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holograph

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Everything posted by holograph

  1. The parts cost that. I also used some parts on hand, so I guess if you had to buy everything it would be maybe $325 in parts, each, excluding the antennas. You can buy similar assembled and ready-to-go receivers for $400-$500 (each) from Sparkfun, without antennas. The uBlox F9P module is a dual frequency L1/L2 receiver that can be configured as either an RTK base or rover. As a base, it can generate RTCM 3 messages, and as a rover it can read those messages and compute a RTK solution. I wrote my own communications software interface using an ESP32 module (about $8) that doubled as a memory card data logger, captured the raw pseudo-range data, and then I post-processed it. My UI is still a rough prototype and I haven't been motivated enough to put together a user-friendly RTK system. Basically, my base station is battery powered and connects to my home WiFi network. My rover is also battery powered and connects to my cell phone using Bluetooth. The batteries are off-the shelf 5v phone-chargers that can power the receivers for 24 hours or more. I've attached images of the base station unit and the rover unit. They're not as compact as commercial versions, but they were fun to build.
  2. I did an experiment with a couple of (relatively) inexpensive RTK receivers (uBlox F9P) and the RTKLIB software, to locate a point in my back yard to a precision of about 2 cm. Fortunately, there is a NGS horizontal control about 1.5 km from my home, and I put one receiver over my mark in the back yard, and the other over the NGS mark and let it gather data for about a half hour. Then I put the data in to the RTKLIB post-processing software and got a position for my mark. I repeated the process several times over several weeks, and kept getting the same results within about 1 cm. My goal was to be able to set up a base station in my back yard that doesn't risk getting stolen, and use the rover around my neighborhood for accurate mapping data. Each receiver cost about $250 dollars, and I built them myself from parts. It was largely a project to entertain myself. I think you can buy a turnkey receiver for about $400-$500 dollars.
  3. Hello, friends. I let the holoscenes.com web site expire last fall, but still retain the domain names. It's been nearly 6 years since I moved to Maryland, and haven't attempted to update the statistics since. It became quite hard to download the activity from the NGS site, and now it looks nearly impossible to capture the recovery statistics and rankings for individuals on Geocaching.com, due to site changes over the years. For old times sake, these were the last two maps:
  4. #1 - given the measurements from the centerlines, I would guess it is on top of the lava flow. #2 - Probably destroyed. It was across the street from house #3031, between the road and what was a wire fence at the time. I'm guessing that house #3044 was built since the mark was set, and its driveway was put directly on top of the mark. The "extended centerline of the driveway" would have been the centerline of house #3031. It looks like the driveway for #3044 was cut through part of the outcrop.
  5. You know, I hadn't thought about that until you mentioned it. I normally think of the Mason-Dixon line as being the MD-PA border, but if I recall, they also surveyed the tangent line between MD and DE. I'll have to look it up once my books are unpacked. Are there boundary stones for the MD-DE lines?
  6. Thanks for all the good wishes. Yes, when I moved to NJ 9 years ago, I used benchmark hunting as an excuse reason to venture out into the countryside and familiarize myself with the nearby area. Once time allows, I hope to do the same again in MD.
  7. For those of you who have wondered about the lack of updates to the statistics and maps, here is the status. Superstorm Sandy disrupted the November update by knocking out power for 7 days at the beginning of the month. After that, I got involved in buying a new home, which eliminated my spare time for the December update. This month I am actually packing and getting ready to move from New Jersey to the Maryland Eastern Shore, so I probably won't have any time for doing updates this month, either. On top of all that, the NGS web site changed just enough to make it harder to get a good snapshot of activity, and it makes the process somewhat longer. All that has combined to delay updates to the statistics and maps. I did do a download and update in mid-December, but found no new reports, so I didn't bother to do the rest of the process or update the web pages. I hope to be more or less settled by February, although even then, renovations on our new home will probably be consuming a large fraction of spare time.
  8. holograph

    Sandy

    We just got power restored to our house yesterday (Monday the 5th). It was off from Monday to Monday, a full week. There has been a large amount of damage where we are in Sussex County, NJ, but fortunately, the trees surrounding our house managed to stay (mostly) standing, with no damage to us. Nearby homes were not so lucky. There are large numbers of trees down, and many power lines still down or dangling. A number of nearby streets are still closed. A large amount of cleanup remains to be done, with no help coming from the nor'easter forecast to hit the same area tomorrow. As Harry mentioned, odd-even gas rationing is still in effect, although the long lines at gas pumps seemed to have abated. There are no generators or gas containers available in northern NJ and eastern PA.
