> Come to think of it, the time displayed on a GPS receiver may not be very accurate either.
Yeah, I'd want to actually compare handheld GPS UTC to WWV UTC with a digital stopwatch before I got too enamored of using handheld UTC for astro observations. Besides, it's fun to have a portable shortwave radio, particularly at night.
I get a few questions about my using WGS84 as a basis for bearings. I use WGS84 because every GPS unit collects and most are converting that to something else.
I have set control from many directions and using different control points and on different days and found the bearing to be no more than a tenth of a second difference between the same hubs every time.
For those that take astro azimuth shots, I have found this to be a handy little CLOCK.
It even displays the temperature.
😉
> In a nearby county, we have a surveyor who has used astronomic observations for years. He has recently been using GPS and comparing earlier bearings with static GPS derived bearings. He is finding that after applying adjustments from grid to astronomic he is hitting within seconds of his previous work.
>
> That really tickles his fancy and shows just how well surveys could have been placed on a repeatable bearing basis for decades.
Yes, that's been my experience also. I used a one-second theodolite for solar azimuth observations and got azimuths that had apparent standard errors on the order of about 1.5 seconds. I haven't found any surprises as I've gone back with GPS to the same surveys. An extreme example was a West Texas project where a traverse network was oriented from multiple solar observations by which grid bearings were derived. Going back years later I found bearing errors on the order of less than one second between stations thirteen or so miles apart. The legs were long on that traverse and it was cleverly adjusted, but the solar observations gave a very, very good answer.
> How much latency is there when someone observses (sic) the crosshairs and yells "mark!".
>
> A lot more than if the observer simply pushes the lap button on the stopwatch themselves.
The same person should synchronize the clock to the atomic clock signal as well. That person's reaction time will then be factored in to when they mark the time.
We Are At 25 Leap Secongs Since UTC Was Started
I believe that it is 14 seconds since GPS time.
There is talk of doing away with the leap seconds in GPS. I have no clue how that math will work.
Just remember 1 second error in time is a 15 second error in longitude.
A single solar observation does not mean much.
Polaris at elongation being the quickest.
Paul in PA
[sarcasm]craziest thing about this thread is that a few short years ago, you were chiding me about training people on solars.......
glad you've come around.....[/sarcasm]
hmmm....the only question that comes to my mind about that is:
Was he chiding you about teaching solars?; or
Was he chiding you about teaching solars? 😀
For the purposes I've used solar observations in the past, DUT was superfluous. My solars always agreed with GPS derived bearings to within 15 arc seconds. The time displayed on my 10+ year old Garmin Etrex was very near UTC every time I checked it against WWV. Apparently it doesn't display GPS time, but corrects to something near Coordinated Universal Time. Of course, I was just watching the seconds tick by on the display, there's error in that beyond even the DUT correction, but I'd always run a calculation on one of my sunshots with an intentional 1 second error thrown in just to see what a full second would do to the results (it's not consistent and changes based on time of day, time of year, latitude). It was always enough to be apparent, but not enough to be a problem for aligning cell towers or getting a bearing to begin a boundary survey from (ultimately to be rotated to a more precise GPS derived bearing).
Your mileage may vary, but I'd take bearings +/- an arc minute to something reproducible, ie Grid, Astro or Geo, over an ambiguous "record bearing".
I have used my 41cx in that manner also for sun shots with a program shared by a fellow poster and tweaked by myself for multiple sets (three each face) on the trailing edge. Sadly my HP is on the way out with a deteriorating screen and well used buttons, that start the time manually with my computer time.
I would be satisfied with a clock/gps/solar calculator that keeps track of time/rough location/and multiple set shot times, at each observation and split time.
It'll take enough people asking for it to become a reality, but all the technology is there for a total station to be able to spit out an azimuth in real time either by being pointed by an operator or automatically by a robot with a filtered lens. The pieces just need to be put together to make it happen.
