Bill93
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Posts posted by Bill93
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If anyone reading this has professional grade GPS (L1/L2 carrier capability), even antiques like my Trimble 4000sse, you will have longer to make submissions that will help NGS make an accurate transformation tool for converting old elevations to the 2022 datum when it comes out. The deadline was going to be the end of 2021, but the whole program has slipped schedule.
https://content.govdelivery.com/accounts/USNOAANOS/bulletins/2fce65b
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I found this on Jerry's site, but it is a minimal article.
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I was at the Ames Brothers monument wikipedia (intersection station) a couple years ago, but was busy touristing and didn't check for benchmarks. Darn.
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I've seen hundreds of bench marks and only one chiseled square. Apparently there wasn't much leveling done in my home area other than on disks and occasional items in concrete. That one was PX0154 in downtown Cody, WY on a building foundation or wall. And it looks like I failed to report it after our trip.
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What did you think was odd about its location? The USGS pdf says it is on a bridge, a very common location.
The map in the pdf shows the routes used by the leveling crew that made the measurements. They often used roads and railroad routes, so the lines could represent either, or even cross-country routes sometimes. The lists on the following pages list the points measured, so you can trace out the route from that.
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Note on page 9 the mark 15 JWM 1950 has the notation "Tied by NGS 1950" which most of the ones in this pdf do not have. It is typical that few were so tied.
That notation is a bit strange because the agency was still C & GS in 1950, so someone added the note much later..
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It's a US Geological Survey mark. Only some small fraction of those were measured to the standards of the US Coast and Geodetic Survey and submitted to that agency, now called National Geodetic Survey.
The list on Geocaching is a 20-year old snapshot of the NGS data base. So it isn't surprising when a USGS mark is not in the list here.
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I just now checked with my Android phone and find the benchmark count on the profile/geocache page just like usual.
I never paid much attention to the statistics page so wouldn't know if it changed.
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The uptick in COVID cases is giving us doubts about travel, hotels, and indoor meetings with people from all over.
We're vaccinated but worry that may not the stop the next variant that a huge number of cases makes more likely to emerge. Darn.
Edit: I see they've moved the registration deadline to Sept 5, so we h ave another week and a half to see how the trend goes.
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Typically only a modest fraction of attendees have costumes, but they add to the flavor of the event. Sadly, Chas, who could be depended on for an authentic-looking costume as well as being an active contributor to the programs, passed away.
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If you can make it to Toledo, Ohio, Sept 22-25, and can afford the $$, this looks like another good one from the Surveyors Historical Society.
http://www.surveyorshistoricalsociety.com/Rendez.php
Thursday talks. The Friday program has lots of field activities. Saturday optional tour.
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NGS won't give anybody permission to keep a disk, but nobody will come after someone for keeping a disk that is destroyed by the building being torn down or other non-vandalism reasons. It happens all the time.
It would be great if a local surveyor could do a RESET to preserve an elevation reference. NGS has no funding to do such work.
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I don't know how many garage sale trowels I've ruined while digging down to a bench mark or other monument because they won't stand much prying force. I recently saw one of these, a gardener's Nisaku NJP650 weeding and digging knife.
Somewhat pricey at $20-25, but very sturdy, sharp edges for cutting roots or other vegetation, and inch and cm scales as a bonus. Much handier than a machete for those occasions when you don't need the length. It comes with a sheath but probably isn't legal to carry in public. A downside is that it is sharp enough to cut utility lines that the old trowels wouldn't.
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I would think a reference mark would be within easy taping distance of the station mark, and a gaging station would be adjacent to a stream or body of water.
Could there be a typo in the coordinates?
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Don't confuse USGS (US Geological Survey) who made the maps versus the NGS (National Geodetic Survey, formerly called US Coast and Geodetic Survey).
NGS maintains the master control network of lat/lon and elevation references. USGS worked off of those and set many additional disks or other marks as needed for mapping and water monitoring.
If NGS happened to find a USGS point convenient they may have measured it to their standards and added it to their data base, but that is a minority of USGS marks.
USGS never computerized their data sheets, and most are only available from filing cabinets.
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I did this once some years ago. See the first log for MH0134.
The ties hadn't checked out, which I later blamed on changes to the RR, grading of the adjacent lot, and widening of the street. The mark was beside a RR signal building and I thought it likely construction would have disturbed it.
On a hot Sunday I did a 1-way run with my wife holding the rod. I wasn't up to closing the loop in the heat. Calculations showed it checked better than I had reason to hope, so reported GOOD.
