Kerry.

quote:Originally posted by Johnnyvegas:The time of day should not be an issue. Holding the GPS close to your body can be a problem. Using way point averaging can also be a problem if the person who hid the cache did not use averaging. Tree cover can be a problem. Time of day, no problem. Is that saying there's no difference between say 4 Sats, PDOP 28 and 6 Sats PDOP 2 and 4 Sats PDOP 2.3 and 8 Sats PDOP 6 etc etc as all those situations/events are possible given the right circumstances on any day. I'd be interested in your reasons why you don't believe Time of day can not be a problem. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Could also try this Simplied Time of Day explanation of what can/does/could occur based on system dynamics. However there's some real world variables that can't be included in an example like this. Cheers, Kerry. I never get lost everybody keeps telling me where to go

For sure time of day matters and what one is possibly experiencing is exactly what the system can/might/does do depending on the overall dynamics of the system relative to the location and the receiever being used. More satellites DOES NOT necessarily equate to better accuracy but with an over populated constellation compared to what the spec's are based on some peoples expectation will be really dashed if ever the number gets to what we are supposed to have. Consistency really isn't possible as the overall system is dynamic (satellites and users) but one can maximize to make the best possible use of what the system provides by being at where one wants to be at the best possible time, it's called planning. Cheers, Kerry. I never get lost everybody keeps telling me where to go

You mean the "Official answer" The technical answer only has a 95% probability. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The simple answer is NO. The long answer is No,No,No,No,No,No,No,No,No,No,No,No,No,No,No,No, Cheers, Kerry. I never get lost everybody keeps telling me where to go

A bit more on this perception that survey class receivers are CM accuracy. Well obviously they are are but it's more the method than simply being a "survey class receiever" Couldn't find the original (quickly) so appologies regarding the scan/image quality, however one should see the point. The "benchmark comparison" is between a $35,000 "survey class" receiver (Leica 399, 9 channel dual frequency) and a basic recreational receiever of the time (Garmin GPS45, single freq 8 channel MultiTrac). Note this was back in the bad old days of Selective Availability (~1997/98) but probably highlights the basic lack of much difference (in accuracy) better than even if done today. The 24 hour "average" accuracy was 19.7m (Leica 399) to 22.2m (GPS45) but this 2.5m difference in average accuracy (back then) was certainly not worth the additional $34,500 in this type of mode. But put 2 399's togeather in a static/differential mode or in conjunction with other dual freq static data and that's a different story. Cheers, Kerry. everybody keeps telling me where to go

quote:Originally posted by GOT GPS?:Our accuracy versus a surveyor's accuracy in centimeters. They will leave their expensive units going for awhile to average down to centimeter accuracy. I think that with trees overhead and moving satellites, that averaging can help. CM accuracy isn't something that comes about from averaging (per say). A "single survey class" instrument basically is not much more accurate than many recreational type units. However one will notice a slight difference but that has more so to do with refinements in the software (and technically the hardware). But a "single survey class" receiver can in no way achieve absolute CM accuracy by itself. Put 2 togeather then that's a different situation. 2 units can accurately determine the "relative difference" (in CM/MM) between them as each taking observations at precisely (and precisely it is) the same point in time has the capability of cancelling any error (put simply) as it really doesn't matter if the "absolute position" is of by say 16.172m/north at stn1 it is basically also off by 16.172m/north at stn2 (in simplistic terms). This "relative difference" based over a series of observations over a time period can be resolved to within CM/MM but one wouldn't call this an average (as such). ON a single baseline the end result of the unknown/required station then will only be as accurate as the coordinates of the known station. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Red Barron:If you want to get into how accurate a GPS is goto Dave Wilson's site or talk to a surveyor that uses the $70,000 units. You will come away with the idea that if you can get with in 50' you are doing great. Not to sure what your trying to say there?. What "type" of GPS are you referring and in what mode of operation. NO surveyor buys $70,000 worth of gear to expect with 50'. All have some "limiting" factors. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, well just recently there's some certain Garmin software updates that actually have auto averaging (just like that other mob ), which is totally different to the normal user selected averaging, which at least gives users the option to or not. What get even more annoying is Garmin's lack of any reply to queries about this software update, actually Garmin has NEVER replied to any query I've ever put to them. Cheers, Kerry. I never get lost everybody keeps telling me where to go

