ArtMan Posted April 1, 2006 Share Posted April 1, 2006 This one is new to me. We're all familiar with true bench marks (vertical control points), where the horizontal position is estimated from a topo map. Planning for a possible expedition this weekend, I pulled up the data sheet for station EASTON (HV0046), in Easton, MD. There are a couple of interesting things here. First, the station designation has changed. The previous designation, "EASTON BM 1935," can be seen on the ca. 2000 datasheet archived on the geocaching site. This kind of change/simplification is unusual, but I have seen it a couple of times before. What I have never seen before is this: The earlier datasheet has the familiar language, "The horizontal coordinates were scaled from a topographic map and have an estimated accuracy of +/- 6 seconds," and the latitude and longitude are given to whole seconds only. The current datasheet has the coordinates in tenths of a second and the following language: "The horizontal coordinates were established by autonomous hand held GPS observations and have an estimated accuracy of +/- 10 meters." The newer datasheet has three recovery reports that do not appear on the older sheet: Maryland Highway Adminstration (2000) and U.S. Power Squadrons (2002, 2005). I have reported handheld, consumer grade GPS positions numerous times, but it always ends up as part of the text in the recovery report. How is it that this handheld GPS report made it to the top of the datasheet? Curious, -ArtMan- Quote Link to comment
Z15 Posted April 1, 2006 Share Posted April 1, 2006 (edited) The online recovery entry form start page does not appear to be updated to allow this entry BUT I (have no data to enter) don't know if there are subsequent screens to enter the GPS positon. This has been in the planning stages for several years, that is, allowing the updating of position with GPS and adding images to tthe datasheet. Edited April 1, 2006 by Z15 Quote Link to comment
DaveD Posted April 1, 2006 Share Posted April 1, 2006 NGS is testing the process of adding hand-held coordinates to update the scaled positions of BMs. This process, which currently is limited to several state DOT's and the NGS state geodetic advisors will become part of the on-line recovery program. Quote Link to comment
ArtMan Posted April 2, 2006 Author Share Posted April 2, 2006 NGS is testing the process of adding hand-held coordinates to update the scaled positions of BMs. This process, which currently is limited to several state DOT's and the NGS state geodetic advisors will become part of the on-line recovery program. Thanks, Dave. I had a feeling it might be a pilot program of some sort. I don't know how much intelligence is built into the web-based reporting system, but I wonder if you have considered some sort of error-checking routine. For example, since the scaled coordinates are nominally accurate +/- 6 seconds, perhaps if a user enters coordinates more than 6 seconds — or maybe less, since in my experience the scalled coordinates are usually much better than that — might invoke a subroutine to ask "are you sure?" or possibly kick it out for manual review. Just a thought. -Art- Quote Link to comment
+Black Dog Trackers Posted April 3, 2006 Share Posted April 3, 2006 The estimated accuracy of +/- 10 meters seems rather large. Is that at a 99 and 44/100 % confidence interval? Here is the NGS reference (see Page 7) from a long-ago topic related to this. I'd say our GPS units are really somewhere between HH1 and HH2, but then it all depends on which confidence interval perspective you're using. Quote Link to comment
DaveD Posted April 3, 2006 Share Posted April 3, 2006 Artman - NGS does have a checking routine. Whenever we add something new to the data base we run a program called CLUSTER which provides for a variable radius from which we can compare new data with existing stations in NSRS. Typically, for most geodetic applications it is set at 100 m, for updating scaled BM values we expand the radius to 6 arc seconds. If the hand-held position being added doesn't fall within the 6 second range we reject the value until we can confirm with the submitter that they had the correct monument and are providing the correct position. BlackDog is concerned that the value of +/- 10 m seems a little high. Our studies have shown that an unaugmented GPS position (no WAAS or any other type of corrector applied) is about 10 m at the 95% confidence level, which we call HH2. Hand-held 1 (HH1) is for any type of corrected GPS which could easily be a surveyor with cm level RTK or someone with a WAAS corrected hand-held. Since we are unable to obtain independent validations of the positions being provided we have chosen to keep our estimations on the pessimistic side. Quote Link to comment
+Black Dog Trackers Posted April 4, 2006 Share Posted April 4, 2006 DaveD - So, in our NGS recovery logs, should we begin specifying HH1 if we're using a non-WAAS GPSr, and HH2 if we're using a WAAS-enabled GPSr? (I realize that we're not yet able to use the new recovery page.) Quote Link to comment
DaveD Posted April 5, 2006 Share Posted April 5, 2006 It's the other way around, HH1 if your using WAAS-enabled GPSra and HH2 if it's non-WAAS GPSr. Quote Link to comment
+Black Dog Trackers Posted April 5, 2006 Share Posted April 5, 2006 Hmm, that's difficult to remember; HH1 is .SS and HH2 is .S . Fortunately, I haven't yet used the HH code. HHSS and HHS would be easier to remember. Even easier is to have no HH code at all - whether the .S or the .SS format is used pretty much says it. Quote Link to comment
+GEO*Trailblazer 1 Posted April 5, 2006 Share Posted April 5, 2006 Excellent. HH1 for me. Should we also state the conditions of observations? Such as Heavy,light,no,tree cover. Hills or valley.,etc. I know that one part of that is self explanitory when you add the satt observavation button. But this is for those that we are unsure of. Just an observation. Quote Link to comment
Z15 Posted April 5, 2006 Share Posted April 5, 2006 (edited) Whats to stop someone from giving HH2 data as HH1 data. Are they going to have to give the make and model of the handheld to determine if they have the capability to get those reading? Fors instace, actually getting HH2 data and passing it off as HH1, either from lack of experience or on purpose. I am sure you thought of this? Are you limiting all recreational hunters to only HH2 position updating? That woudl seem appropriate, leaving the DGPS positions to approved agencies like DOT's and other survey org's. Edited April 5, 2006 by Z15 Quote Link to comment
+Black Dog Trackers Posted April 5, 2006 Share Posted April 5, 2006 I don't have WAAS on my old GPS receiver. However, I haven't heard of anyone with a hand held GPS receiver that did have both WAAS and 2 decimal points in the seconds display (.SS). Quote Link to comment
DaveD Posted April 5, 2006 Share Posted April 5, 2006 Z15, the addition of these data is on the honor system and hopefully people will have some knowledge of what they had. The bottom line is that either an HHI or HH2 value is typically way better than an scaled position to help the next person locate the mark. These data are used for recovery purposes only so we're not too concerned about any real issues with this topic. Quote Link to comment
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