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Everything posted by Bill93

  1. Bill93


    The web site says: "Receiver Type: GNSS single frequency with carrier phase tracking" OPUS requires L1/L2 dual frequency reception. Some other post-processing software will take L1 only with phase tracking data. I'm not sure if this unit can provide the individual satellite raw data needed for this, as I'm not familiar with the interface formats the product sheet mentions.
  2. Yeah, it's complicated, and I have only limited knowledge. NAD83 doesn't really have an x axis, or if it does it isn't important, because NAD83 is tied to the North American tectonic plate and not to the rest of the earth. WGS is fitted to the whole earth, and is a snapshot (updated every so many years) of the fit determined by international scientific groups. Its x axis is 0 degree longitude, and that is about 100 meters from the old Greenwich astronomical observatory meridian. There are discussions out on the web about why it doesn't match, which I vaguely recall had to do with deflection of the vertical due to gravity variation versus location, and continuity of time scales. The 2022 datum will be more like IGS and WGS, and there are documents and seminar recordings on the NGS site explaining it. I hope something in this ramble helps sort out the stuff you read, and that Dave D comes along to correct my mistakes.
  3. I found this on Jerry's site, but it is a minimal article. http://www.penryfamily.com/surveying/statesurvey.html
  4. 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. https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=MO0477
  5. 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.
  6. 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.
  7. 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..
  8. 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.
  9. 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.
  10. Nice to see you posting - I hadn't noticed you on here for a looooong time. Also good to see someone working with the technical side.
  11. I did some extensive averaging experiments with my Garmin a decade ago, and found that there were computational errors (roundoff of intermediate values?) that limited the resolution to a foot or two. Averaging might still reduce the error below that. I was getting differences of several feet from day to day on 2-hour averages, and did a lot of days, but never felt I was getting to the foot level. Professional grade receivers get their accuracy by using carrier phase rather than the code timing that most handhelds use, receiving multiple signals from the satellites (GPS L1 and L2, for instance), sometimes receiving multiple constellations (GPS, GLONASS, GALILEO, BEIDOU), correcting for iono/tropo delays by comparison to known stations which are relatively nearby that received signals from the same satellites at the same time, and using time averages. The known stations are either a) fixed CORS stations or proprietary network stations run by Trimble, Leica, etc. This processing is done by NGS program OPUS or vendor proprietary software. The fixed stations are typically a few 10's of km away and multiple station comparisons are made. Or b) processed using proprietary software against a local base receiver whose coordinates are taken as known. The relative position vector is quite good if the distance between is less than a few km. OPUS and some of the proprietary processing methods are known as Static, because you leave the receiver in place for a while. Some of the processing methods are known as RTK (real-time kinetic) because a radio link brings the fixed-station data to the receiver for immediate processing. There is no way you will ever get good enough results with amateur equipment to get a mark into the NGS data base. Their procedure is called "Bluebooking" after the original manual for the process. It requires extensive measurements (multiple 4-hour sessions?) with professional grade L1/L2 equipment and a lot of arcane file submissions. They expect to be repeatable within a cm or two.
  12. 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.
  13. In my hometown a stone post was placed in the cemetery, a place without wire fences or water pipes to distort the magnetic field. Later, steel coffins became much more common, so that might not be such a pristine magnetic environment. True bearings were given to the courthouse peak and a church spire, both of which are now gone so we can't use the bearings. The stone post is cracked but still there level with the ground as of a couple years ago. I did an OPUS share on it just to perpetuate the history. https://geodesy.noaa.gov/OPUS/getDatasheet.jsp?PID=BBFS77&style=modern
  14. 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.
  15. 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.
  16. Bill93


    That means the mark had an NGVD29 elevation, but it wasn't considered good enough data to be put into the NAVD88 adjustment. Look at the SUPERSEDED data down lower on the data sheet for the NGVD29 value. VERTCON applies an interpolated difference between the two datums to arrive at a usable, but not super precise elevation in the newer NAVD88 datum. There are some stations that have classical observation data for both horizontal and vertical, but it isn't common because of the way sites were selected. Triangulation stations were usually on high points whereas elevation marks were along railroads or roads where possible to take advantage of easy terrain. When GPS is used, those tri stations may end up with 3-dimensional coordinates.
  17. 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.
  18. 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. https://www.target.com/p/-/A-79542798
  19. 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?
  20. 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.
  21. 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.
  22. 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.
  23. 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.
  24. 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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