Grid Basis of Bearings

[Dave Karoly, PLS]

I would appreciate a succinct statement of what is required to state a grid basis of bearings per CCS83. No statement of coordinates is being made.

[Double_Proportion]

It's Sunday so I'm not going to look it up. Offhand I believe based on the public resource code you need to show coordinates, a control scheme, convergence at at least one point and epoch. Hope this was helpful, again its Sunday, I may be mixing and matching tidbits of information.

[dmi]

If you are are using CCS83 and reporting CCS83, then you must follow the Public resources code.

[Jim Frame]

If you're not actually disclosing any CCS83 coordinates in connection with your survey, then PRC §8801 et seq don't pertain, so you're free to wing it.

Assuming a survey oriented solely by means of GPS observations and not tied to CSRN, something along the lines of following ought to suffice:

"The basis of bearings of this survey is the California Coordinate System of 1983, Zone 2, as determined by GPS observations."

There's a lot of information that's *not* contained in the above (e.g. that you used survey-grade receivers and competent ephemerides -- preferably IGS rapid or final -- and that you have enough redundant observations to ensure conformity with the standard of practice), but then that's true of almost any survey.

P.S. This post made me aware that I released a map last week that's not in compliance with the PRC. It's referenced to the UCD campus control system -- which is nominally CCS83 Zone 2 -- and discloses coordinates, but because I was thinking *campus* control and not CSRN, I only showed a tie to one CSRN station (UCD1). I guess I have to send out an addendum now to comply with the statute. Rats...

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[Stephen Johnson]

If you're not actually disclosing any CCS83 coordinates in connection with your survey, then PRC §8801 et seq don't pertain, so you're free to wing it.

Assuming a survey oriented solely by means of GPS observations and not tied to CSRN, something along the lines of following ought to suffice:

"The basis of bearings of this survey is the California Coordinate System of 1983, Zone 2, as determined by GPS observations."

There's a lot of information that's *not* contained in the above (e.g. that you used survey-grade receivers and competent ephemerides -- preferably IGS rapid or final -- and that you have enough redundant observations to ensure conformity with the standard of practice), but then that's true of almost any survey.

P.S. This post made me aware that I released a map last week that's not in compliance with the PRC. It's referenced to the UCD campus control system -- which is nominally CCS83 Zone 2 -- and discloses coordinates, but because I was thinking *campus* control and not CSRN, I only showed a tie to one CSRN station (UCD1). I guess I have to send out an addendum now to comply with the statute. Rats...

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Jim,

That is what I classify as an "Uh-Oh" on the error scale. I developed it nearly 40 years ago while working construction.

It is as follows:

Un-Oh: You catch the mistake and nothing extra has to be done by others to fix it.
Mistake: Some one else finds the mistake and nothing or little has to be done to fix it.
F***up: It gets poured. OOPS!!! Someone goes out the gate and doesn't get to come back in.

[Dave Karoly, PLS]

I am aware of the PRC sections regarding CCS83, etc. I have read it numerous times. That wasn't the point of the thread.

I work all over the State. I have noticed some variation in the interpretation of the PRC.

That is why the question? Succinctly state (if you are interested) what you think must be shown on the face of a Record of Survey when using a Grid Basis of Bearings. Assume no accuracy is claimed.

This is not a command, you don't have to do it on Sunday morning or even during the cocktail hour if you don't want to.

[dmi]

I understood your question., But now you are asking a different question, a grid basis of bearings without reference to CCS83 would have a different succinct Basis of Bearings statement than one stating CCS83.

You are correct there is a wide variety of BOB statements around the state, but that is not the question you asked to start with.
Since you know all about the PRC, then you ought to know how to write a proper BOB statement, except for the occasional laspe as indicated by MR. Frame.

[Scott Tikalsky]

Dave,
While sitting at a watering hole in Monterey several years ago, a discussion, among several learned surveyors, broke out on the subject of bearing basis statements (Yes, I do believe Heinekens were involved). One of the elder statesmen of the group made the comment that you could use “the moss growing the north side of the old oak treeâ€￾ to reference your bearing basis. As long as you give an identifiable point(s) and a reference direction, and the survey is retraceable, there should be no discord with state law and acceptable survey practices.
I am assuming you are setting your CCS83 bearing basis using GPS methods. On several occasions I have used the same method due to not having anything of record, close enough to reference to. Instead of calling it a grid basis of bearing based on CCS83, I have stated the bearing is based on GPS observations. Obviously, I also identify which 2 monuments are being used and state the bearing.
I have read the pertinent PRC sections several times over the years and also feel that this applies to stating coordinate values.
Just my 2 cents worth. Hope this helps you.
Ooops, missed the succinct part.

