Record map note help

different state but, page 4 or 5 of this document might help.

Policy on ties to NCSPCS.

I've been chewing on this recently, myself.

From what I understand, if you mention geodetic or state plane or even GPS, it must be physically tied to a station, either conventionally or with GPS. If you are using a GPS basis of bearings without referencing any stations, would it not just be an assumed basis of bearings?

Brad Luken, LS
_{AZ, CA, NV & OR}

If you are using a GPS basis of bearings without referencing any stations, would it not just be an assumed basis of bearings?

Exactly, it's meaningless without metadata.

You can produce any bearing basis with GPS, so saying GPS bearings doesn't help much more than saying I looked north were I think north is.

If its metadata - maybe a note such as:

"Basis of Bearings:
The bearings (grid) shown hereon are based on GPS observations during the month of _____, 2014.
Observations were processed using NGS OPUS Fast Static protocol. Greater than 90% of the observations were used during processing. Each position was double determined with 24 hours minimum between observations. Grid bearings are NAD 83, Zone ___, in 'State', Epoch 2010."

The map would not have the State Plane coordinates listed. Just the method of how the bearings were measured. Which makes it repeatable for any other surveyor to retrace. Since the values returned by OPUS are SP, isn't this sufficient for a basis?

If it was a Solar or Polaris observation, and so stated, the basis is not assumed. Same with multiple GPS observations.

That would be nice for me if I was retracing you, although, if no coordinate values are listed epoch dates and such become less important.

That is more for coordinate values, OPUS ties will be different than ties to the passive network for the coordinates, but your bearings should be the same, or so close to the same that it's just noise in the values.

So for only bearings telling me that it's the State coordinate system, NAD83, and the zone would be enough. A bearing produced along a line using GPS in 1996 in an NAD83 state coordinate system will match one from 2013.

Also stating your distance adjustment from state plane if there is one is nice to have.

Now if coordinates are produced that ups the need for more metadata, epoch dates, types of survey, static, RTK. How it's computed, OPUS, Adjusted inhouse. CORS or HARN points used and their values at the time of the survey are nice too, and also what elevation control is applied, Bench Marks, or just OPUS and a Geoid model. All that should be included with coordinate values.

Meta-data would include what monuments you tied to, the coordinates you used for those monuments, and how they are tied to physical monuments on your project.

Your note tells us How you did it, but it does not tell us What you did.
I really don't care what software you used (or if you used a pencil and paper) or the implied accuracy the software spits out... we all have to assume the calcs are correct and it is accurate enough for the project.

This is kinda how is is often done, check some record maps for examples...

Basis of Bearings: N72-41-26E (state Grid or Ground) between (Coors station A) and (Coors station B) NAD 83, Zone ___, Epoch 2010. See BoB detail, Sheet 1.

(I think all of that Met-data is spit out by OPUS)

then draft a detail, a simple triangle showing the bearings and distances between the two Coors points and your project, coordinates of the control monuments, grid/ground factor, etc.

this way in the distant future someone can either find your controlling monuments or recreate their positions from historic data, recalculate, and get back to the same locations.

Even a Solar or Polaris observation tells us what TWO monuments/objects you used: one on the ground and either the Sun or Polaris.
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"Basis of Bearings" is rather archaic, what we really want is Basis of Coordinates.

Looked at a CA R/S just the other day which the surveyor stated "basis of bearing by GPS observation taken at the SE corner".

Turns out he was referring to a calcuation from gps observations related to true north.

In my humble opinion, I feel this was a violation of the CA PRC in that it should have triggered the listed provisions in there for reference ties.

In my humble opinion, the CA PRC is in place to ensure that observations which are based on either CGC83 geodetic or plane coordinates, and/or the calculated inverses between those derived values, are properly documented as to the stations for which the values should have been or were referenced to.

Whenever I use gps observations to obtain measurements for a boundary survey, I either:
Rotate those measurements to a prior record and utilize the prior record as a B.O.B.
or
Show those observational reference stations and other CA PRC items for a complete basis of reference to the CGC83 geodetic or plane system.

I personally don't believe taking a GPS vector between 2 observations and claiming the calculated inverse between them as the basis for a B.O.B. is sufficient, and is simply an attempt at circumventing the intent of the CA PRC.

You have discovered the reason for my request ?.

Having seen similar records lately that had a variety of basis descriptions stating the use of GPS. Apparently there is some confusion of the PRC rules. Probably because they did not have coordinates attached. Yet mentioned the GPS basis for the bearings.

The PRC Div. 8 is complicated when coordinates are published (see 8800 to 8818). Has no current provision when GPS is used for bearing basis (see 8813-c).

>Whenever I use gps observations to obtain measurements for a boundary survey, I either:
>Rotate those measurements to a prior record and utilize the prior record as a B.O.B. ...

This is my prefered method due to the complexity of the PRC for publishing coordinates.

Dennis,

I'm assuming you're asking about this from an agency reviewer perspective. Regardless, establishing a direction requires location of the relationship of 2 points. While one may argue the bearing is simply the difference in positional values between those 2 points, it remains that the exact position of each of those 2 points must be first known in order to derive the difference in positional values. An exact position requires coordinates. For the gps user, this means either spherical geodetic coordinates, or coordinates derived from projection onto a state plane system.

The surveyor who claims a B.O.B. based on gps claims a precision of such value when he/she applies the number of significant figures for the bearing claimed as a basis. This display of accuracy of values derived from gps geodetic or gps state plane coordinates triggers the CA PRC. See 8813.3 & 8875.

A B.O.B. from a set of gps observations is a derivation from values created for the 2 points. Without the reference ties to CSRN or equivelant stations, the coordinates of the 2 points utilized for direction have no basis of origin. Hence, no real basis of bearing.

We are talking about a TENTATIVE MAP? This is a map that only will be a record at the planning department and not a true record map. Usually you would rotate the whole to a previously recorded map boundary and that would suffice. I wouldn't get carried away on a TENTATIVE MAP, the GPS notes will belong on the final map, which will be recorded, if the TENTATIVE MAP is approved.

@ clearcut: Starting to see how you are interpreting the meaning of the PRC. Because it requires 2 points to be determined using coordinates, within the CSRC domain, to derive an inversed BOB; then those coordinates must be shown along with all of the metadata called for in the PRC.

Okay I'll buy those requirements. It is for that reason I will use a prior recorded survey bearing for the BOB rather than deal with the PRC requirements. Way too much required data and unnecessary complexity for a BOB.

@ Berk Blake, PLS CA: Yes on the Tentative/Tract. I'm starting one now and was not sure how to interpret the BOB requirements after reading through the PRC, which is incidental to say the least. Saw some other RS's & Tract maps etc and there are different solutions out there. Which just fuzzy up the situation.

Thanks to all that responded. Gained some insights and a decision was made. Thanks again.