Basis of bearings:
Geodetic north, as taked at 3 different base stations, in the general area of this project. (You retrace me, and figure out which one was done from where)
🙂
Nate
It's up on the drawing. What else do you need to know?:-D
Or: "Bearings are based on GPS observations"
So........
Basis of Bearing ASSUMED
My point is that Some surveyors are MIXING geodetic brgs, and rectangular coords, without knowing it.
N
Nate
I wouldn't be surprised one bit.
If there is a way to screw something up, someone will do it. And if there isn't currently a way, they will invent one.
But bear in mind, MODERN BLM Cadastral Plats return Geodetic Bearings, and some Private Record Of Survey Plats do too (including one I will file this month).
Loyal
Nate
If your basis of brgs is Geodetic, then it is ONLY at that longititude. IF you change your base, E-W, then you will have to throw a theta at it, to maintain parallel brgs to your previous base. Some GPS users don't realize it.
N
Nate
That's true IF you are playing with rectilinear coordinates.
The PLSS is based (and platted) in a geographic [geodetic] system.
Parallel lines (other than due East-West) have different bearings.
Loyal
In Florida...
The bearing or azimuth reference shall be
clearly stated on the face of the plat in the notes or legend,
and, in all cases, the bearings used shall be referenced
to some well established and monumented line.
Add this to your states MTS.
:coffee:
In Florida...
Well established and monumented line?? Once again, what about GRID brgs?
Central Meridian in Arkansas is in the middle of the state. All you have to know is Lat Lon, and from this you can derive Theta.
IS the Central Meridian WELL ESTABLISHED? yes. Monumented? Don't think so!
:0)
N
In Florida...
Well established and monumented line?? Once again, what about True brgs?
True (Geodetic North) is EVERYWHERE. All you have to know is Lat Lon Time, and from this you can derive NORTH.
IS the Geodetic North Pole WELL ESTABLISHED? yes. Monumented? Don't think so!
Basis of Bearings = The Sun!
Basis of Bearings = The Moon!
Basis of Bearings = The North Star!
Basis of Bearings = GPS Observations!
Basis of Bearings = The NGS Passive Network!
🙂
L
fer Nate
There is no question but what “True Bearings” are a bit of a PITA at times, but they are pretty unambiguous. Sure...you can argue Astronomic v. Geodetic, and NAD27 v. NAD83, but reasonable metadata resolves that from the get go.
Those of us who work in the PLSS have been dealing with “True Bearings” since day one, so we should all have a pretty good handle on it by now.
I am NOT suggesting that every Record of Survey, Description, residential Subdivision (or anything else) be returned (platted) in “True Bearings!” It would only make matters worse (and drive the plat-checkers and GIS folks crazy[er])!
I DO BELIEVE that using a scientifically derived Basis of Bearings (SPC/UTM/LDP) that can easily be reproduced INDEPENDENTLY of the physical monuments is a GOOD idea. But I also think that the requisite information to compute the “True Bearing & Distance” (as per the Manual) be included on any survey, plat, ROS, whatever (residential subdivisions, urban surveys and many engineering projects may or may not benefit from this).
I also like giving Nate a little crap because...I like him, and he's a pretty good sport about it!
BTW...I only RARELY return "True Bearings/Distances" and ONLY when I have a good reason for doing so.
Loyal
fer Loyal
"reasonable metadata"
Yeah.
Right.
Plat I's lookin at rat now it say:
"Basis of Bearings GPS/True."
An thets it.
N
fer Nate
I see those too!
There ain't no fix'n stupid!
Maybe it's the high cost of Printer/Plotter Ink that is the real culprit.
🙂
Loyal
Mr. Loyola....
My position is:
(State Law should be:)
All Survey plats in the State of Arkansas shall be referenced to an objective Basis of Bearings, in a repeatable manner. *
* Objective Basis of Bearings means either State Plane Grid Bearings, or Geodetic North.
In cases where another brg system is established, such as previous plat or deed, may be used, so long as the rotation to State Plane Grid, or True is shown. If Geodetic, is used, then the Longitude where such brgs is derived, shall be shown, or posted on said plat.
------------------------------------------------
And, this would become an acceptable BOB:
Basis of Brgs, taken from the previous survey by Fred Jackson, PLS xxxx, between the NW corner, of Section 37, and the W1/4 corner of the same. For Geodetic North, rotate these brgs CCW 1°39'14". Geodetic north was observed at a point 100' East of the NW corner of said S37, as shown on this plat.
We are not idiots. but, To require that all surveys show an objective BOB is not too much.
Nate
Mr. Loyola....
Are we talking about Geodetic north at some longitude and then grid east and west of that longitude?
So basically a Local Projection centered on that longitude?
Or geodetic north (or true north, or astronomic north) for the entire project; like the PLSS and many old highway and railroad surveys.
Because if I see Geodetic North as a basis on a plat I'll assume all bearings are given as Geodetic North even though I'll probably find it's really a grid.
How about this:
Bearings are grid: Grid North=Geodetic north at Longitude 100degrees 00' 00"W NAD83.
Mr. Loyola....
I pretty much agree with Nate's suggestions above, although I would add UTM Grid, City/County Grid, or any properly defined LDP to the "options."
Mighty...I dunno...without some [MORE] clarification about the origin and geometry of the "local grid" (like the projection parameters, mean Height, Datum, etc. etc.) we get back into the same ol 10k/10k on yonder hill mess.
I prefer to work in a rectilinear coordinate system as much as the next guy, but far too many folks fail to leave any coherent “geospatial footsteps” for others to follow.
Loyal
