This has to be the lowest wattage entry for 2001 thus far in the Bearing Basis Notes category, Public Records division.
"BEARING BASIS derived from true North observations using G.P.S. (Trimble 4400) R.T.K. system the 12th of December, 2001 A.D."
Love the addition of the "A.D" bit so that no future surveyor will think it was actually 2001 B.C and also enjoyed the mention that the whole business was conducted with a model of GPS system that only 13 years later is seldom seen outside of eBay, as if that somehow was a necessary qualification. Do wish that the author had mentioned what lunch consisted of that day, though.
Was it really true north or was it grid north?
Do you see many surveys that are actually on true north?
> Was it really true north or was it grid north?
Says true but likely grid. Can't be certain. That's the point. We can be fairly certain that the gonad who wrote it didn't know.
> Do you see many surveys that are actually on true north?
Not when done with RTK.
I would guess that it was true north at the longitude the base was set on to start the survey and then grid off that, if you know that longitude it's easy to get back on the bearings, and if it's a small lot type of survey then you can get on it anyway-not much convergence across a city lot;-)
But I'm guessing
A statement reflecting the actual process would probably be:
BASIS OF BEARINGS was established by single epoch rtk projected to State Plane using an incorrect datum of unknown epoch, then mutilated through a localization. I have no idea how to read or express what this thing tells me. For additional information contact brand X sales...
> I would guess that it was true north at the longitude the base was set on to start the survey and then grid off that, if you know that longitude it's easy to get back on the bearings, and if it's a small lot type of survey then you can get on it anyway-not much convergence across a city lot.
Yes, bearings appear to actually refer to true North at the meridian of the unspecified point where the base was set up. Since the tract is about four miles in extent East and West, the convergence is significant.
> Was it really true north or was it grid north?
It was roll-your-own North, i.e. refering to the direction of true North at an autonomous position somewhere within the project at an unstated longitude. It would not be completely unlikely that there are actually multiple bearing bases within the roughly twelve square mile project if multiple base station locations were used. I'm hoping not.
Yes, bearings appear to actually refer to true North at the meridian of the unspecified point where the base was set up. Since the tract is about four miles in extent East and West, the convergence is significant.
Yep!!
Four miles would be 3 about minutes here, a little less in Texas, but plenty of rotation with that one.
Ah well, early days of GPS RTK people doing things they just didn't really understand, handed a unit by a salesman and half a day showing how to "use" it.
Set up, do a "here", a no projection/no datum file and go survey-fun times!!
I think that "Basis of Bearings: Assumed". I think that is a lower wattage, at least the guy above sort of tried to tell you something.
I run into lots of "assumed".
N
> "BEARING BASIS derived from true North observations using G.P.S. (Trimble 4400) R.T.K. system the 12th of December, 2001 A.D."
During a trial for adverse possession, the other surveyor brought in his handheld garmin he used to locate the stumps... the judge was not impressed. I was relieved to know why our stump locations varied by so much.
To me, I don't really care. It's the same with using EDM's, tapes and whatnot. Usually find crap in a too many surveys. The fun is figuring out when, where, what and how. I once retraced a survey of a former employer and came back and told him what kind of instrument he was probably using and he had an offset correction problem with his measurements. He was quite surprised and asked how did you figure that out?:-O It gets easier when you've made just about every mistake there is with all kinds of equipment and experience.:-D Kent, with a basis of bearings like that it would be a challenge to me to calculate where the basis originated from.
Pablo B-)
Always such concerns over these bearing bases... I just punch in the plans, find some monuments, rotate accordingly. QED
> Always such concerns over these bearing bases... I just punch in the plans, find some monuments, rotate accordingly. QED
Well, the problem on a large project extending over many square miles is that someone who was so clueless as to create the prize-winning bearing basis note quoted above might also do various similarly clueless other things when the base was moved around on the project. I've followed surveys of similar size tracts where the bearings reported in different parts of the project referred to different "North" directions, apparently as a result of setting up the RTK base at several different places on surveyed coordinates, but screwing up the orientation of all of the vectors surveyed from each base.
