Basis of Bearings

[JoeC]

A topic that I think is very misunderstood.

I see many different ways surveyors and engineering us this on their maps and there is no consistency.

Why I ask is because I see the use of a basis of bearings on – centerlines of roads (with no monument ties), the use of two new monuments set on a record line as a BOB, and often one monument on a record line with a set monument or no monument on that same line as the BOB.

The way I understand it is there must be two found record monuments or there must be a note on the basis of bearings stating using of a geodetic or solar observation as the BOB.

Question is what is the requirement for the basis of bearings on record maps? And per what reference?

[Greg Ippolito]

In the absence of controlling monuments the road itself could be considered a monument. I have seen many maps where a centerline was established by curb split and used for a BOB. It is helpful for future surveyors if the centerline is then monumented so the boundary and centerline are retraceable. Sometimes occupation and improvements may be all you have to go off.

[LS_8750]

What's cool is when you tie out a few monuments a mile apart from a 50 year old map based off solar observation and your GPS finds them out by less than a minute. Hat tip to the old guys!

[pls7809]

This publication has some good info about B.O.B.'s. This is from the OC Surveyor website, but was prepared by the County Engineer's Association of California (CEAC).

For subdivisions, the local agencies can require that certain control be held, depending what is called for in the local subdivision ordinances. Like Orange County requires ties to their OCS Control stations for subdivision maps.

RS's are not local products and are not legislated by local laws. They can be tied to record map bearings, NGS Control Stations, CORS, the sun, etc.

Forgot the link:

http://www.ocgeomatics.com/Home/pdf/Cor ... e-2009.pdf

[E_Page]

As long as it's retraceable, there's a lot of leeway as to what a surveyor can use and indicate as the BoB.

[Ian Wilson]

The only addition I would make, Ken, is concerning your description of your procedure for establishing geodetic bearings through use of GPS survey equipment.

Per the California PRC (§8875), the survey shall meet all of the following requirements:

(a) The survey shall be referenced to and shall have field-observed statistically independent connections to one or more appropriate reference stations that is one of the following:
(1) CSRN station.
(2) Geodetic control station located outside of the State of California that meets all the requirements for inclusion in the CSRN except that the station is outside California.
(3) Existing CGC83 station that:
(A) Is shown on a map filed with the applicable county surveyor by a public officer, subdivision map, corner record, or record of survey.
(B) Meets all the requirements for inclusion in the CSRN except that the station and its data are not published by NGS or CSRC.
(C) Has an accuracy, conforming to the applicable CSRN requirements, stated for the station's value.
(4) Existing CGC83 station that is shown on a public map or document that:
(A) Is compiled and maintained by the applicable county surveyor.
(B) Meets all the requirements for inclusion in the CSRN except that the station and its data are not published by NGS or CSRC.
(C) Has an accuracy, conforming to the applicable CSRN requirements, stated for the station's value.
(b) If an accuracy is to be claimed for the CGC83 value or values established, the claimed accuracy shall be an accuracy standard published by FGDC or FGCS.

You’ll also need to show your control scheme, including the coordinates used for the reference stations from which you derived the bearing. That means you’ll have to comply with §8877, as well.

When a CGC83 value or values are shown on any document, the document shall include the following:
(a) A statement that the geodetic coordinate value or values shown are a CGC83 value or values; exceptions shall be noted.
(b) The station or stations to which the CGC83 value or values are referenced and connected and the geodetic coordinate value or values and the published or stated accuracy or accuracies of said reference station or stations.
(c) The epoch of the CGC83 value or values shown. The epoch shall conform to provisions of subdivision (b) of Section 8876.

And, of course, §8876 rears it’s head:

If an accuracy is claimed for a CGC83 value or values, the survey that established the value or values shall be documented on a map, record of survey, corner record, or other document that includes, at a minimum, the following:
(a) For each CGC83 station, the resultant CGC83 value or values.
(b) The epoch (date), in a decimal year format to two decimal places, that is the basis of the CGC83 values shown. The epoch shall be the published NGS or CSRC epoch of a controlling station for the survey.
If the published epochs for the horizontal positions of the controlling stations are not the same, appropriate adjustments shall be made to the horizontal values of the controlling stations so that said values of all the controlling stations are at one consistent epoch published by NGS or CSRC. These adjustments in the coordinates of the controlling stations shall be made in accordance with procedures and values published by NGS or CSRC.
(c) The FGDC and FGCS accuracy standard of the CGC83 value or values established. FGDC accuracies shall be identified as either a local or network accuracy.
(d) Additional written data that justifies the FGDC or FGCS accuracy standard shown. Such additional written data shall include observation equipment, control diagram including required field-observed statistically independent connection or connections, adjustment methodology and software used, a summary of the procedures used or a reference to published commonly accepted procedural specifications, final residuals or closures, and other data essential for others to evaluate the survey.


In short, contrary to popular opinion, it’s not as simple as set ‘em up and fly. There are a number of additional requirements to consider before using a geodetic basis of bearings derived from GPS observations. Failure to comply with them means that you are not keeping with the requirements of California statutes.

[btaylor]

I think the BoB issue in general is massively overrated when it comes to an ROS. I am more interested in the ROS propagating the monuments properly so I can retrace things.

Take a block determined by split of improvements with monuments set at a lot corner in the middle of the block, and nothing else noted as set on the map. I cannot set up and tie to two front lot corners and get on the same block calcs unless I measured those perfectly and they were set perfectly. I then have to also measure all the improvements and check those monuments.

I prefer people get anal about things that have an impact on the "retraceability" of the map rather than if the curb splits on one street were held as being a bearing from a 100 year old map. The BoB is almost irrelevant on most ROS maps I deal with. In fact, whenever I work in San Francisco I am not sure if I see bearings. Every line shown is 90 degrees, and there is always a note to this effect.

