was edited by Kerry on October 08, 2003 at 08:24 PM.]

GPS v Galileo as usual a few chuckles in that. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cornix:So it's a kind of rounding error, why didn't you say this earlier? Rounding error some might call it a bug, some might also call it a stuff up as it simply shouldn't do what it's doing. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by skydog5:If the satellites have VERY accurate clocks, and the time signal is essential to navigation, and the satellite sets the time on the reciever, them the reciever knows the correct time and is not displaying it correctly. As was mentioned time (in this type of unit) is not a priority but also there is a major difference between what could be called "time" and "timing". As it appears it does have something to do with the particular receiver but one would expect straight UTC time to ok. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The clock time has no bearing on the capacity to navigate, it simply tells the time and nothing more. Telling one the time isn't a great priority for these type of GPS units as it generally worries more about doing other things. However 2 minutes isn't what one would call normal either and the leap seconds (13 of them) should be a problem either if handled properly. Generally when initializing a rough time is all that's required then the unit will adjust the appropraite/approx time from the navigation message and received data. 2 seconds can be normal but 2 minutes? isn't a system problem either. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The difference is basically the difference between the origins, effectively the 0,0,0 point of a figure with a specific radius and flatenning. NAD27 is basically a local datum based on a figure that best fits the shape of the earth over a particular area. NAD27 is much more variable and defined differently in different parts of the US. The following is basic (not what one would call technical) and based on specific Australian datum's, but the principle is the same and might show why there is a difference. Read AGD66 as NAD27, GDA94 as NAD83 and the shift difference in the States is much more variable due to many inconsistencies with NDA27. everybody keeps telling me where to go

Many of the current recreational GPS receivers output NMEA to 4 decimal minutes (able to be recorded) as NMEA doesn't specifically define any set number just that output is degrees minutes and variable number of decimal minutes. The whole underlying precision is controlled by the cartesian significant figures, what's displayed, stored, useable etc has a close relationship to this as part of the transformation/converion process. It's an interesting exercise in understanding some of the accuracy myths (including UTM) if one sets up 2 identical GPS receivers at a fixed distance apart (distance specific to the precision output available) and record/analyse the outputs. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Time zones need to be set manual. Cheers, Kerry. I never get lost everybody keeps telling me where to go

No point in turning WAAS off with respect a war in the Gulf as WAAS doesn't even work there and if there was a need to put WAAS into emergency military mode (as far as US coverage was concerned) then one might find some strange happenings with straight GPS. No nothing wrong with WAAS, operating normally since changed from test mode to normal operational mode on July 10, 2003. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Birdman (The real one):Hey Kerry, What are you doing over here? Been here for quite some time, trying to keep em honest Shall see what's going on at the THT next. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by cutsandbruises:yes I understand averaging. I read it on one of the FAQ pages. Thanks for your concern. And you still use it then? Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by cutsandbruises:I keep reading on the post about averaging waypoints to make sure the coordinates of a placed cache is correct. I understand that .... but are you sure? you understand averaging. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Bill, Repeatable accuracy (and Predictable accuracy) are no longer mentioned in any of the GPS signal specs. Certainly was relevent in the old days but appears no longer an issue. Back in 1990-91 (first gulf war) there were only 16/17 satellites in total and these weren't enough to provide 24 hours coverage even in the gulf. And yes the geometry still plays a part (to a point) in the accuracy, which is why accuracy is stated as a statistic and relative to a specific period of time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Appears your time zone offset needs setting to display local time. Those times would be UTC time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Definition of GPS accuracy. Positioning accuracy represents how well the position solution conforms to "truth". Truth is defined to be any specified user location where the position is known, within acceptable error tolerances and with respect to an accepted coordinate system, such as the World Geodetic System 1984 (WGS84) Earth-Centered, Earth-Fixed (ECEF) Coordinate System. Factors which affect positioning accuracy include geometry and URE variations unique to a given user location and the sample interval over which measurements are taken. So basically neither maps or waypoints are appropriate for determining the accuracy of a particular GPS over a specific period of time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