Kent is right.... folks assume that "True North" means the same thing, no matter where they put their base.
It's a mess.
N
Wellllll...
IF.... (maybe big IF) the statement "True bearings,", is "TRUE"...then what is the problem?
Granted..."True Bearings" might be somewhat confusing in Texas where "bearings" (true or otherwise) is a whatever you want them to be (I guess), and therefore the concept of a "True Bearing" is somewhat ambiguous.
In the PLSS States, the concept is (or should be) well understood (and well defined in the LAW).
I'll stipulate that the "basis of bearing statement" as POSTED, is rather minimalist, but so are your North Arrows, but that's OKAY....
MOST... (yes MOST) of the United States was (as IS) based on "True Bearings" (and Distances) as defined by Federal Law. So "True Bearing" (astronomic or geodetic) is (or should be) a no-brainer.
Now whether or NOT, the author of the subject statement KNEW what he (or she) was talking about is another issue altogether.
IF he (or she) said:
"BEARING BASIS derived from Texas North Zone State Plane Coordinate observations using G.P.S. (Trimble 4400) R.T.K. system the 12th of December, 2001 A.D."
Then would you been any more confident with the data?
I hope NOT!!!!
But Texas...is well TEXAS, and that's you cross to bear.
B-)
Loyal
> IF.... (maybe big IF) the statement "True bearings,", is "TRUE"...then what is the problem?
Well, true bearings would be really dumb in Texas, for starters since the PLSS stops in Oklahoma.
> In the PLSS States, the concept is (or should be) well understood (and well defined in the LAW).
You're referring, of course to the cookbook that y'all have to follow up there in PLSSia, but which hardly anyone actually does? That's what I thought.
> I'll stipulate that the "basis of bearing statement" as POSTED, is rather minimalist, but so are your North Arrows, but that's OKAY....
Well, I'd hardly call it "minimalist". It probably seems so in comparison to the half page of metadata that all those customer projections used in PLSSia instead of true bearings require, but what is striking about the note is how rich with extraneous, useless detail it is, while saying nothing much more than "bearings sort of refer to a Northish direction, but I'm not telling"
> MOST... (yes MOST) of the United States was (as IS) based on "True Bearings" (and Distances) as defined by Federal Law. So "True Bearing" (astronomic or geodetic) is (or should be) a no-brainer.
Probably not really most of the United States, though, if you mean where the actual population really lives. I suppose you're just counting the acres of jackrabbits and sage brush in the empty quarter of the country, though.
> Now whether or NOT, the author of the subject statement KNEW what he (or she) was talking about is another issue altogether.
Not really, it's sort of the central point. :>
>
> Yes, bearings appear to actually refer to true North at the meridian of the unspecified point where the base was set up. Since the tract is about four miles in extent East and West, the convergence is significant.
While the bearing base may be a bit off, since it appears to be a "No Projection/No Datum" "Here" position, then translated to say 50,000/50,000, then yes there is a "mapping angle" at an unspecified point, but still shouldn't be too hard to replicate once two of the objects are located.
It seems to be a minor irritation at best. You would have done the same thing if the basis was "Bearings are assumed".
> > Was it really true north or was it grid north?
>
> It was roll-your-own North, i.e. refering to the direction of true North at an autonomous position somewhere within the project at an unstated longitude. It would not be completely unlikely that there are actually multiple bearing bases within the roughly twelve square mile project if multiple base station locations were used. I'm hoping not.
If it is your "worst case senario", then I agree that would suck bad since, they would never really tie together. Hopefully they just pushed their theoretical grid around and not made new autonomous positions at each base station.
The problem is that it indicates that the user does not know which meta-data was actually needed, which indicates that they may not PERSONALLY know what is going on.
N