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Autonomous Hand Held Gps Observations


ArtMan

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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-

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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 by Z15
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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.

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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-
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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.

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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 by Z15
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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.

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