I mispoke - the roelofs prism I thought i needed is currently at $285 on ebay:
A sheet of paper beats that anyday!
Half Bubble and Kent are right on.
The only thing to add is if you really want to do it I would download the pdf of the last booklet that Elgin Knowles and Senne published. It will walk you through the process.
This thread has caused me t o make a New Years Resolution. My north arrow will represent a reproducible bearing based on either grid or true north, probably grid most of the time, but labeled in such a way as to be reproducible.
I have become so used to the concept of the bearings merely representing angular relationships and not having any meaning beyond that. Except maybe a location magnetic bearing sometime in the past. I work in a heavily monumented area so lack of monuments is rarely a problem. I used to work in TN and learned solar observations from Howard in the early 80's. I don't recall Howards last name, he worked with me at Ragan Smith and Murphy and was my mentor for the difficult stuff. He was also a firearm enthusiast...Ring any bells for anyone? He worked with John Spry...
So, why make my north arrow mean more than a symbol?? To make the work easier to reproduce under any circumstances. Not that I agree with the doomsday scenario of "all monuments lost", but to make my work a little more professional.
I've been thinking about this since the post was first brought up and have to thank Kent for throwing this out there.
Don
> I've been thinking about this since the post was first brought up and have to thank Kent for throwing this out there.
I think that posterity will thank YOU for this, Don.
:good:
Thanks for the very straight-forward explanation. I now know what resection actually means - yeah! For this particular exercise I am able to set up directly over the pins/bounds but do not have line of sight to any other markers due to the area being heavily wooded. Hence my interest in finding "North" - which as you point out could actually be any known reference, but I mistakenly thought there was a really easy way to do this.
And no, I don't even rely on GPS to get home, much less locate monuments. I'm acutely aware LLS is Licensed - hence the "L" in LLS. Indeed here in NH there is currently a committee of surveyors looking at the longstanding issue of septic designers often being in the position of technically doing surveying work - something we are not licensed to do. The NH DES has always turned a blind eye to this, but some surveyors are now squawking because business is slow. However, the actual language of the RSA appears to allow some latitude (no pun) with regard to what I term "incidental" survey type work. But I'm not willing to test my legal theory in court just yet.
So, as yourself, I am a keen amateur who knows the "bounds" of my area of expertise and am very careful to get the proper stamps from the proper people when required. I am quite risk averse that way.
Thanks again!
My north arrow will represent a reproducible bearing based on either grid or true north, probably grid most of the time, but labeled in such a way as to be reproducible.
Most of the more recent "true north" surveys that I see (including some of my own) are really gird bearings with the central meridian of the grid along the longitude of wherever the solar (or GPS control) was observed to begin the survey. From there grid angles were turned. I know it really doesn't mean much in a lot survey, but as the survey area expands the error from true north does also.
You can say the survey is grid: grid north=true north at lat. long., or at the southwest corner of the Jones Subdivision; some defined point. That should allow the next surveyor to easily plug right into the bearing system.
Of course, you can actually survey in true north with each bearing corrected, but it's kind of a pain and doesn't merge very well with autocad.;-)
I agree with you in what you said, MightyMoe, except that I personally don't care much for the term "True North". I use the term Geodetic North - some places might require consideration of the LaPlace correction to their Astronomic Azimuth to make the statement legitimate. In East Texas, they are practically the same. If one isn't comfortable messing with that, I'd lean more toward the technically correct "Astronomic North" over "True North". True North is just a little too ambiguous and not really technically correct for my taste.
Having said that, I'd still rather see a plat, report or description with "True North" than "Record North" or "Magnetic North" though.
I don't believe that the size of my projects would influence the bearing variations between true and grid if I established true on one line...Largest project I've had in ten years was 100 acres (+/-) and most are less than one acre....most as in 90%, and the rest are maybe up to three acres....
Got it. Thanks a bunch. Looks like a lot of good stuff.
yes, kent, you need to check out the iers bulletins a and b. they are similar to waiting for precise ephemeris in post processed gnss data
INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE
Yes, I agree.
The proper description would be geodetic north (GPS) or astronomic (solar).
We just like to say true north in the PlSS.;-)
>
> First I don't know if the Lat/Long coordinates my smartphone gives are accurate enough. (I am at about 43.21.34N/72.03.53W according to whatever chip/algoritm is inside my HTC phone.) What is accurate enough for a 1 minute observation accuracy? How is this usually done? My understanding is that Lat has to be accurate to 10 seconds of angle. Is that the case for real? How is this achievable? Doesn't seem that using a USGS map can get you there, as is suggested in the literature I've read.