There's nothing wrong with the 12 at the right price but take into account that they are basically superceded technology (actually several times over) when determining a reasonable price compared to more recent technology. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by John E Cache:I assume you talking about the digital message from the Naval Observatory. Are you saying that the GPS units receive leap second information from the satellites too? Or do the GPS manufacturers program the GPSs with the current count since 1980? No not directly from the Naval Observatory but from the actual Navigation message transmitted from the Sats. This information is uploaded from the GPS control centre. "GPS Time" hasn't changed since 1980 but UTC effectively has since the earth has been slowing down so leap seconds are irregularily required to keep time ("earth time"). It just so happens that all leap second adjustments since 1980 have been positive but they could have been negative (if the earth started revolving faster). GPS receivers are programed to read the leap second adjustment from the Nav message and make the appropriate adjustment to GPS time to current UTC time then the user sets their time zone to display local time. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One thing with a carrying a handheld is always try and face the equator as there's basically no satellites over the poles and if your facing the poles then the sats (most of them) are behind you and you become an obstruction. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by John E Cache:GPS's are on a free running atomic clock that isn't adjusted for leap seconds. The GPS time is 13 seconds off. I don't know if the GPS units adjust the time accordingly. The leap second difference is also part of the Nav message and GPS receivers do take that into account when determining "current" UTC time. GPS time = UTC time @ Jan 5/6, 1980. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Maybe someone can clarify why there's any need for Zone letters for pure UTM as opposed to "Grid References", which are a little bit of the zone number, zone letter, and only a part of the full UTM coordinates. Ok Grid references are different but UTM is really controlled by the zone number alone as UTM can not be negative and hence has false origins in the southern hemisphere as the northing is not directly measured from the equator but a point 10,000,000m south (and 500,000m west of the CM. UTm might be nice for some applications but one thing is for sure at least Lat/Long is basically unique (no confusion ) Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Stunod:Your GPS, once it has locked onto the sats, is probably the most accurate clock you'll ever see. It is constantly corrected by atomic clocks on the sats. It certainly has that possibility but generally since the time of day function has nothing to do with other more critical functions of the receiever, the CPU doesn't pay to much attention to constantly monitoring parts of the Nav message. The time display "in general" can be around 0.5 seconds (sometimes up to 2 seconds) behind (generally always behind in recreational type receivers). It's close enough but not perfect. Cheers, Kerry. I never get lost everybody keeps telling me where to go

One and/or all of the following general possible local anomalies, obstructions, interference, multipath or the other 5% Cheers, Kerry. I never get lost everybody keeps telling me where to go

How fast or slow do you need it to be Cheers, Kerry. I never get lost everybody keeps telling me where to go

Your 18S and/or 18N, if the N/S is trying to indicate the hemi-sphere then maybe check the latitude sign of the software as some software packages allow the latitude sign to be ignored and maybe there a toggle in there somewhere which overrides signs and simply assmumes (by default/user setting) N or S. Cheers, Kerry. I never get lost everybody keeps telling me where to go

GPS altitude, take it for what it's worth but if it appears close (closer than it should be) then it's more good luck then anything else. Cheers, Kerry. I never get lost everybody keeps telling me where to go

It's really not a triangulation problem at all but trileration or best described as Resection by distance and very similar to what GPS does. It's relative easy to do but harder to actually (try to) explain but it's basically the (over determined solution of) intersection of circles. The centres are the given coords and the distances become the respective circle radius. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by blindleader:True, but somewhat useless as advice .... It's a great idea but I don't know how to go about doing it. Useless? well that's what planning and especially GPS mission planning software is all about. How to go about it? that's easy, use some mission planning software, several free versions available. quote: Averaging at a site for a long enough period for the satellites to move significantly is a method which you could actually apply reliably. Reliably? how do you know that. What is significant movement as one also really doesn't know if the geometry is actually improving or simply getting worse with time. As has been said many times before Averaging bad data simply gives a bad data average. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by opey one:Actually, old fashioned and conventional instruments are not used underground anymore. We have engineers who use transits and "spad up" at least once a week. With relation to GPS systems they certainly are conventional. If a "Transit" is not old fashioned and conventional then what is it? Cheers, Kerry. I never get lost everybody keeps telling me where to go

Can't emphasize enough that being at a certain location at THE RIGHT TIME is by far much more important than any averaging scheme/thinking of any sort. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Well April 1 has come and gone, so who is going to be stupid enough to continue with this crap. Honestly has one ever heard so much tripe! Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by trailkat:Hmm...I am wondering if Uncle Sam is scrambling the GPS signal over Iraq or not. There's been no indication of that. quote: .... I wonder if the accuracy would be equal to the days of S/A or would it be less accurate? SA is a variable thing and as far as is known, if it was on it can be cranked up to something like 2000m (at least?) as required. quote:I think I read somewhere once that the Garmin GPS12's used in the survival vests had been modified to understand and use the military's GPS signal I'd doubt that and in any case if that was so then it's simply no longer a GPS12, at all. Cheers, Kerry. I never get lost everybody keeps telling me where to go