I'm working on a project that has required attempting to reconstruct various parcels that were all surveyed in relation to a variety of essentially assumed bearing bases between 1950 and 2010. They all were mainly done plucking the bearing between pairs of survey markers then in place from the cadastral ether of prior conveyances and just assuming that bearing was correct for all time.
Fast forward nearly a decade and many of the survey markers have been destroyed, thus returning the supposed bearing basis to the ether. It would have been so much more useful to have adopted some bearing basis like astronomic/geodetic North or grid North that declining to do so borders on negligence.
I hope that the surveyors who are continuing the practice of just creating their own private "North" directions from the rumored bearings between pairs of perishable monuments on the theory that modern life won't destroy the monuments rethink this in the new year, particularly the GPS users who have the means at hand to do much better for essentially zero additional cost.
It Depends
A significant amount of the work I do involves small lots in an urban environment featuring lots of buildings and broad-canopied trees. A fairly dense network of recorded survey marks referenced to a bearing base established over a century ago makes it easy to continue to reference surveys to that orientation.
I *could* set up a pair of GPS receivers in some offsite location with decent sky view and tie them into my control network, thus enabling the use of a NAD83 basis of bearings, but I can't think of a good reason for going to the extra expense only to have my map stick out like a sore thumb from all the others in the vicinity.
As with many things, it depends.
It Depends
> A significant amount of the work I do involves small lots in an urban environment featuring lots of buildings and broad-canopied trees. A fairly dense network of recorded survey marks referenced to a bearing base established over a century ago makes it easy to continue to reference surveys to that orientation.
Well, if you have indestructible survey marks from which to take a bearing basis, that's different. I have have heard about such things but thought they were all just one public works project away from extinction.
If a location isn't GPSable and the project extents are urban small, solar observations should give nearly as good or better an azimuth solution for about the same amount of time on station as GPS would have.
It Depends
> I have have heard about such things but thought they were all just one public works project away from extinction.
It's true that construction projects have kept things interesting in our little downtown. Within the last year I've had to replace at least a dozen corner marks that fell in the path of progress. The good news is that I was paid to replace almost all of them.
I'm slowly getting the PW folks to actually pay attention to their legal obligations in that regard, but I'm having to fight many decades of tradition in doing so. My hope is that some day they'll actually add "identify, reference and replace survey markers" to their project planning and post-construction checklists.
We still put the majority of our jobs on "True Bearing" via sunshot. It never ceases to amaze me how the majority of lines we re-tracce from the late 1800's and early 1900's are usually within 10 minutes of "True", and yet the lines run from the 1970's to present can vary up to 6 degrees.
Bruce
That would allow re-running a line by direction without taking into consideration other evidence. The same can be accomplished by just using coordinates, regardless of what the bearing basis is. Of course it makes sense to do as you say; it's cleaner and nicer for those following. But I'm not sure I see the level of importance you are placing on it.
I agree that assumed bearing basis is nearly worthless, unless, when following in the footsteps of the previous surveyor, one can find two, preferably more, of the original monuments. When following in the footsteps of the original surveyor, we must orient our new work to that of the original surveyor, or risk getting lost in the woods.
Since most of my work is now in New Hampshire, where all the land was surveyed at some point in time, I always state on my plan what the basis of bearings is (magnetic, recorded plan, Highway layout, etc.). The only time I base my bearings on NH-Grid, GPS, True, is when some regulatory agency mandates that I do so.
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.
It Depends
I hear that same argument about changing the basis of bearings on many surveys. Why change it? My argument is that bringing the system to grid will allow for reestablishing the monuments even after the government stops funding replacing the local monuments.
I pretty much agree with Kent...
I realize that folks who work in Urban/Residential environments (i.e. DOWNTOWN) see the world from a different perspective, but that doesn't mean that such a mind-set should be transferred to areas where it is not well suited or applicable.
I have been “fighting” several 'surveys' recently where “Downtown Surveyors” have ASSUMED Bearings between Monuments (PLSS Corners) that have since disappeared without a trace.
A Solar, Polaris, or tie into the NSRS (NAD_whatever) would have perpetuated the “Basis of Bearing” for posterity, instead we are left with an ambiguity that is both troublesome AND unnecessary.
I submit an excerpt from the Manual of Survey Instructions, Edition of 1894:
Page 71:
EXPLANATIONS OF THE ARTICLES ON PAGES 72 to 78, WITH GENERAL DEFINITIONS OF A "RETRACEMENT" AND A 'RESURVEY.
Paragraph 6:
"In order to prevent any misunderstanding relative to the modus operandi indicated by the terms 'retracement' and 'resurvey,' the following definitions of the same are here presented:"
Paragraph 7:
"The retracement of a township boundary, or other line of survey, consists in the determination of the true bearings and distances between the successive corners along the entire length of such line; and the data thus obtained will be embodied in the field notes together with the detailed particulars of the methods employed."
Paragraph 8:
"The resurvey of a township boundary or other line of survey consists of a retracement of such line accompanied by the reconstruction of defective original corners and the establishment thereon of all the necessary new corners, and the detailed particulars of the entire operation will be embodied in the field notes."