>
>
> The time element seems critical. How does one sync Universal Time to do this? I mean a stopwatch is suggested, but reaction time is on the order of 30-100 milli-seconds for the average person. That seems like a lot of slop to me. I know CO and HI have atomic clock signals broadcast over the radio, but I don't have a radio that receives those bands, and even if I did there's propagation delays in the radio waves - they are not at the speed of light contrary to what anyone says. So is there a special procedure for doing this or what?
>
the stopwatch trigger latency/lag time is only important in a relative sense. test it yourself. a stopwatch measurement that is absolute, say 0.01+-seconds time vs an absolute lag time of, say 1/2 second,but the relative is still +-0.01 seconds reduces to just noise. trust me on this, not really important
a handheld gnss receiver will give you a good enough location for observations, as will an interpolated/scaled location from a usgs quad map. others have mentioned this already
I'm with you.
I started to have a problem when one survey turned into two and three and four in the same area. I was shifting farther east and west and was drifting farther from north. I either needed to change bearings for each survey or express the bearing more correctly.
I'll stick to grid with a date and datum...
"I'm actually quite surprised by the accuracy that is had using these techniques."
We were even better with a stick and a string before technology came along.
"They honestly seem so convoluted, tedious, and error prone."
Well, they are. It takes a lot of slippery clockwork to do better than the stick and the string. Observation standard deviation divided by the square root of number of observations, is how good the final mean can be. Knowing that, you can apply the specs of your measuring devices to the provable accuracy you want to achieve and solve for the # of redundant observations (sets) & thus the procedural time required & decide if you need a better instrument or a better method.
"yep - having an RLS in the field is SUCH a PITA, all that knowledge and book-learnin
slowing the crew down 😉
so I wonder who signs+seals the survey?"
Wow! You had to work with him too !?
Wonder when we get to the chapter on sanitary inverts 😀
> Thanks so much again, even to those who took a little bruising by my little rant. I really wasn't looking to stir the pot, I was just responding the "Joe Homeowner" dig without exercising my usual restraint.
If that was unrestrained, I think you'll do just fine. 🙂
Dontcha just hate those guys that spent their days, day-in and day-out traversing through the swamp and woods and then unlearnin' all that experience at night trying to study them-there books? It makes ya wonder just who's carrying who?
I call (303) 499-7111 to get the broadcast of wwv and utilize the double-ticks for adjusting to solar time. The atomic clock is in Ft Collins, CO, but the number is in Boulder. I had that memorized many years ago and never forgot (but I did double-check and call it before posting to make sure I wasn't giving out a wrong number) In my opinion, my reaction time to the clock is compensated out when I mark the time in the field. I don't know anything about the milliseconds delay of the broadcast, but my experience has shown me that with good care on my part, I have obtained relatively accurate bearings on lines.
I like the "local-hour-angle" method, and have used it projecting the sun onto my field book. I use the ephemeris's 'apparent' semi-diameter of the sun and shoot the trailing edge. It is easier to lead the trailing edge of the sun with the crosshair and mark the time when the sun catches up to the crosshair. I always did solar shots when the time was right while I was out in the field. It is easier than "scheduling" a solar, and trying to outguess when it was going to be clear and sunny. Doing "the best you can" with the time and angular precision should give you plenty accurate enough of a bearing for your intended purposes. Getting the "technique" down is what takes the time and practice. It would be especially good to learn on a line that you already have a bearing check on, to make sure you're doing everything right.
I don't know about "total station" electronic distance meters these days, but I have always avoided pointing them directly at the sun. (I don't know if you still need to do that). I used a solar filter on the scope end (whatever it's called, not on the eye-piece end) so that I didn't have to worry about burning out the edm. If you got a roeloffs (spelling?) prism, you need to make sure it will fit on the instrument you are working with. projecting it on paper is more "challenging"/fun getting yourself coordinated with the stop watch and such. If you aren't collecting the data electronically, it's nice to have someone there keeping notes.
As to your earlier argument/rant; you might remember we often work with or for people who don't understand or care about our bearings or anything else. they just want our bills lowered, and many consider a survey a necessary evil. Also note that solar observations are kind of an old-school practice and many surveyors today have never done one.