Pajaholic

Since you didn't use a smiley or "<FE>" (irony) tags, I have to assume that you're serious. My office is in a single-storey building and its roof has proved less of a hindrance to GPS signals than the trees in my area, I thought that doing the test in my office would be a better than fair comparison to how things would be "in the field". Put it this way, I don't intend climbing into the upper branches of the trees over a hide to get the co-ordinates! You're looking at that with the benefit of hindsight. You know where GM says the waypoint is because I've indicated it with a large, red dot. Remove that and it's not immediately obvious that the top-right pair are anomalous. Without knowing the actual location, I'd probably discount the bottom left pair and the top-right singleton (greyed in the image below), leaving a reasonable group of four. The average of those (guestimated by the blue dot) is almost 5m (16ft) off. Of course, used with the benefit of hindsight (i.e. knowing the GM co-ords) the four closest points average to pretty close agreement with GM and thus they corroborate each other. So I guess that's the way to go. Geoff

Strange you should suggest that - I found your post when I got back from doing such a test at the local park. I used the end of a park bench (larger red dot) that runs roughly N/S in the following plot and took fixes (smaller black dots) after approaching the park bench from 1, 2, 3, 4, 5, and 6 o'clock. Now this was under ideal conditions with the GPSr able to track 7 or 8 satellites and with HDOP less than 2: All I'm trying to do is find a way of giving co-ordinates that that would be acceptable to me as a finder. The testing has convinced me that my GPSr isn't accurate enough to obtain co-ordinates on its own, so I need to use a hybrid method or wait until I have a better GPSr. Anyway, as you suggest, it's not worth me getting het up over this and I just need to post what I believe are good co-ordinates. Thanks. Geoff

Thanks for that. However, the potential for the co-ords I give to be up to 10m (33ft) off worries me - especially since every cache I've found to date has been within a foot or two of where GM says it should be. Since my last post, I've found the national grid references of some of trig points near me. The site I got them from says these were obtained by conversion from WGS84 co-ords and subject to conversion error. Also, 5-digit grid references are only good to the nearest metre and my use of GSAK to convert them back to WGS84 co-ords is likely to induce further error. That said, the trig points at the corners of a quadrilateral enclosing the area in which I'm likely to hide my first few caches are all within five or six feet - as the satellite images below show! To be that close despite the potential for error seems to be adequate confirmation that Google Maps is accurate in my area. However, I'll still wait until I've a few more finds before making my first hides. Geoff

Thanks for your advice. I tried this for a point on my office desk taking 8 averages, each done over between five and ten minutes using the averaging function of BeeLineGPS. The following image shows the results of the 8 averaged co-ord sets plotted on Google Maps represented by a black dot and the actual location according to Google Maps shown as a larger, red dot. I've also included a scale (measured on the ground and transposed to the plot). Note that 5m is over fifteen feet and HDOP was between 1.5 and 5 during the test. IMO, even averaging the averages isn't good enough! If I'd have used GPS alone to obtain the co-ords, the average of the averaged co-ords would have been about 5m off and if I'd just used the first obtained (i.e. the one lower-left of the image) it would have been about 10m off. I feel the need to check GM accuracy in my area with a definitive reference. I thought of using an OS trig point since my area is shown on GM in enough detail to just about be able to pick out the baseplate from a GM image at maximum zoom. However, the Ordnance Survey no longer maintain these and suggest in this page that OSGB36 trig points should not be used as GPS control points as only low accuracy (WGS84) co-ordinates can be obtained from them. However, the accuracy they're talking about for GPS surveying using ETRS89 is to the nearest 5cm (two inches), so I suspect that a check of a converted 10-digit OS grid reference against GM's satellite imagery would suffice! Other than that, I guess it's a case of waiting until I have enough finds to be able to say with some surety that GM is or is not good enough to use for the primary fix, and hence whether I only need use my GPSr as a check and to demonstrate that it's possible to navigate to the cache using GPS alone. Geoff

