"Bases of bearings: Astronomical GPS used"
?ÿ
Just found this on a fairly recent(2014) map - and he recorded it!
It must have been one of those really expensive units.
I'd like it to be State Law, in all states that:
Spc be used as BOB on all surveys. Proper zone shown.
Or if it's not, then theta or convergency angle shown.
Or, if not, and "true" or geodetic is used, then the lat lon where gps was set up must be shown.
Or Lat Lon where solar obs was taken be published. If true north was not used, then the correction angle be shown.
Before I die.... Or retire!
N
🙂
If I say that line is assumed to be "north".............accept it as not being spc or anything else. The relative bearings will get you to the monuments..........every time.
I agree with His Bovineness, knowing a bearing for a particular line is more useful than knowing how bearings were arrived at.
Knowing that bearings were somehow derived by GNSS or astronomically and expressed as true or SPC or LDP without knowing?ÿ which line on a large plat was held is ambiguous, because of convergence.
It does save confusion, though, if it is noted when grid distances are given instead of ground.
If the map is on true, it's on true. It will have apparent mis-closure. Latitude is required to treat it right, but long is not.
If one line is shown as true, the point where convergence is computed is needed, but that does not equate to a 'basis of bearings' being 'true'. It will give you one 'true' line as long as you run it the right direction.
I do most of my jobs on SPC grid, but recognize the value of using a different line in some cases. Policy that forces an 'spc' work flow is a grotesque overstep. Sometimes a few 90's in the front and back with a drag chain for distances is more efficient than setting up a file in a data collector. Stripping that option away is wrong.
He added an "Approximate Section Line", labelled with a bearing, but no monuments, and no ties from it to anything. That cleared things right up!
Astronomical GPS used
That's like pretty ugly, doesn't make sense but I know what you mean.?ÿ
Obviously using the second definition of Astronomical per Webster: ??enormously or inconceivably large or great?.?ÿ
?ÿ
@MightyMoe you are right. We know what was meant... (I think!)
Clear understanding and articulation of metadata though, should be a part of what we are.
The fellowship of other surveyors is something I've come to appreciate.
N
absent full metadata it is a worthless statement.... but Basis of Bearing is not relevant in the modern world anyway, so who cares.
absent full metadata it is a worthless statement.... but Basis of Bearing is not relevant in the modern world anyway, so who cares.
I do - my State requires that a Basis of Bearings be shown on all maps...
Basis of Bearings is a minimum standard requirement for maps in all the states I'm licensed in, and reviewers tend to zero in on it. Former County Surveyors had unrealistic expectations regarding BOBs. The current occupants of the offices have adopted a much better attitude. But, to me, it's either on a grid system or it's not.?ÿ ?ÿThe thing about the statement the OP quoted is the shocking ignorance it exposes.
Here in the Portland/Vancouver area there are still a lot of companies that do not have GPS. I believe that is the case in Seattle/Tacoma and other urban areas of the PNW as well.?ÿ Without GPS putting a job on SP (or, in the case of Portland, OCRS) is impractical.?ÿ ?ÿSo you aren't likely to get a BOB on SP law enacted around here.?ÿ Still, it's a good idea to put a job on grid - if for no other reason than it simplifies the BOB statement. I do it most of the time. Nevertheless there are many cases where the tree cover is simply too dense to use GPS effectively.?ÿ
Let me put in a plug here for Low Distortion Projections. It's the way to go. If your state doesn't have them you should be asking why not.?ÿ ?ÿ
I'd like it to be State Law, in all states that:
Spc be used as BOB on all surveys. Proper zone shown.
Or if it's not, then theta or convergency angle shown.
Or, if not, and "true" or geodetic is used, then the lat lon where gps was set up must be shown.
Or Lat Lon where solar obs was taken be published. If true north was not used, then the correction angle be shown.
Before I die.... Or retire!
N
🙂
As thebionicman said I think requiring state plane is unnecessary and adds a significant burden to some surveyors with little benefit.?ÿ
I think what you are referring to as "true geodetic" is actually a local plane based on true geodetic bearing at one point. "True" geodetic bearings are independent of the location of the GPS. If I had my way we would all be using true mean bearings, while this involved a lot heavy calculation in the old days, our modern software makes it effortless, and that way we wouldn't have to worry about scale factors, and the 1/10,000 loss of accuracy.?ÿ
absent full metadata it is a worthless statement.... but Basis of Bearing is not relevant in the modern world anyway, so who cares.
There is often a lot of irrelevant information in basis of bearing statements, but whether a survey is on some sort of plane, or true mean geodetic bearings is very relevant.?ÿ
I'd like it to be State Law, in all states that:
Spc be used as BOB on all surveys. Proper zone shown.
Or if it's not, then theta or convergency angle shown.
Or, if not, and "true" or geodetic is used, then the lat lon where gps was set up must be shown.
Or Lat Lon where solar obs was taken be published. If true north was not used, then the correction angle be shown.
Before I die.... Or retire!
N
🙂
As thebionicman said I think requiring state plane is unnecessary and adds a significant burden to some surveyors with little benefit.?ÿ
I think what you are referring to as "true geodetic" is actually a local plane based on true geodetic bearing at one point. "True" geodetic bearings are independent of the location of the GPS. If I had my way we would all be using true mean bearings, while this involved a lot heavy calculation in the old days, our modern software makes it effortless, and that way we wouldn't have to worry about scale factors, and the 1/10,000 loss of accuracy.?ÿ
But if true bearings and surface distances are used, then how will a closure be calculated??ÿ ??ÿ
After all that's what is most important.?ÿ
I've sure considered doing it for some larger plats. Heck a good sized subdivision would make a perfect "true" survey. You could trigger lots of checkers doing that.?ÿ
absent full metadata it is a worthless statement.... but Basis of Bearing is not relevant in the modern world anyway, so who cares.
There is often a lot of irrelevant information in basis of bearing statements, but whether a survey is on some sort of plane, or true mean geodetic bearings is very relevant.?ÿ
"absent full metadata it is a worthless statement...."
The Reason for a Basis of Bearing note is so that it can be repeated, in the same Position on The Ground, many years into the future. It came from the day of Compass, and was well understood...
Methods have changed, but the desired result remains... the term "Basis of Bearing" is archaic.
"Autonomous" ?
The Reason for a Basis of Bearing note is so that it can be repeated, in the same Position on The Ground, many years into the future. It came from the day of Compass, and was well understood...
Methods have changed, but the desired result remains... the term "Basis of Bearing" is archaic.
You are right the term is?ÿ often misused, but there a still plenty of total station (and GPS) surveys being done that use a record line as their basis. Even with a "GPS basis", We still need some the information usually included under that header. Maybe we should just start calling it a "bases of bearing" statement in recognition of that.?ÿ