"True North, by GPS observation".
My problem with this, is that it leaves the question hanging... does he even know what his Basis of Bearings are?
IF he sets his base up again, a mile east of it, to do another survey, and he uses the "Same" BOB, on the second survey, will he understand why the bearings on the 2 jobs are NOT the same?
Why not just use STATE PLANE GRID bearings, on both of them?
N
Because most deeds of record are not using STATE PLANE GRID bearings. It should be Geodict North instead of True North. The only times I come accross STATE PLANE GRID deeds are from the DOT, or other goverment projects. I pray lawyers don't start writing deeds using STATE PLANE GRID bearings. :-O
'tis the statement of an idiot, signifying nothing...
> "True North, by GPS observation".
State minimum standards require a basis of bearings statement. Why? I don't know. There is such a statement present, so the minimum standard is satisfied. Yet clearly the surveyor has no idea what his fancy box is telling him. And Surveyors get no respect as a profession. I wonder why?
It still leaves the actual BOB hanging. Depending on how far E or W of the survey his base is set up.
What would be wrong with State Plane Brgs, and ground distances?
N
What is "True North"... really...
I can't say I've always done this, but the wording I've evolved over the years is something to the effect of:
'Bearings based on a local grid having an origin of North Latitude: XX°xx'xx" and West Longitude: XX°xx'xx"'
and perhaps:
'as determined by [solar observations][GPS observations]'
The reason I stipulate "local grid" instead of geodetic is that I'm not reporting true geodetic bearings for each line. I have a bearing determined at some meridian and all of the other bearings are determined from turned angles from that meridian. I'm not applying convergence angles to each direction, so I'm actually creating a grid (even if it isn't a formal projection). I stipulate the origin by geodetic coordinates so that the convergence to another meridian can be determined mathematically. I sometimes add the method so that a future surveyor can estimate what my precision might be, although, I have recently done this less as I don't specify methods or technologies for any other measurement given on a survey.
Yeap, I see those all the time,"Bearings are based on GPS North". Question mark here! If you used RTK for the boundaries then it should be, Bearings are referred to grid bearings of the XXX Coord. System, NAD XXX, groung distances, unless you are using grid right out of the controller.
I was always taught that for a boundary survey your basis of bearing should be between two record monuments and be clearly depicted on the plat. When it comes to surveys other than boundary we state basis with complete description, - ground monument based or GPS and show control monuments. The bottom line is that a basis of bearing is better from ground based monumentation. I have found it very hard to just set up anywhere and try and re-establish a bearing from GPS observations done years previously. If basis of bearing is listed as GPS or True from GPS I don’t consider it dependable enough to stake out calculated points without first verifying it from ground control. I saw a case where a surveyor set up on a construction control point and started laying out plan coordinates based on the north his rtk unit decided to use that day. He justified the mess he made because the plan stated basis of bearing from GPS. The engineering company shrugged their shoulders and claimed ignorance and the client ended up eating the fixes. In the end everyone was shaking their head saying stupid surveyors.
I agree totally with Bear Bait.... bearing basis on boundary surveys should be based on observation or calculated bearing between two recoverable monuments shown on the survey. To refer to True North, Magnetic north, GPS North, Grid north, etc can add too much confusion to a lay person (and even some surveyors). If your survey is tied to State Plane Coordinates then so state and reference the monuments that located to tie into the state plane system for your area. Safest bet is to say it is a local grid system (even if it is not) and give a minimum of two on site monuments as control references.
Idaho Code (and several other State Laws) clearly require a line between two monuments to be labeled "Basis of Bearing". The purpose of that habit has evolved over time, but its importance hasn't diminished a bit.
For a few decades it was applied primarily to the line held in a compass adjustment. Go back a bit further and it was usually the line referenced in establishing and maintaining title for a particular parcel.
With the advent of GPS we saw dozens of these statements pop up. Unfortunately very few understood (or in some cases understand) what they are saying. We never said, "Basis of bearings established by Wild Total Station". I don't recall ever needing to rotate my local Deed to a set of CORS stations in the State next door either. In our desire to say things smart and fancy, we risk revealing the fact that some of us should read a book or two...
There is some value in stating the system your bearings are referenced to. I do it all the time. At the same time we should remember that our tools do not over-ride the historical purpose of a 'Basis of Bearing', or any other piece of information on our Surveys. It's about preserving evidence related to the establishment and maintenance of Title and making our Survey something that can be followed..
My .02, Tom
> Idaho Code (and several other State Laws) clearly require a line between two monuments to be labeled "Basis of Bearing". The purpose of that habit has evolved over time, but its importance hasn't diminished a bit.
Texas had similar wording but has since begun allowing the use of either a monumented line or "established geodetic system".
It's unnecessary to state a basis of bearing on a single line when the survey is related to the Earth's polar axis. No single monumented line in the survey has any more control weight than any other, unless you actually did your astronomic observation on that line or observed that line with precision GPS and turned angles to the rest of the monuments.