In my area, the registration seems to be very good. However, I've limited experience so it's too soon yet to say with surety that GM is spot on across the areas where I'm likely to hide caches - but then I intend waiting until I've got a few more finds before making my first hide. I guess that it's a matter of interpretation. The requirements actually state: To me, this imposes two requirements: You (personally) must visit the site; and You must use a GPS to at least verify the co-ordinates. Note that the requirements don't call for you to obtain the co-ordinates using GPS alone and, pragmatically, I suspect that the requirement is there to ensure that the cache can be found by GPS so, for example, it would rule out placing a cache deep within a cave system where there's no GPS signal. In my case, I'm suggesting that I go out to the site on more than one visit and use my (known to be inaccurate) GPSr to obtain several fixes per visit. I'll then plot those on Google Maps. If they surround the co-ords obtained from GM then I'll consider the GM co-ords to be the best estimate even if it doesn't coincide with the average from my GPS fixes. IMO I'll have followed both the letter and the spirit of this requirement because I'll have used a GPS during the process of obtaining the co-ordinates and I'll have demonstrated that it is possible to navigate to the cache using GPS alone. The alternative IMO is that I don't make any hides until I've obtained a better GPSr, which might not be for a year or two (if ever), and somehow it feels wrong not to give something back for the wonderful places other cachers have taken me. Geoff

Well, I did mean seconds when I said minutes, so my bad there... But if you're using GPS to record the coordinates, and GPS to find the coordinates, then it wouldn't be an issue with finding something -- that problem should only arise if you're posting coords from Google Maps and trying to find with your GPSr, or vice versa. The problem shouldn't arise since (AFAICT) both GPS and Google Maps use the WGS84 standard and hence both are "off" the "official" prime meridian by about 5 seconds, which is about a hundred metres at London. Provided the means of hiding and finding use the same standard (i.e. WGS84), there should be no problem. Issues should only arise if the methods of hiding and finding didn't use the same standard or if the satellite/aerial imagery isn't precisely overlaid. However, both do use the same standard and if you have good evidence that alignment is good in the area you're looking at, the chances are that Google Maps can give as good (if not more accurate) WGS84 co-ordinates than a typical geocaching GPSr. Geoff

After reading an interesting bit of history on the Prime Meridian, I would likely never use Google Maps (nor any of the other map sites) again for caching coordinates, as it appears all will be consistently off by 5+ minutes of longitude (unless I'm totally misinterpreting the referenced article) when compared to your GPSr's coords. It depends on which datum co-ords are based upon to what accuracy AFAICT. Again AFAICT, both Google Maps and geocaching co-ordinates are (or should be) based on WGS84 whereas the 0° longitude Greenwich prime meridian (GPM) is the basis of another system. IMO it's not surprising that two systems that are derived differently are not exactly aligned even if they do use the same units of measure. FWIW, Google Maps (GM) has consistently been spot on for all of the eight caches I've found to date whereas my GPSr has not. From this (albeit sparse) evidence I suggested that using GM in my area to fix the co-ords for any hide I might make would be more accurate than relying on my GPSr. Now edscott wrote that there is a blanket ban on using GM this way, but since there seems to be an acceptable practice of tweaking co-ordinates I infer from edscott's post that should the tweak align the co-ords with GM that would be "happy coincidence". IOW, the tweak would be to improve accuracy, not to add difficulty.

I have two objections and so vote "no": 1. Benchmarks are not geocaches and belong over on Waymarking.com IMO with all the other interesting locations that are not geocaches. 2. Benchmarks are country-specific (i.e. USA only), so most of the World can't participate and it thus seems unfair that they should be "lumbered" with a zero score than's none of their fault. Geoff

Provided there is a trail there are usually identifiable landmarks. For example, my second find was GC136Z9 - Death Corner. My GPSr was completely useless for the last mile and a half and I could have got to where my device lost the signal using a basic road atlas! The cache is in a deep valley in a forest (i.e. a rural area). I got to it by checking bends and junctions in the trail. The final find was by bearing and distance from the nearby junction. This process is much harder if you don't know how distances on the aerial photo relate to distances on the ground - which is why I said to include the scale on printouts. FWIW, even trees and bushes can be identifiable landmarks. For example, my third find was under trees in a park and although my GPSr got me within 100' it lost signal when I got close to the cache. I resorted to triangulation from a pair of bushes and a small tree, which led me to within a couple of feet of the cache. With that said, I've now got 8 finds (all in rural locations except for the above park) and of those only two would have been more difficult with Google Maps than with GPS. From my experience, I suspect that you'll be able to tell from the satellite image itself whether it can get you to the cache - and thus know which ones to leave until you have a GPSr. HTH, Geoff