Those fancy robots with cameras built in (Trimble, Leica and Tocpon sell them) should be able to accomplish this with a little code to do the reductions and a cheap GPS receiver (such as found in a cell phone) to get time and location. A robot could even turn the proper zenith and then pan 360 degrees to find the sun. Could probably set the instrument up and have your first azimuth in 30 seconds. Everyone would be able to relate their work to a reproducible bearing with little to no effort - and it isn't that far fetched. Just needs enough clamor for it. Besides, what's the last major update to the total station that made people want to buy a new one?
> a few short years ago, you were chiding me about training people on solars.......
Well, it is pretty crazy to be doing solar observations in Montana unless the Big Sky state has somehow closed up. In Montana, are there any surveyors who DON'T have survey-grade GPS equipment?
I'm recommending astro observations for the folks in the Little Sky states and cities where GPS may be less feasible.
We do it that way so as to preserve the monopoly.
If you go putting repeatable grid bearings on everything, next thing you know it's not just grid bearings, it's grid coordinates, and you're down the slippery slope of defining boundaries by coordinates instead of by monuments.
I'm pulling your leg pretty good, sure, but a while back, one of my mentors gave me a stern lecture about how you can fly a section breakdown into the interior with GPS but until you go dig up some other "monuments of local report" you are just imposing a grid instead of a deed and neither one is the monument or the occupation.
> When the people to whom we provide our surveying services cannot find their corner monuments because we have used GPS, True North, Grid north, etc., what is the point of having their land surveyed? Just about any land owner can use a compass to find the monuments.
I don't know about your neck of the woods, but in mine, handheld GPS has made *Joe property owner* a surveyor. In fact, they could care less about bearings; they just want the GPS coordinates so they can find their corners. I would think the generation of today knows as much about using a compass, competently, as they do about using a rotary dial on a telephone.
I am convinced that Kent's original post was directed solely at surveyors, not land owners. After all, the land owners more than likely won't be retracing the lines and corners that define their boundaries. Hopefully that will be a task left in our charge.
> I don't know about your neck of the woods, but in mine, handheld GPS has made *Joe property owner* a surveyor.
Yeah, and aren't GPS-enabled smartphones even carrying things further? If there isn't a "Find Your Corners" app now, check back next week.
> I don't know about your neck of the woods, but in mine, handheld GPS has made *Joe property owner* a surveyor. In fact, they could care less about bearings; they just want the GPS coordinates so they can find their corners. I would think the generation of today knows as much about using a compass, competently, as they do about using a rotary dial on a telephone.
>
> I am convinced that Kent's original post was directed solely at surveyors, not land owners. After all, the land owners more than likely won't be retracing the lines and corners that define their boundaries. Hopefully that will be a task left in our charge.
and @ Paul who stated:
...the stars are not clear every night, the skyview is not clear every where and survey budgets are not unlimited.
Paul in PA
______________
I am "Joe Homeowner*. I learned how to use a compass when I was a kid orienteering with my folks. Goecahing with GPS is just a modern upgrade. I make it my business to keep so-called "professionals" in check. I do indeed retrace survey lines. I very rarely rely on a compass in the "Granite State" where I reside as many monuments are "carriage bolt in large boulder" - which is to say MASSIVE granite boulder. I live in a rural area and the 6 or so surveyors I work with regularly are top notch. But even so, like attorneys, they are human. Humans make mistakes; they get tired; they get sloppy, they get in a rush; they have "a budget". It has been my experience that because of these factors, they cut corners; they make mistakes; they think nobody will notice. I notice. I am a homeowner. You'd be surprised how many homeowners care about where their boundaries are and actually do "walk the lines" looking for the monuments that the "professionals" should have installed, but were too lazy, sloppy, or rushed for time not to install. Then there are those nifty remnant pins still in the ground but not on any know plan that the uneducated homeowner points to and claims "that's the boundary right there boy!". Then there are neighbors (like one of mine) who call the cops claiming I'm moving boundary markers, (which are only temporary benchmarks) *I* placed there in the first place. I've been in court over easement rights where deed descriptions are scrutinized for the many inconsistencies they have (Did I mention attorneys are human too and not immune from complacency, error making, etc.?) We also scrutinize survey plats with the attendant errors and inconsistencies. We get rulings based on all this by the court's best surveyor - the judge. Can you say IRONY?
