Klemmer

Hey John & Shirley: I think you got a picture of an airplane I used to fly! Good job! Larry

Yeah, some benchmark pages get really trashed. One of the worst is almost every survey mark on the Hoover dam. I think the number of logs is into 3 digits of bogus or wrong logs, for 30+ benchmarks. Of course, if you recognize some names from this forum, or look for pictures, there are good logs there (including yours truly), in amongst the... er ...chaff. I'd volunteer for the committee!

Out west here, I have often seen 3 feet as the distance. But - not always...

Several days ago, I found a good email contact point for the datum experts at the National Geospatial-Intelligence Agency (NGA) [previously NIMA, previously DMA], and asked if they had any data on the older datums in question here (Yolo Base and US Standard 1901). Earlier this evening I got the answer: No data there. It was worth a shot. I also gave them the link here, so..... Here is their page with reports on datums, WGS84, and related geodesy information (TR8350.2 and TM8358.1). There you will find pretty much anything you ever wanted to know about datums, and the conversions from every datum worldwide known to man (except the really old ones we are working with in this thread). Klemmer

Mark Duster: Thanks for the idea on BLM-GLO. I should have thought of them! Will dig into it over there. I have the field notes from the 1899 survey (link in my original post above). They went to great lengths in 1898 or so to find field notes from von Schmidt's survey in 1873, but never did find them. Klemmer

Wow, Holograph, you sure got into it! So, if you ignore the problematic MY3374, then your least squares method is consistent and reasonably accurate (for our purposes). Right? Great. However, if we ignore MY3374, and there is not really a problem with it, them we're kidding ourselves. Hmmm.... Well, as I said above, my test was Klemmer's method vs Papa-Bear's method. The results were nearly identical to each other (31 inches Latitude and less than one inch Longitude). My thinking is that two different methods yielding essentially the same result pretty much proves both methods. I'll test it again in the process of doing the actual conversions for my trip, and advise. I suppose I might have just gotten lucky on one test.

Comparison of two methods: 1) Klemmer's method: Determine an average correction vector based on "Dual Datum" marks in area of interest (using Vincenty formula). Four results averaged for this trial. Apply the correction to old mark coords to get current datum (WGS84) coords Result for No 135: N35° 09' 40.7957", W114° 49' 52.6149" 2) Papa-Bear-NYC's method: Determine Dist/Az vector from known "Dual Datum" mark to target mark in Old Datum/Ellipsoid Apply same vector from the "Dual Datum" mark to target mark in current Datum/Ellipsoid Result for No 135: N35° 09' 40.7702", W114° 49' 52.6141" My conclusion: The difference between the two methods (in one trial) is insignificant in terms of the precision available from HH2 (consumer handheld) GPS receivers. For one or two marks, Papa-Bear's method might be easier to setup (only one "Dual Datum" mark required). For more marks, Klemmer's method might be easier to setup (at least several "Dual Datum" marks are needed to get reliable average). As the results of the two independent methods are so close, it sure gives me confidence in the results. Now -- to go find No 135 (mid-April or so near Laughlin NV) ! Interesting stuff (for me it was). Thanks for the help, folks!

Holy Moley!

Nice trip and pics. Thanks for the report. Fun reading. Wish I was with you. Maybe one of these days.... Don't forget Laughlin in April....

southpawas: Right, thought about that. Ran the numbers, but the result of the old pre-1900 ROUND TOP to the current ROUND TOP RESET were quite different than I got using (so far) four old/new conversions in the area of interest. I don't think ROUND TOP RESET is in the same position as the original ROUND TOP. Or, something else is wrong. I would need to try to find the older datasheets, if they exist. In any case, there are plenty of dual datum stations available along the whole border. Thanks, though.

Papa-Bear: Thanks! I like your method. Appreciate the feedback. I believe it also takes out the variable of different ellipsoids, which was bothering me. I'll give it a shot, and see how it compares to my method. Should be interesting. Will report back. Since the original post, I've looked at 4 other "dual datum" stations inteh area, and the average of the correction vector is still under a meter, so that gives me a bit more Thanks goodness for "computers". I can't imagine doing the transformations we're doing by hand. In the 1900 report, they sometimes refer to "computers" also, but were referring to a person! AZcachemeister: Exactly. A hip-shot is the idea. Breathe slowly..... FX: You bet pictures will be forthcoming (with some luck)...