  9. What are you hoping to calculate? As far as I know, the various heights are measured, or calculated through the models that the NGS has. I'm not sure there is any kind of reasonable do-it-yourself calculation, other than making use of the NGS models and tools. For instance, you asked "How do you find the geoid under a land mass?" I think one answer is "first, you launch some satellites, then you build a network of laser and doppler ranging stations that can precisely measure the paths of the satellites, and you then run some computer models on supercomputers to calculate the location of the geoid, taking into consideration tides and seasons." Or another kind of answer would be "you look at the datasheet to see the geoidal height" or "you use the NGS geoid model tools".
  10. A concise (perhaps too concise) summary of orthometric, dynamic, geoidal, and ellipsoidal heights is on page 75 of "Introduction to Geodesy" by James R. Smith.
  11. Over the weekend I was reading one of his reports to see if I could discover how the King triangulation was done, when there were virtually no reference points available. I was interested to read that they started at the westernmost end with a 64-mile "base line" that was measured by finding the astronomic latitudes of two peaks nearly lying north-south of each other, and computing the base line distance based on their latitudes and azimuths. Hardly a precision method! Here are a few snippets from the Geodetic Appendix to the first volume of the King report, pp 763-769: It really is amazing that they accomplished what they did.
  12. Unless you have evidence to the contrary, I doubt that the railroad used much concrete when it was first built or when the King surveyors would have been in the area. Railroads tended to be built on the following principles: do grading, and lay rails as quickly as possible, often with widely spaced, unballasted ties laid directly on the grade. The bridges tended to be timber trestles, which were later either filled with rock to form embankments, or which were later replaced with iron or steel bridges. American railroads were built fast and shoddy, in order to get revenue as quickly as possible, and were then upgraded later.
  13. Another piece of the puzzle: The CGS Special Pub 212, "Triangulation in Wyoming [NAD 1927]", has this station description. Note that it is reported by C. I. Alsakson, the "CIA" mentioned in the current NGS datasheet. That resolves the issue of whether 200 feet is a reasonable difference between datums over 100 years (it is). Pilot (U. S. G. S.) (Sweetwater County, C. I. Aslakson, 1931). -- On highest point of summit of prominent elevated table-land (with precipitous sides) known as Pilot Butte. To reach from Rock Springs go northwest 12.2 miles (1.2 miles beyond end of pavement) on U. 5. Highway 187 to point where very dim road turns left from main road just east of guard-rail, follow dim road 1.7 miles up onto table-land to point where road comes in from right, keep to left, go 3.3 miles to fork, keep to left on main road, go 4.4 miles, take right fork, go 1.4 miles to point where very dim road turns to left toward butte just after crossiug draw, turn left and drive to foot of butte. Station is easy 30-minute pack up northeast corner of butte. Marked by standard U. S. Geological Survey station disk in drill hole in rock outcrop. Reference marks are standard reference disks in drill holes in outcropping bedrock, note 12a. No. 1 is near north edge of butte, 10.925 meters (35.84 feet) from station in azimuth 208°43'. No. 2 is 7.10 meters (23.3 feet) from station in azimuth 321°47'. Following azimuths are from station : Salt Lake-Omaha Airway, site 15, beacon, 340°20'38"; Boar's Tusk. 199°46'35". Elevation: 2.417.8 meters (7,932 feet.) So Pilot Butte has appeared in 5 distinct publications: Survey Year Surveyor Position Datum ------------------------ ---- --------------- --------------------------------------- ------------------ King survey map II 1876 A. D. Wilson N 41° 38' 28 W 109° 21' 04 none (scaled from map) Hayden survey report 1877 A. D. Wilson N 41° 38' 34.00 W 109° 21' 19.60 none USGS Bulletin 440 1908 R. B. Robertson N 41° 38' 37.52 W 109° 21' 05.1 U.S. Standard 1901 CGS Sp. Pub 212 1938 C. I. Aslakson N 41° 38' 36.528 W 109° 21 04.889 NAD 27 NGS Datasheet MQ0466 1993 N 41° 38' 36.40815 W 109° 21' 07.37282 NAD 83 If we calculate the differences between the positions, here are the results, in meters. Hayden USGS 440 NAD27 NAD83 -------- -------- ------- ------- King 1876 186.9 m 294.8 m 263.9 m 270.9 m Hayden 1877 - 352.7 m 349.3 m 292.6 m USGS Bull 440 - - 31.0 m 62.8 m NAD27 - - - 57.6 m
  14. There have been multiple adjustments since then. The 1908 position would be the old US Standard datum, which was adjusted when NAD27 was introduced, and again when NAD83 was introduced. 200 feet is not out of the question, but unless we had access to the USGS data sheets for 1908, we can't be sure that the aluminum disk is a reset of the old King Survey mark, or whether MR0823 is. When you can find station descriptions from other old surveys, such as the Wheeler survey or Hayden surveys, they often used rock cairns to mark the station, especially on peaks. They weren't striving for millimeter accuracy -- Wilson noted in 1978 that he was quite pleased with an 8-inch closure error, given the equipment he had. Yeah, I really like the way they wrote up their campaigns -- there is a lot of intriguing information there, even if it is just a sentence or two. "Mr. Bechler being compelled to leave the field earlier than he would have done on account of the Indian troubles, he did not finish more than half of this section."