[Jim Frame]

"Question is what is the requirement for the basis of bearings on record maps? And per what reference?"

I don't know of a specific reference. Absent one, it's left to the professional judgment of the land surveyor and the constraints of the standard of practice.

I don't see any problem referencing CCS83 as established by GPS observations on a monumented line for the basis of bearings. As I understand it, the PRC only comes into play if you publish coordinates for one or more points on your survey.

Most surveys are of sufficiently limited extent that even an autonomous position (I believe the term in Trimblese is "Here") is close enough to get you on the grid within the noise level of the typical boundary survey, although with the advent of OPUS it's trivial to get a whole lot closer than that.

.

[Lee Hixson]

I'm in the camp that the B.O.B. is not that important. (McComb makes a valid point, but it's a minor one.) The B.O.B.s importance comes into play, 1) if you are obtaining your bearings from a previous map, and 2) later on, in the analysis stages, when you are comparing bearings, looking for any busts or irregularities.

As long as another surveyor can "get on" my bearings without a great deal of trouble, that's all that matters, really. Of far more importance is that my map data confirms the field positions of the monuments I show--they are in agreement. That forms the foundation of the entire map, whereas the B.O.B. is trivial in comparison.

The most important thing is, of course, the resolution process: by what line of reasoning did you make the decisions and choices that are memorialized on your map? The B.O.B. is a minor step at the beginning of the process.

[Gromatici]

The method you're describing is simply ground distances, no datum. The program gets the mapping angle from the coordinates it calculates from the autonomous position it calculates when you set up you're base (Trimble works the same way). You could simply put a note on your map that you derived True North based on static GPS observations and use the mapping angle of ___________ at Lat. Long. as derived autonomously. That might even be more confusing!

Anyway, I've used that method and it works great for getting on a Baseline when you only have one mound of stones and you're looking for one up the hill a mile.

The logic in my mind that you can use is you are determining "True"
North based on GPS constellations, much like older maps make a note that they used a Sun shot or Polaris. Seems like it should be simple, but maybe adding some information like the mapping angle and Lat. Long. of the autonomous position you used would help the surveyor down the road re-create the survey if he can only find one point?

I wonder if THAT would trigger the requirements in the Public Resources Code regarding the data needed when showing SPC? If it does, go with plan B.

I remember taking a course while Paul Cuomo was alive and a lady who had already sat for the State Exam was wondering where they get the bearings from on Record of Surveys. Paul was always nice to the ladies. A true gentlemen. I was laughing to myself because I know that he would have been a little harder on one of the boys! He was a great guy! Anyway, it's good to go over this stuff because you'd be suprised how many people just put thier heads down and work and never think of it.

Which county have you been having trouble? I'm curious because, as a matter of local culture (or so it seems), many surveys in the City Blocks of Santa Barbara will say "assumed bearing of N41-30E along " as the Basis of Bearings. That's because ALL the street are "supposed" to have N41-30E or N48-30W on the streets as laid out by Haley and then affirmed by the City Council. You'll see many maps where there isn't even a monument at the Basis of Bearings line. Anyway, it seems like there always an exception to the rule.

[btaylor]

Boy Ken I cannot think of too many new subdivisions in Menlo Park. I am thinking this must be the Vintage Oaks subdivision?

[btaylor]

Wow Steve that is....stupid.

[dmi]

Steve, that is a prime example of the application of a rule to the exclusion of common sense. So what once was a B.O.B. is now a B.O.O.B.

[btaylor]

Oh. I was close. It is the same surveyor. Partial credit.

[PLS7393]

And why haven't either of you (Ken or Bryan) contacted the Board on this surveyor that is filing a Subdivison Map and not completing his professional duties as a land surveyor by setting monumnents.

I don't care of the city has released the bonds, that surveyor is still responsible. Send him a letter inquiring, and cc the City of Menlo Park and the State Board. I garauntee something will be done, especially since the map was filed such a long time ago, oops it was only 12 years ago in 1998.

[PLS7393]

One more thing pertaining B.O.B.

I have spent a number of hours researching this in the past and the CEAC definition is the only one I have found. No text book or reference I own has a definition.

I do agree with the CEAC definition too.
In San Mateo County, where a number of old maps did not set monuments, and there is no monument preservation fund, so street monuments are far and few apart, I have established some standards too.

If a surveyor ties out a number of found property corners (record and un-recorded monuments) and states the basis of bearings is the "Northerly right of way line of A Street" when the northerly line is not monumented, I request they add a statement at the end of their basis of bearings. I have them include "AS ESTABLISHED FROM FOUND POINTS SHOWN HEREON".

I believe it is safe to say that we all understand they used the found points and performed a best fit situation. As the map is a record of survey, of that surveyor, this clarifies how he got his orientation.

[btaylor]

"And why haven't either of you (Ken or Bryan) contacted the Board on this surveyor that is filing a Subdivison Map and not completing his professional duties as a land surveyor by setting monumnents."

Keith speaking for myself, I am unaware of this and only inquired where this was. I have not surveyed that subdivision.

EDIT - I see the confusion. I only referred to another subdivision that I was involved with, but I am pretty sure that one is monumented fine. The one Ken is referring to is the only one I am aware of.

On this issue however, I would first contact the surveyor and not the Board. I do not see the need to contact the Board if one can contact the surveyor first and give them a chance to rectify the situation.

[PLS7393]

Ken,
Unfortunately most agencies do not get the surveying authority involved before the bonds get released. That is due to most agencies use the planning department to control the project, which works if they get a punchlist item for survey monuments with all subdivisions.

Once monuments get set, then they can be used as a Basis of Bearings (to keep this on the original topic of B.O.B.)