> "True North, by GPS observation".
>
> My problem with this, is that it leaves the question hanging... does he even know what his Basis of Bearings are?
>
> IF he sets his base up again, a mile east of it, to do another survey, and he uses the "Same" BOB, on the second survey, will he understand why the bearings on the 2 jobs are NOT the same?
>
> Why not just use STATE PLANE GRID bearings, on both of them?
>
>
> N
Here's what we used on our drawings when going to a GPS system.
BASIS OF BEARING
ASTRONOMIC – DERIVED FROM GLOBAL POSITIONING SYSTEM
OBSERVATIONS. ALL LINES HEREON STAND ALONE AS A TRUE
SURFACE BEARING
"True North": vs .......
"False North"?? Sort of like "True Point of Beginning"..... what, was there a false one??!!:-S
-JD-
Without full meta data this is just a problem waiting to happen.
Monuments tied, record coords, epoch, all that stuff.
My bet is that the answers to the above cant be readily answered... just another Black Box RTK crap job.
> Idaho Code (and several other State Laws) clearly require a line between two monuments to be labeled "Basis of Bearing". The purpose of that habit has evolved over time, but its importance hasn't diminished a bit.
>
> For a few decades it was applied primarily to the line held in a compass adjustment. Go back a bit further and it was usually the line referenced in establishing and maintaining title boundaries for a particular parcel.
>
> With the advent of GPS we saw dozens of these statements pop up. Unfortunately very few understood (or in some cases understand) what they are saying. We never said, "Basis of bearings established by Wild Total Station". I don't recall ever needing to rotate my local Deed to a set of CORS stations in the State next door either. In our desire to say things smart and fancy, we risk revealing the fact that some of us should read a book or two...
>
> There is some value in stating the system your bearings are referenced to. I do it all the time. At the same time we should remember that our tools do not over-ride the historical purpose of a 'Basis of Bearing', or any other piece of information on our Surveys. It's about preserving evidence related to the establishment and maintenance of Title boundaries and making our Survey something that can be followed..
>
I agree.
BASIS OF BEARING
ASTRONOMIC – DERIVED FROM GLOBAL POSITIONING SYSTEM
OBSERVATIONS. ALL LINES HEREON STAND ALONE AS A TRUE
SURFACE BEARING
This statement is very confusing to me. True bearings are based on the north pole.
According to the different GPS equipment I have used over the last 15 years the north pole seems to be moving.
Wouldn't you need to list backward and forward bearings to accomplish this statement?
This is not a very easy thing to repeat for future surveyors; sometimes I think that’s why some surveyors use these statements on plats. If you confuse everyone it is harder to prove errors.
Is it not the practice anymore to rotate survey to record so you may have a chance of retaining some record calls or does every survey totally change record?
> What is "True North"... really...
I think "true north" is (or was) the direction toward the north pole as opposed to the magnetic pole. (ie when using a compass, did you dial in the correction to read corrected bearings, or did you run it using the readings from magnetic north). But your point is well taken, especially these days where we have different "norths" based on different methodologies.
> Here's what we used on our drawings when going to a GPS system.
>
> BASIS OF BEARING
>
> ASTRONOMIC – DERIVED FROM GLOBAL POSITIONING SYSTEM
> OBSERVATIONS. ALL LINES HEREON STAND ALONE AS A TRUE
> SURFACE BEARING
I appreciate you being brave enough to post your phrasing, and I don't mean this to be a flame, but what you said doesn't make any sense.
Astronomic? - this refers to bearings determined by terrestrial observations (ie theodolite) of celestial objects (sun, stars, etc.) Astronomic differs from Geodetic by the Laplace correction, which is the effect of gravity on the level of your instrument. (Basically it is "out of plumb" to the ellipsoid).
True Surface Bearing? "True" is ambiguous, but generally is understood to be a geodetic bearing. So you've said bearings are astronomic and geodetic. This is contradictory. The variation in the two is slight, but they are two different things. What is a "surface" bearing?
> According to the different GPS equipment I have used over the last 15 years the north pole seems to be moving.
The change in earth tilt is extremely slight. You aren't seeing it with GPS equipment. A quick look at HTDP suggests it's moving a couple of centimeters per year.
I appreciate you starting your comment with thanking Charles about posting phrasing. I second that, thank you Charles for posting on this, any comments are not personal but in an effort to help all surveyors perpetuate their own work.
Shawn, you misinterpreted my comment on the north pole, I believe the north pole is probably pretty close to where it was when I started using GPS 15 years ago and the changes are a function of different models, epochs, cors stations and inherent equipment errors and differences. I am not confident enough to believe that the numbers the equipment is giving me are gospel for all times and that I am considering every aspect of GPS reduction every time I use the data.
If someone has control that they have used for 15 plus years that was established originally by GPS methods and they have the same bearing today with modern GPS as they did originally then I would love to hear about it.