Now MOST folks “out here,” seem to have no problem with returning “measured v. record” DISTANCES, but virtually NONE of them “dare” return measured v. record BEARINGS (True, Geodetic, Grid, whatever), accompanied by the requisite metadata to reproduce said Bearings.
It makes one wonder...IF 'they” are uncomfortable about their ability to determine a scientifically reproducible BEARING, then why should I have any confidence in their ability to measure a distance either?
Loyal
> That would allow re-running a line by direction without taking into consideration other evidence. The same can be accomplished by just using coordinates, regardless of what the bearing basis is.
Well, if you can't reproduce the orientation of the coordinate grid, what good do coordinates do? The advantage to being able to know with very small uncertainty what the actual directions of lines run were is it allows a retracing surveyor to efficiently winnow out the chaff of conflicting evidence that accumulates over time. Markers get displaced by construction? Check. New markers get placed in ignorance of the originals still in place? Check. Stuff happens? Check.
Assumed Bearing Basis? Because You Have To Start Somewhere
Quite a few of my projects begin with a variety of assumed bearings.
I start by plotting every deed as is, creating polylines for each.
Then one fits the puzzle together, sometimes on the PQ assumed bearing or possibly that of an adjacent filed map or even deeded subdivision that has one bearing system.
Then one goes to the field to look for evidence, for gores and overlaps one looks both ways beyond obvious corners for markers. It is possible on a completed survey that every line has a reference to a different deed.
It is easy to have 2 days in the office and a day in the field before you have enough data to even hold one line. Once you are done it is usually neccessary to return to the field to search for contrary evidence, where it appears it should exist. The acreage covered far exceeds the PQ area.
It is no fun if it is too easy.
Paul in PA
>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.
Is the idea that magnetic North is constant and unchanging in New Hampshire? Somehow that seems unlikely to hold for very long. Why isn't it good enough just to note the magnetic declination at the time of the survey and give a little recipe for converting true or grid bearings to approximate magnetic bearings? I can't see a magnetic bearing basis as being all that useful to a future surveyor who is surveying an adjoining tract and wants to locate the boundary with certainty and as little fuss and muss as possible.
> Even LHA is easy to do, quick and effective
Landing Helicopter Assault? Local Housing Allowance? Livonia Hockey Association? Lateral Hypothalamic Area? Left Handed Anus?
They all seem kind of difficult to incorporate into my urban jobs. Guess I'll just stick with the monuments.
I rotate and translate, then use the GPS with Grid North and some out pretty close to the original monuments.
Even state plane coordinates are monument dependent.
I have extensive experience with state plane coordinates in various neighboring municipalities. Each one is RIGHT, and they all are carefully tied to monuments on the ground.
Each its slightly different. Each is close to an OPUS solution, each is carefully defined by the realization of the NAD, and the epoch.
But...in reality each of the municipalities have their own datum, which is more or less closely tied to state plane.
The same is true of each of your surveys that hold state plane bearings.
We are surveyors, and no matter what: monuments matter.
That being said, reference to state plane may end up being the best evidence of where those monuments were. This is a good thing, and I agree it is a good idea.
So perhaps publishing actual vectors from a CORS would be better?
Question about True North Surveys?
To those of you that reference your surveys to true (or astronomic) north. Do you adjust all of your bearings in the survey to account for meridian convergence (i.e. true geodetic inverses throughout)or is it only true at one meridian on your survey?
Question about True North Surveys?
Well, as you know, truth is the first casualty of war. And, such is the case here. TRUE is only true at the Longitude of solar observation.
When GPS came along, and folks began MOVING their base station, in an EW direction, they were once again at a loss for words.
So, True north, is rarely true north, EXCEPT at a particular Meridian line.
Well, with that argument, ALL my maps, even the ones on MAGNETIC, are on true at SOME meridional line!
Now, if I were king, I'd require that the LONGITUDE of observation be PUBLISHED when using TRUE for Basis of Bearings!
Or STATE PLANE GRID Brgs.
Trouble maker Nate
Question about True North Surveys?
> Well, as you know, truth is the first casualty of war. And, such is the case here. TRUE is only true at the Longitude of solar observation.
>
> When GPS came along, and folks began MOVING their base station, in an EW direction, they were once again at a loss for words.
>
> So, True north, is rarely true north, EXCEPT at a particular Meridian line.
>
> Well, with that argument, ALL my maps, even the ones on MAGNETIC, are on true at SOME meridional line!
>
> Now, if I were king, I'd require that the LONGITUDE of observation be PUBLISHED when using TRUE for Basis of Bearings!
>
> Or STATE PLANE GRID Brgs.
>
> Trouble maker Nate
Here in Florida we have a lot of Florida Department of Transportation Right-of-Way maps that list their bearings as true. I have never checked them, but I have doubted if they really were true everywhere or just where they took their astronomic azimuth at for the particular project. At least with SPC you know that the bearings are true at the central meridian of the projection.
Question about True North Surveys?
Typically the basis of bearings note states which corner the solar observation was taken at or nearby.
Polaris is really easy to use for an astronomic bearing.
I think I will go out this afternoon and see if I can find it because the Sun is about as low in the sky as it is going to get.
Even then it is usually visible by the time gets about to the horizon even in the summertime.