  15. The first description that I found was in the USGS Bulletin 440 "Results of Triangulation and Primary Traverse 1906, 1907, and 1908". "Signal and station mark: A cairn 5 feet high centered over aluminum triangulation tablet cemented in solid rock." edit: An interesting aside: apparently A.D. Wilson occupied Pilot Butte during the Clarence King survey of 1871-1872. It appears as a triangulation point on King Survey Sheet II. The King survey was one of the first surveys in the west to use triangulation. A.D. Wilson mentions revisiting the point in 1878.
  16. What are the odds of catching a scene like this in Street View at one of your marks (KV2873)?
  17. It looks like it is MD0892, in Whitley County, Indiana.
  18. LY2291, which you recovered as NOT FOUND in 2008, has been removed. edit: Just a note, the archives at this page still include LY2291 from September 2008, because my archive is updated by merging, not complete replacement. So datasheets that have been deleted recently may still be available in my archive, even though they are not available online at the NGS site. Unfortunately, as a result of the changes that made, the statistics are now obtained from the NGS archive, not my own, so the deleted stations are no longer counted. Here was your recovery report: LY2291 STATION RECOVERY (2008) LY2291 LY2291'RECOVERY NOTE BY GEOCACHING 2008 (PR) LY2291'BRIDGE HAS BEEN REBUILT. NEW DISK RESET BY NEW YORK DEPT OF LY2291'TRANSPORTATION MARKED G 449 1982 RESET 1999.
  19. The September statistics are available on the statistics page. The maps and counts by county have been updated also. There were 861 datasheets updated with new GEOCAC recovery logs. The most recent recovery added to the datasheets as of October 6 was September 17. Please note that due to changes at the NGS site, it is impossible to capture the most recent datasheets for all states. The statistics are now based on the archived datasheets. Some states may be more than a month out of date. Even if you see your recovery report in the online datasheet, the NGS archived datasheets may still be out of date (see the NGS archive). If your state's archive is dated more recently than October 6, then it was not included in these statistics. If your state's archive is dated older than the date on which you first saw your report appear online, then the NGS archive is simply out of date. Yes, it's messy. There is nothing I can do about it. In short, if you think your reports have not been counted, wait until you are sure the archive has been updated before complaining about it. Better yet, download the archive yourself and examine the datasheet to see if it contains your report.
  20. If you go to the NGS page to download datasheets by load date, you will see that it is broken. That means that the only way to obtain updated datasheets is by downloading the full archive. Each state's archive is updated on a different date. For instance, as of Oct 6, Iowa, Illinois, South Dakota, and others had last been updated September 3-8, while several New England and Western states were updated Oct 2-6. It makes it difficult to get a "fair" monthly snapshot. Some states will be more up to date than others.
  21. And lastly, the Power Squadron is no longer actively reporting marks. They used to have incentives for their members to find and report marks, but they discontinued that program a couple of years ago. I don't know exactly what the incentives were -- whether they were carrots or sticks -- but they tended to generate a lot of reports, many of which were dubious accuracy.
  22. What are some of the states and counties that have updated datasheets?
  23. That's interesting, because it implies that the retrieval by load data is not working correctly. Unfortunately, the full archives are not updated all at the same time -- it looks like about 3-6 states are updated each day, whatever can get done between about 5-7 AM, and there is no single date when all datasheets are available.
  24. There have been no new GEOCAC log files published for the last two months, so no new statistics. At some point, I plan to do a complete archive download just to check that the NGS datasheet retrieval by load date page doesn't have a bug that is preventing new recovery reports from being captured in my monthly process.
  25. The reports that you submit to the NGS go through a review process before being published. It is not unusual to take a month or more before they show up. For example, as of August 1, the most recent report that had been published was dated June 24.
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