[Oxnard Kurt]

Not sure if required in your case but it sure would be helpful to other surveyors if you included the cgf ( combined grid scale factor) if you have it. And if you don't, I think you should get it.

So the next surveyor can convert it to ground.

Infact, Why don't you just convert it to ground yourself and use it, call out your reference and say "Converted to Ground per ...."

It is just a conversion, like meters to feet.

[Dave Karoly, PLS]

I agree with everything Dave Wooley said.

On smaller projects I choose a specific point on the map for stating the combined factor.

On larger projects I think it is best to leave them in grid.

[Dave Karoly, PLS]

Feel free to criticize it:

I am only talking about a grid basis of bearings. Everything else is at ground level. Coordinates are not stated. No accuracy is claimed for the grid basis of bearings.

First: We must comply with PRC 8813.1 (a) which requires that we tie the survey to control stations which meet certain requirements stated. Since we are not claiming an accuracy 8813.1 (b) does not apply.

Second: PRC 8813.2 does not apply because we are not claiming an accuracy for our grid bearing.

Third: We must comply with PRC8813.3 which requires that we show the values for the published control stations used including at least published accuracies. I realize there may be a thought that since we show a published accuracy then PRC 8813.2 is triggered; I don't think so because it starts with "if." The legislature put "if" in there which I take to mean there is a case in which 8813.2 is not required. It seems logical that stating an accuracy on a new value (such as a grid bearing) is optional and no accuracy is stated then PRC 8813.2 is not triggered.

To summarize it seems to me that at a minimum this information must be provided: 1) Control stations used (such as published CSRN stations) must be listed, their coordinates (north, east, elevation), their published accuracy, datum (for example CCS83), zone, epoch. 2) The statistically independent ties to the above control (or reference) stations must be stated or shown. The ties shown are the adjusted value. 3) The datum, zone & epoch of the grid bearings on the survey and the mapping angle.

Hopefully I didn't miss anything.

[Jim Frame]

Here's my critique:

I don't agree that §8813 applies. Both §8813.1 and §8813.3 state that "any survey that uses or establishes a CCS83 value or values shall" comply. Since you're not publishing CCS83 values, you're not disclosing any usage or establishment of CC83 stations, even if the survey is tied to some via data and calculations not shown on the face of the survey. (Conceptually, the CCS83 data constitutes field notes, which aren't part of the published survey documents.) You can get a CCS83 orientation well within the noise level of the technology by using an autonomous (non-CCS83) position from which to establish your survey, so ties to CCS83 aren't necessary anyway if all you're interested is orientation.

I have nothing against going the extra mile to show your CCS83 ties and associated metadata, I'm just point out that it's not a legislated requirement given the scenario you described.

.

[JoeC]

Okay – here is my two cents.

Why are you using two different datums on your map? Grid for a BOB and everything else is to ground.

Why not just convert you BOB to ground and show grid in parenthesis?
As you can see it does create a great deal of discussion and some confusion.

Sorry - I must be missing something.

[Dave Karoly, PLS]

Jim Frame-
Your interpretation is what I will call the Northern California interpretation, that is, value essentially means a coordinate. Of course you are absolutely correct that you can hit "here" on the base and it won't make much difference on the bearings you get. I went 8 miles one time in Nevada County (two HPGN stations) and the raw bearing out of the processing software was 1" different from the bearing derived from the published coordinates of those stations.

This thread was prompted by a question from another Surveyor I work with. He is encountering what I will call the Southern California interpretation, that is value is any CCS83 value including grid bearings. The rub seems to be the interpretation of the word "value."

Dave Wooley-
I understand what you are saying. In this case it's a very small survey of a 3 acre parcel and the difference between the true ground values of any two lines is very small. Over a larger area then it's best to stick with grid. Personally I would just use geodetic north and call it good but he chose to use grid north.