Sadly, in 2018 i went back to it to do a GPSonBM session and found fresh tracks where equipment had hit the post, breaking it and possibly driving the base deeper. DESTROYED.
That session would have filled a big gap in the GPSonBM coverage, and every other mark in the neighborhood has poor sky and/or would risk trouble with the RR.
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The only time a mark is worse than disturbed is when somebody puts it back "about where it was" so it doesn't look disturbed when a surveyor tries to use it.
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The ones I referred to are disk on rod set in a clay tile. There is no sleeve on the rod. The tile is partially filled with gravel to attempt to drain water away, but I doubt that is fully effective.
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The Power Squadron had a lot of volunteers with little training, and their reports are not to be taken as authoritative. If they found something that looked like it could be the bench mark they usually reported GOOD. A report of NOT FOUND could sometimes mean little effort was put in to looking for it. And rarely do their reports add or update the to-reach description. So their reports are helpful but not great.
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I'd say POOR with the description of what you saw. A side view photo would be a good addition.
Has the location settled with the rod remaining at its original height? Is the cover surrounded by dirt or set in concrete?
I have seen a lot of USGS rods (short ones, I think) sticking above the surroundings in Iowa. A rod with no protective sleeve can get lifted by freeze-thaw cycles. But your area doesn't get deep frost, does it?
Is the rod bent or the ball scored by a pry bar? Did someone put something other than the original steel ball on the rod?
Just trying to consider all possibilities.
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NGS has occasionally updated the wish list, but I wouldn't have a lot of confidence they would in response to a few missing in an area.
Very few on their list are going to get sessions submitted by volunteers with the equipment. NGS has to work with whatever they get that is useful. If someone does submit sessions on suitable replacements I think they will use them even though those weren't on this list. The replacements may not be as optimally located, which is why they weren't chosen for the list.
In the earlier round . I looked on Google Earth for every disk location along a former RR line for 50 miles for ones without tree cover, went out and found only three existing stable and with suitable sky to submit, and those weren't all on the list but they used them.
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There are many marks on their list that just need a recovery report so someone with the equipment might have more incentive to submit sessions on them.
The GPS requirement is L1+L2 (non-squaring process), which is beyond recreational and mapping receivers. It takes a professional grade receiver with an antenna model having NGS calibration data, centered and height measured to mm precision, with minimum of 4-hour session. The data is processed through OPUS.
In 2018 I submitted 27 sessions using an antique but sufficiently capable Trimble 4000sse receiver. There was a lot to learn and lots of hours put in, but an interesting project. Maybe again next spring.
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Each country may have a few across the border, but it seems their data bases don't overlap. Even though the BM at Father Point is the reference for all of our NAVD88 elevations and has an NGS PID, you can't get an NGS data sheet for it.
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GPS on Benchmarks deadline extended
in Benchmarking
Posted
NGS is working on an update to the vertical datum. Just as NGVD29 was replaced by NAVD88 and NAD27 replaced by NAD83 when much better data became available, now there will be new horizontal and vertical datums labeled NAPGD2022, but unfortunately delayed somewhat beyond that year by funding and COVID. When the new vertical datum is released, elevations will change by some amount from the NAVD88 datum values. It has been found that NAVD has about a meter of tilt across the country. Three feet in 3000 miles isn't too bad, but they can now do better. Most importantly, as we know bench marks tend to go away and you are lucky if 1/4 of them are left in your area. The 2022 vertical values will be defined as what is measured by GPS (GNSS?) plus a geoid value, so that projects are no longer dependent on having a physical mark nearby.
We have seen a series of geoid updates to better model the gravity, but those "hybrid" geoids still hold the old NAVD88 elevations on the marks in the data base, and only provide more accurate interpolation between those points. The 2022 datum will change all elevations to be more self-consistent across the country, using the best new geoid model they can make without depending just on old leveled benchmark values. For this they have been working on the GRAV-D project to get aerial measurement of gravity across the country and some gravity measurements on the ground.
NGS needs a tool to allow people to convert NAVD88 elevations they have to good estimates of 2022 elevations. To check and refine the conversion model, they are using comparisons of GPS measurements versus NAVD88 values on good bench marks. Most of this data is being submitted by state DOT or DNR agencies, with some from various other sources including individual surveyors or researchers with the required equipment, submitted as OPUS Share data (see map of submissions). Look up the GPSonBM project for details.
I hope that explanation helps, and is sufficiently clear. DaveD can correct me if I misstated anything.