I've just started myself. I already had a GPS-equipped PDA. However, for two of my three finds to date I had to rely on satellite imagery and triangulation from identifiable landmarks. From my experience, I suspect that a reasonable compass and a printout from Google Maps etc. (with scale included) will be all you need for a good many caches. If you enter the co-ords into the Search box of Google Maps, you can get an aerial view with the co-ords prominently indicated. HTH, Geoff

dino-irl, thanks for that. Until this thread, I didn't know the names of any of the reviewers - or that there was only one per area. However, following your advice I see that Graculus is my reviewer, so I guess I need to find out which method he prefers. Thanks again, Geoff

Thanks Deci. You say that both are possible, but I can't see how to contact a reviewer to iron out issues prior to submission (i.e. without submitting a new cache form). So I guess that the best thing to do is to submit all caches of a set with a request in the notes to reviewer that each is reviewed for issues only and not published until all issues across the set are resolved. What I have in mind is a set of three. The third is a mystery with co-ordinates and hints contained in the first two. What I don't want is for one or two of the set to be published and for the other(s) to be refused, since I'd then need to withdraw the published cache(s) and re-plan. This is why I feel the need to know (at least in principle) of any "showstoppers". Thanks again, Geoff

Thanks for that since it almost answers a question that's been niggling the back of my mind for a week or so. I have a couple of sites in mind but there might be issues (e.g. proximity to military facilities). Would you recommend submitting for review for issues only, or is it possible to iron out any issues with a reviewer prior to formal submission? TIA, Geoff

In UK, roads are classified as A, B, or "unclassified". A & B roads are normally fine for HGVs. However, you need to exercise caution if you're going to take a truck down an unclassified road since such roads could well become unsuitable. Thankfully, most such roads have width limits, height limits, or warn of other issues (such as hump-back bridges). Some have signs that categorically state "unsuitable for large vehicles". Despite these warnings, people still blindly follow their sat navs and get stuck. To my mind, that is driving without due care and attention and deserves prosecution.

Sat nav has become the bane of some villages in the South Hams, Devon, UK. There is only one major road through the area suitable for heavy goods vehicles and that road is often congested or blocked through RTCs or road works. So when drivers hit the "divert" button, sat nav sends them down roads that are inappropriate for the size of vehicle. Those trucks then end up blocking the only road through a village as either opposing traffic or the truck is obliged to reverse long distances (sometimes back to the main road). In one case a few years ago, one HGV grounded out and got hung up on a hump-back bridge. The only road to the village from that direction was closed for about a week until they could free the offending truck. Perhaps they should prosecute more motorists for blindly following their sat navs when common sense says they should think twice!

Mine will display all 6 decimal points when used with something like BeeLineGPS (I have a SiRFstar-equipped PDA), but it's making claims it can't keep and the last two or three digits have a merry dance even when the device is still. On these forums I recently saw the owner of a Garmin GPS 60 write that his GPSr was up to 40 ft off - so it seems that even some dedicated GPS devices have the same issues. I understand that the newer Garmins have much more sensitive receivers. I'd love an eTrex H and guess it'd be a worthwhile investment just to be able to get a fix in woodlands. However, I suspect that it won't be more accurate than my current device in the open. Geoff

I'm a newbie, so please go easy on me. I'm a concerned geocacher - but how accurate is "accurate as possible"? I ask because my own GPSr is hideously inaccurate and, like some others I've read about in these forums, can be off by as much as 40ft. It's also next to useless in the majority of likely cache hiding places I've spotted since they're under trees. My plan is to fix the co-ords using Google Maps and verify those co-ords are roughly in the right place using GPS. I base this on GM being spot on for all three of my finds to date - and since two were under trees, I made those finds from GM and triangulation from identifiable landmarks rather than GPS. Actually, the more I think about this the more the question, "How accurate?" niggles. Geocaching.com gives co-ords to six decimal places of a degree, which implies a precision that I suspect few geocachers can achieve (6 DPs implies "to the nearest 10cm or 4in"). IMO five decimal places would probably be more reasonable (i.e. to the nearest metre or yard), but I suspect even that's pushing the accuracy of most budget GPSrs. For example, I did an averaging test over two days, four visits, and sixteen fixes. For all fixes, the HDOP was between two and five and the test waypoint was the end of a park bench in the open. The averaged co-ords were nearly 3 metres (10ft) off where GM Satellite view says the waypoint actually is. What I'm trying to say is that I'll be as accurate as I can when giving co-ords for any hides I make. However, the precision the cache page will imply is certain to unreasonable and I'll consider I've done a good job if the co-ords fetch up within a couple of yards of the actual cache location. Geoff