Here is what the 1900 Survey Report has to say about the Datum used for their coordinates:

southpawaz: Yes, that might be helpful. Thanks. I suspected that the Clark spheroid (ellipsoid) of 1866 was used, and I have that data.... Wops! I have the Clark speroid of 1858 as an option in the Vincenty formulas. Ahhh.... Now my head hurts too. My main post above corrected to use WGS84 ellipsoid instead of the previously stated GRS80. Difference insignificant. One problem is using two different ellipsoids in the same INVERSE (Vincenty formula) calculation. I'm reviewing it, but it might not be possible (at least by me)......

I suspect this is not an easy (or short) question, but here goes: 1) Background: Several years ago, 2oldfarts, fossillady & myself (Klemmer) recovered some very neat old survey marks ("benchmarks") out in the desert west of Laughlin, NV. They are drill holes from the survey of the CA-NV Oblique Boundary Line, most from 1899. We're heading out there again in April (although we may do other areas). But – I may have extra time there. I starting doing some research on those old marks, "got hooked" and I dug out the original survey report from the US C&GS Annual Report of 1900 (Appendix 3). It's 282 pages with full scanned in maps, and details of the whole survey from lake Tahoe to the Colorado River. Nice job putting them all on-line, NGS! (BTW: if you get into it, some maps ended up in later appendices – tricky!) 2) There are tables in the report of Lat/Longs of all sorts of neat marks out there, including all their own new marks, and even lots of marks ("mileposts") from earlier surveys, including the original von Schmidt survey of 1873. Some are on USGS topos & some are even still in the NGS database, but many are not. Of course, the Lat/Long are of a much earlier Datum, in this case from the Yolo Base Datum (details on report page 346, bottom note), which was before the US Standard Datum (of 1901). I want to look for some of the marks not presently in the NGS database (or in there improperly). Decent (hand-held consumer grade GPS) coordinates would be very helpful. 3) Here's the problem / question: I know neither NGS nor USGS have datum conversions that old. No luck on-line anywhere else either. I'm looking into doing my own (local) datum conversion for that area. There are several instances where the 1899 original marks are still in the NGS database, and are (of course) also in the survey field report I have. Using the Vincenty formula / spreadsheet (thanks, Aussies!) so I can work off-line and have records, I have done the INVERSE calculations for two points that are available in both datums*, specifically T 134 (FS1155) and T138 (FS1149). Vincenty assumed WGS84 ellipsoid in this case (invalid for the 1899 coordinates!). The question is, before I setup more of them, how valid is that? In other words, if the position difference between the two datums is, for example, 5 meters at true azimuth 090°, is that correction valid for other points nearby (say 25 miles)? 4) Preliminary result: Using T 134 and T 138, I calculated the distance and azimuth for each mark, between the two datums (a correction vector of roughly 14° true azimuth and 219 meters), and compared the two results. Not too bad, but not as good as I had hoped. The difference between the two correction vectors is 0.857 meters and 0° 14' 36.691" azimuth. Makes me wonder. I haven't run more comparisons yet (it's just spreadsheet data entry time). Is my methodology valid? I suppose less than 1m is decent for HH2 GPS search, but is it real?? Maybe it is really 20m? It's a big desert. Any surveyors / historians / mathematicians / casual readers out there with an opinion? *I know, plural of datum is data, but it gets too confusing in this context.

And one for the Delorme PN-40. Fully paperless now.

I've still got my old Magellan Meridian Platinum (almost the same as the gold, plus compass). There were some serious firmware issues with WAAS (long story), with some esoteric fixes. But that shouldn't be an issue down under. Main point: Are you getting good position data? If so, then like embra said, GSAK will write the file format you need to dump waypoints onto the SD card. Forget any other file format. Maps: Magellan made one for the US called "Mapsend Topo for the USA" that could create topo maps to send over to the SD. State of the art for it's day. They also made one called "Mapsend Worldwide Basemap". That just had streets (highways + some secondary), as the title said "worldwide. Worked for me in Japan and Australia (Brisbane & Sydney) several years ago. I've still got them. Sounds like you have the AU version basemap installed, so good on you, mate! Enjoy! -- Klemmer

YEP! Amusing and Educational. Great combination. I always tried for that when I was an instructor, especially training new USAF pilots. Sometimes it also became terrifying (for me!). {Note: No joke: The Air Force at one time taught that a touch of adrenaline helped the training stick. Worked for me. Not sure if this is still the "party line" in today's PC military.} Now back to survey subjects........