So many misconceptions with accuracy but understanding some of the basics then one wouldn't be questioning 3 metres but I question 3 metres as one certainly shouldn't expect that all the time either. There's no such thing as a absolute (perfect) navigation system but all things considered even 10 metres should be considered a blessing considered the mechanics of the system. As for CM accuracy it's not so much the receiver (but that certainly does help) but the way the equipment is used. Sure there's receivers that are capable of CM accuracy but this type of accuracy can be limited by distance and/or time. A so called $20,000 survey grade receiver is no more accurate when used in the same manner as a $200 handheld. It's more how $20,000 receivers are used that matters. Comparative military receivers do not do any better than many of the receivers used here and the Iraq war had no affect on normal GPS operations except probably be a little more stable as maintainence was kept to a minimum. But give it a few more years and dual freq recreational type handhelds will have an accuracy of around 1.5m, just that we have to wait for the civil dual freq signals to get into space. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Geodoggy:.... The degrees and minutes are the same on both. The seconds on the Meridian show 725N and 262W. The 310 shows 44N and 16W. Thoughts based on the limited info provided would tend to indicate that both units are not the same format. "The seconds on the Meridian show 725N and ..." there's no way 725N is seconds but being 3 digits and being 725 one might assume that is actually xx.725' (minutes). As per previous poster .725 minutes is 43.5" (seconds and rounded would be 44") and 0.262 minutes is 15.72" (seconds abd rounded would be 16"). So if the datum is identical on both then one might assume the 310 is set to Degrees Minutes Seconds format and if so would match your data provided. Also would fit with the capability of the 310's position formats apart from UTM are limited to Deg/Min.mm' (2 decimal minutes), deg/Min'/Sec" and limited to (2 digit) whole seconds only. But pay closer attention to how the position is displayed on the 310 screen, Deg/Min.mm will be for example 34^ 06.57' and Deg/Min/Sec will be 34^ 06' 34". Both those examples are effectively the same point just in a different format. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Not in any order of preference, use whatever you find the best. There's others but any of these will work. http://www.easygps.com/ http://www.gpsu.co.uk/ http://www.tapr.org/~kh2z/Waypoint/ Cheers, Kerry. I never get lost everybody keeps telling me where to go

Maybe UTM might give better results than using DD:MM.mm, maybe not? as perhaps the underlying precision of the coordinates could have some affect. If the underlying position format has some limitations then this would be reflected in any/all convertions and/or transformations Similar with units that can display better precision, even these units will not accept all UTM coordinates precisely as input as through the process of being converted from UTM to lat/Long to cartesian (cartesian being the fundamental GPS position format) then converted back to lat/Long then back to UTM some might notice that what was input is (sometimes) changed by the receiver. With some of these older units (some limited by processor and memory capacity) it's sometimes an unknown if the 2 decimal minute display precision is/was simply a case of that was all that was deemed necessary to output in the days of SA accuracy or limited by hardware in some other way. I don't have access to one but maybe someone with a specific fixed 2 decimal minute format output receiver (like a 310) who has got some spare time then try inputting an incremented (1 metre increments) range of UTM points and note what is echoed back to the display. Just curious. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GIS doesn't necessarily have to based on GPS locations. GPS is simply one of many tools available. Cheers, Kerry. I never get lost everybody keeps telling me where to go

So how many ways can a user stand around a handheld? think about it. So just how does one define "common usage". The difference between a user standing facing north or south can have a marked affect on the results. So many variables but many don't realise just what's applicable. Now why would anybody want to average and exactly how might that verify their coords Really there's many ways to improve having an "edge", planning is one of the biggest right down to which way one actually faces. Cheers, Kerry. I never get lost everybody keeps telling me where to go

John, so what your saying is that EPE and distance to waypoint have some connection? Actually I'm not all that sure why we have EPE (in any practical sense) as on just about every software version (even for different units) it can be different. It's interesting that you look at EPE and DTG as having some connection? Cheers, Kerry. I never get lost everybody keeps telling me where to go

John, I did realize what you meant from a firmware point of view and would query that a 0 feet display is actually appropraite. In reality a GPS can't (shouldn't) display 0 feet (regardless of ones location to the mark etc) as 0 indicates a perfect result and that's simply not possible. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Had nothing to do with the system (and certainly nothing to do with terrorist threats), which based on recorded data at USNO (approx 280k away) showed accuracy and satellites as expected, all there and all well. Cheers, Kerry. I never get lost everybody keeps telling me where to go