In this case the bearings and ties to CORS stations some distance away are really just incidental to the boundary survey shown. It is supplemental information that you would think would be good information to have as long as it is stated how it was derived. Maybe we should seek to add a section to the statute to allow for supplemental information to be shown if it is incidental to the Survey with a lot less need to debate what the Statute means.

[Steve Martin]

Attached are a couple ROS examples. I like to show a Control Diagram to show how the CCS83 Basis of Bearings was brought into the site.

On one I do show establishing coordinates on 1 point, but usually the diagram is just there to help the reader evaluate the relative strength of the survey and aide in retracing it.

For what its worth,

[Steve Martin]

The symbol is supposed to represent a GPS antenna with tripod and lightning bolts comming out of it. I'll have to refine it a little.

I have a ton of first order Record of Surveys in San Diego County with the vectors labeled including the day and session ID for each measured vector to meet the requirements if PRC 8813(c)

[Rob_LS]

Dave W - A minor clarification to a portion of your CCS explanation. "The mapping angle is a constant applied to the difference in longitude." For each point of a given longitude in a CCS zone, the mapping angle is the same. Change your longitude, and the mapping angle changes.

Also, you (Dave W) may get arguments regarding: "there is no more of a pure and repeatable measurement than a grid measurement" without further clarification. I'm assuming you are referring to repeated post-processed static GPS having fairly long distances between points measured within a period of time having negligible amounts of episodic and secular ground (tectonic) motion.

Dave K - If you "would just use geodetic north and call it good" as opposed to using grid how would you determine what geodetic north is on your project? In other words, what is the basis of your geodetic directions you are stating? I'm not doubting your methods, just trying to understand how someone else can retrace your survey?

And do we need additional laws "to allow for supplemental information" or is it up to the PLS to provide any supplemental info he or she deems is worthwhile showing on the R of S?

[Dave Karoly, PLS]

Someone else could retrace my survey from the found and set monuments on it.

What I call the bearing from Monument A to Monument B is somewhat academic. Most Surveys even today just use a record basis of bearings which is really sad given how easy it is to get a better B of B. I don't see what is wrong with a statement as simple as "Basis of bearings is geodetic north as derived from GPS observations at (a point described)." I have seen a lot of old surveys, particularly in rural areas, that state "Basis of bearings is true north based on solar observations at (a point described)." They didn't show all of their field notes and calculations on the Survey; you just take their word for it. It's amazing how close they usually are to my determination from GPS.

I don't see what the harm would be if someone published supplemental information on a R/S which, for example, could be a coordinate on one of the monuments on it. I would be ecstatic a lot of the time if I only had a position from an OPUS solution and the geodetic bearing of one line even if the Survey is drafted in another Basis of Bearings. It would be understood that this position is provided as a convenience and may not meet a particular standard.

On the other hand, if someone is publishing new control monuments on a Record of Survey which has the primary purpose of establishing a control monument or monuments then yes they should go the distance.

[Jason Gasser]

Dave, thanks for starting this thread. After reading the PRC and this thread, I remain unclear whether grid bearings alone will trigger all the PRC requirements. It seems to me that the spirit and INTENT of this law applies to those maps/plats that are using northing-easting coordinate values, with a stated accuracy, as a means to show survey mark positions. To the best of my understanding, the PRC does not address the use of grid/geodetic Basis Of Bearings in the absence of coordinates. It only includes the use of coordinates and values. I interpret “valuesâ€￾ to be northings & eastings, while many others interpret “valuesâ€￾ to be northings, eastings AND bearings, or other data based on state plane coordinates. I very much agree that the local monuments in the ground control the survey and its retracability, regardless of how the map/plat is said to be oriented. Unfortunately, the PRC isn’t clear on this point of using bearings only, and many have an all-or-nothing interpretation - meaning any GPS/geodetic information (including grid bearings) shown on the plat triggers all the requirements for reporting methodology, equipment, software, accuracy, residuals, etc. I do not take the view that grid bearings alone rise to the intent of the code and subsequently trigger all the other requirements, however, I would be grateful for further insight about the INTENT of the PRC authors and their use of “valueâ€￾ in the code. Thanks in advance.