I have my own illusions to get through life, but trusting "professionals" is not one of them. Ironically I'm a professional also: I'm an engineer, a realtor, a septic designer, a homebuilder, a land developer and now an amateur land surveyor. I like this field and I really like this forum and the folks who take the time to post and especially those who take the time to post thoughtfully. Right now my biggest problem is figuring out how to get the POS GeodimeterCU to talk to my POS windoze7 running the POS Civil3D drafting software. But that's for another thread.
What I'd like/need is a clear explanation, or a "bearing" so to speak - to an explanation on how to find magnetic or true North - without having to buy a $500 sun filter for my theodolite. The Polaris method sounds good, but I don't get the bit about time syncing to a shortwave radio. I have a smartphone. I'd like to use it to get at least minute of angle accuracy if that is even possible.
I agree with another post in this thread that for $20K my Trimble total(ly useless) station should have this feature built in - but it doesn't. Turns out this Northing business matters to me. I look at all the survey plans I have - all done by "professionals" - and the worse one simply has a North arrow pointing to the top of the page. Super if you want to find the top on the page. The best has a note stating "all bearing shown are referenced to a magnetic meridian observed on October 17, 1997. Wow! So how the heck do I correlate that to the topo survey I just did 5 days ago for the house and driveway I need to stake out? I have a smartphone, a stopwatch, a computer, a 1-second of angle theodolite and a 5 second of angle total POS- err station.
How about you, Kent? Do you have a good reference to point me to (pun intended) re finding "North"?
> Come to think of it, the time displayed on a GPS receiver may not be very accurate either.
correct, dave. lag time from gps time to utc is in the neighborhood of 18 seconds. caveat emptor
Mr. Land Ho
You are interesting.
For starters, you apparently have invested in survey equipment.
And, you want to recoup that investment.
And you are a developer/Realtor/Landowner/Investor.
And, you want information, of the sort that indicates you don't really know how to USE that equipment.
You are walking a fine line. Usually, either the REALTOR wins, or the SURVEYOR, but not both!
There are actually a few Realtor/Surveyors here. But, that is not the usual.
As a surveyor, there is more to this business, than meets the eye. It's just not a situation where all the products that are sold as a survey, are truly a survey. Some are not.
Keep learning.......
Nate
LandHo, You Misquoted Me
Correction, Paul in PA stated:
"The Sun Don't Shine Every Day...the stars are not clear every night, the skyview is not clear every where and survey budgets are not unlimited."
Your best bang for the buck is plotting an orthorectified aerial photo, from Google Earth if you can plot the satellite image or better yet a local GIS.
Because septics sometimes have to be squeezed in to within 10' of the property line you best have an arrangement with a local surveyor. Consider what it would cost to relocate a $20,000 system and pay the adjoiner damages to boot. Plus the adjoiner's surveyor could turn you into the board for going beyond your level of expertise.
Paul in PA, PE, PLS
Mr. Land Ho
Good one :good:
Find three trees with moss growing on one side of the stump (this will be north in the granite state), locate with GPS (preferably consumer grade handheld), perform least squares adjustment (freeware, don't worry about what it does), go with it.
No monuments? Seller looking for lowest price survey to satisfy the purchase agreement is certainly not going to pay for that.
Don't complain about poor business decisions you made based on not understanding the business or market you deal with.
Kent is amazing, but you want to know something about a parcel for a particular use, then you must include it in the contract and pay for it.
Just a contrary opinion, no disrespect intended.