A Public Service, huh? Hmmm, never exactly dawned on me in those exact terms.... I wonder if I could count my benchmark hunting hours in my monthly required Public Service / Community Service hours..... Oh, wait, I'm not supposed to talk about that... But maybe......

Leave it to Texas to do it up big Seriously, many county & local government survey offices have their own databases. Some are realtime on line, some are just downloadable files, some only seem to exist on paper. That covers several different CA counties I have found. PlanetZhanna has the only List of links to local databases that I know about. Looks like Arlington is already there. So, keep in mind that although NGS is the Big Dog, there are lots of other little doggies out there. There is also some overlap. Let's not go with the dog analogy and more..... Klemmer

Hi BillWallace: Tidal Benchmarks have their own database here. Although, I have seen a few that are tidal AND otherwise of geodetic importance seem to sometimes "sneak" into the main NGS database. Of course, the geocaching benchmark database is an old copy of the main NGS database, so very few tidal benchmarks can be logged on geocaching.com Klemmer

I'm exactly with John (2oldfarts). If you've got a PN-40 (or PN-40SE), upgrade to ver 2.7, and get the latest GSAK. It works great for uploading caches / benchmarks to the GPS, Once in active memory, the 1000 waypoints & geocaches can be saved as .gpx files to the SD card (up to 32GB usable), including the cache page & as many logs as you want, or the full NGS datasheet. You now have an almost unlimited number of caches / BMs with all data on the GPSr. OK, let's see... Typical maximum file size on the SD will be less than 5MB for almost 1000 wayoints, including lots of long-ish cache / BM full data. As far as I can see, it is the ultimate in paperless geocaching / BM'ing. If my math is right, that's about 6.4 GigaCaches (GC? hmmm?) on the unit with a 32GB SD card. With full data! Wow! That's all the caches in the world, and all the benchmarks in the US, with all descriptions, and room left for plenty of maps on the SD card. Wow... can that be right? There will be a lot of files (over 1,700), and THAT might be the limit. Pretty crazy. The time to do he dowload & upload it all.... never mind..... But it could work! P.S. No need to wait for version 2.8 firmware. Just use 2.7 and GSAK.

Hi Lee: From what I've read about T9, it will contain a "SYNC" function, which sounds a lot like the Cache Register Widget. So rather than bundling CR with T9, it sounds to me like T9 will functionally include the CR capability. Just my interpretation. I know this doesn't solve your Mac interface situation. Even as a PC, I sure wish Delorme would support Mac better. I think it's shortsighted on their part. I know several cachers / BM'ers that swear by MacCaching. If you could twist their arm into supporting Delorme PN's for direct downloading (including full cache pages / datasheets), you might really have a good route. It took Clyde at GSAK (no Mac version) quite a while to support Delorme, but now that he does, it works very nicely (with PN-40SE firmware ver 2.7). Worth a shot. Hmmm.... Did Robert Lipe (Chief Babel-Head) work with Clyde on the Delorme interface (GSAK runs a lot of GPSBabel "under the hood")? Babel runs on OSX. Maybe you've got something there... Robert? -- Klemmer (PC trying to help Mac. Possible future Mac user?)

Holtie: That sure is a unique disc. Wow! F-X: I never noticed the alchemy before. Funny! Of course, visually, I'm not sure I could tell the difference between lightly weathered (SoCal dry) copper and weathered bronze (and I used to be a Chemical Engineer!). Did you see in my other pics that later someone built three concrete tall skinny "stands" for tripod feet, so a normal tripod could be used over the mark. Unfortunately, one of them has been destroyed. Also note that it was a key mark in the California Primary arc of Triangulation (1904). Interesting place. Come on by sometime, and we'll go up there! Still a nice couple mile hike now.

Here's what you might call a serious monument: It's about 2 feet across the hexagonal and about 3 feet tall. The actual mark is a bolt in the top. There are lots more pictures of it in my log on geocaching here. It's about the fifth log down. Quite a project for 1896! They must have used pack horses to haul the concrete & stuff up there. In those days, it would have been a 5+ mile trip from anywhere settled. It's a favorite hike of mine; been up there quite a few times. P.S. Notice the dragonfly above the "A" in SAN?

ruffytiger: In case you didn't realize: USDI = US Department of the Interior NPS = National Parks Service It's pretty doubtful those marks will be in the National Geodetic Survey (NGS) database, which is where the geocaching database came from. You can search by designation here: http://www.geocaching.com/mark/nearest.aspx but your example above doesn't come up. Looks like Waymarking is the way to go on these. Klemmer