Thanks Marky. Two finds made. However, the PDA was about as much use as a chocolate fireguard for the second. Both were in woodland, and for the second the PDA couldn't see the satellites for the trees and I couldn't get a fix for the last mile and a half to the cache. Thankfully, I'd plugged the co-ordinates into Google maps and printed off some aerial photos. Google maps was spot on. Even if that felt like cheating, I'd walked the five mile round trip so I didn't feel too bad about signing the log! Geoff

Thanks guys. I installed the "GPS Instant Fix". It took half an hour or more to get the first fix out of the unit after doing the update and the reported HDOP seems to have increased, but now TTFF seems a lot quicker so I suspect that accuracy might improve also. Since I made my OP I've spotted that some owners of dedicated handheld GPS units report similar accuracy to my PDA, so I guess that Indotguy is spot on. It just seemed to me that if my GPS was up to 40ft off and that was typical, once I'd got the minimum distance reading I'd potentially need to search a circle of diameter 160ft - which seemed huge considering the accuracy implied by the co-ordinates that geocaching.com provide. After a little research, I conclude that lat/long co-ordinates to six decimal places imply an accuracy that just isn't possible with the sort of devices that geocachers use. AFAICT, six decimal places implies an accuracy of about 10cm, so surely five place (i.e. an implied accuracy of approx a metre) is more reasonable. That said, I guess that attempting to find a few caches will be the acid test. My wife and I are off caravanning this weekend. I've loaded details of a few caches near the campsite into the PDA and hope to make my first finds. Thanks again, Geoff

I'm an absolute newbie who's yet to attempt his first find and who hopes to be able to use his current PDA for geocaching. The PDA is a Fujitsu-Siemens Pocket Loox N520, which has a built-in SiRFstar III GPS receiver. To this, I installed an evaluation copy of BeeLineGPS and ran some accuracy tests. Test 1: Get the co-ordinates of a known landmark from Google Maps, create a LOC file with those co-ordinates and import to BeeLine. Take dog for walk to check whether the GPS would accurately direct me to the resulting waypoint. Result: The least distance from the waypoint shown was just over 3ft when about 12ft away from the waypoint. When stood over the waypoint, the GPS claimed I was about 15ft away. Test 2: Create several waypoints of the same point, moving away from and back to the location between each. Result: According to Google Maps, the closest waypoint was about 4ft off and the farthest almost 40ft off. Test 3: Create several waypoints with the back of the hand holding the PDA on the same point and without moving between each. Result: Roughly the same as for test 2. I'm disappointed with the results as I was expecting an accuracy of around ten feet. Are my expectations reasonable for this device? Is there something that I can do to improve accuracy? TIA, Geoff

That's pretty much the setup I envisage - except that I plan to print the cache page and a Google map for each planned cache. WRT having to load LOC files individually, apparently you can merge LOC files to make a single file to import into Beeline etc. (I noted on the Groundspeak Licence Agreement that you're permitted to merge cache data for personal use, so hopefully I'm not in breach of anything by providing the following instructions.) To do this: Start a new text file and copy (and paste) the first two lines of one of your LOC files into the new file. You should then have: Paste the waypoint definition (including the opening and closing tags - i.e. everything from <waypoint> to </waypoint>) to the new file Repeat the previous step for each additional LOC file you want to combine After the last "</waypoint>" tag in the new file, type </loc> Save the new file and import it into your PDA application HTH, Geoff

My thanks to both racingmissy and Smurf. I now know that geocaching with my PDA is possible and I've got a much better idea of what's required. Thanks again, Geoff

I tried using the search facility - but the main keyword (i.e. "PDA") has fewer than five characters and so the system rejected my search... I'm new to geocaching and haven't yet got a suitable GPS. However, I have a Fujitsu Siemens Loox N520 PDA with a SiRFstar GPS antenna built in. Currently, I'm using this with satellite navigation software that doesn't permit entering lat/long co-ordinates but I suspect with the right software (e.g. Memory Map, or perhaps something a lot simpler from the freeware/shareware sector) my PDA might be usable and so I'd be grateful for comments. TIA, Geoff