Due North in PLSS Retracement

Astronomic or Geodetic North will work just dandy.

The "original" surveys were astro, but the LaPlace Correction is generally a trival matter in most cases.

Loyal

The PLSS uses astronomical North, but yeah, most of the time geodetic will work fine for a proportion. If you are going a long distance I'd check what the difference is though. The BLM surveyors in Alaska used a gyroscope or an astronomical reading.

You can use GPS, just make sure you're not using grid north.:-)

Jeff,
Out here in PLSS heaven, retracement is quite common practice. In retracing original surveys or even a BLM retracement survey, the bearings are referenced to the true meridian (astronomical). The true meridian is a line along the meridian of longitude. Historically, determination of the true meridian has been based upon direct astronomic observation at the point of record and, thus, an astronomic meridian. Dealing with GPS these days there is a slight difference between the astronomic meridian and the geodetic meridian at a given point. The difference is referred to as the Laplace correction and is a result of the difference in direction of the local gravity vector, the normal to the goeid, and the normal to the reference ellipsoid. The historical practice of using an astronomic meridian versus the current capability to get a geodetic value can create a potential ambiguity that must be resolved in only special certain cases. The basic accuracies required in most surveys make the Laplace correction inconsequential. For us old non button pushing surveyors, it's just common practice to know where true north is in our surveys. The proportionate offsets in double proportions are always due East or West. One other item, the original surveyor through his methods or procedures prescribed by the Manual of Instructions, reported his bearings in reference to the true meridian. In the retracement process many times you can find that the original surveyor was actually running east or west by a certain angular difference from the true meridian and can be used as a "index correction" to look for the monument at your next search point. Hope this helps.

Pablo

Thanks for the responses.

I agree that the original surveyor was instructed (via the manual in force at the time)to run and reference lines to the true meridian.

However, for one reason or another, the guy doing the survey 150 years ago might not have been able to ascertain the true meridian as accurately as we can today. So, in attempting to retrace the original surveyor's work and restore lost corners, wouldn't we get closer to the original monument location by using the same "cardinal directions" that the original surveyor held (error and all)? Pablo mentioned applying an index correction to search for monuments. To me, it makes sense to apply an index correction to the cardinal offsets when restoring lost corners via double proportion. Or, hold the bearing of one line on the govt plat as your basis of bearing, thus tying into the original surveyor's meridian reference. Am I out in left field on this one?
Forgive me if I'm missing some of the basic concepts here. I'm mainly a construction surveyor trying to learn the nuances of land surveying. Thanks again for the help!

Jeff

Have you looked (can you find?) the original notes to deduce if the line was run
by 1) solar compass, giving a precision of about 5 arc minutes, and corresponding accuracy if things were in good adjustment,

or 2) by magnetic compass using a solar or Polaris reading to find the "variation" (declination) at the start of the line, in which case there could be a loss of accuracy in transferring between instruments, or a change in declination of a few minutes during the day on top of the astronomical accuracy,

or 3) by magnetic compass using a variation determined somewhere "nearby" by him or someone else, in which case there would be both time and distance changes in the declination, further reducing the accuracy and I wouldn't expect to it to be better than 10 minutes unless there was luck.

"the guy doing the survey 150 years ago might not have been able to ascertain the true meridian as accurately as we can today."

In most cases true. That is why original lines and monuments run hold over measurements (distance and/or bearing).

"So, in attempting to retrace the original surveyor's work and restore lost corners, wouldn't we get closer to the original monument location by using the same "cardinal directions" that the original surveyor held (error and all)?"

Yes, but can you really recreate the same cardinal direction? I would say most of the times no. Again, that is why the evidence of the original lines run trump measurements. The only way to get on the same cardinal direction and chain length correction is to have two origianl monuments to "check". But if you have the monuments, why would you need the obtained "corrections"?

"To me, it makes sense to apply an index correction to the cardinal offsets when restoring lost corners via double proportion."

The use of proportion in most instances and when properly used, automatically apply any needed "index correction".

"Or, hold the bearing of one line on the govt plat as your basis of bearing, thus tying into the original surveyor's meridian reference."

Be sure you truly understand the difference between a grid north (localized and SPC) and the true meridian. They are not the same. In other words, in a localized grid projection, the east and west lines of a section are parallel, but when both lines are referenced to the true meridian, they are not parallel.

All good questions. I suggest reading and rereading the pertainent sections of the 2009 BLM Manual.

If I recall correctly, the section lines were instructed to be parrallel with the east line of the Township, rather than due north or meridianal. In addition, the use of a magnetic compass was authorized for layout of those lines per that instruction into the early 20th century. As you say, it could have been done in any number of ways in the original survey. Those more familiar with the system have mentioned that many of these lines were run astro north with a solar compass. So I get your question, but I think the instructions for double proportion do call for due north. That would be as good an instruction as any.

The problem with where you are going with this is that the monuments found and used for the double proportion do not necessarily (maybe never) constitute parrallel lines with the other sides. So, which sides do you use? Better to just use cardinal directions.

One way to look at it is that the double proportion is not a retracement at all. Rather, it is an equitable solution designed to place an original monument when all evidence of the true original location is gone. In this scenario slight differences in direction have little relevance. You are merely dividing up the available land in the fairest manner and for the first time. So whatever you decide, the rest of us should honor it, if it is reasonable.

I was once told by a CEU provider that surveyors on the east coast
typically do better than PLSS surveyors when it comes to PLSS questions.
Duane is correct in his first two statements.

Ben Buckner told us surveyors attending a seminar that due north for
a certain section was connecting a point south of the lost corner and
a point north of the lost corner. Due east was connecting a point west
of the lost corner to a point east of the lost corner.

Following the footsteps of the original surveyor means retracing between
original monuments, not looking in the sky for a solution. In the original
survey was done with a compass and a chain, then GPS will give you a precise
result but not necessarily an accurate result when relocating the original
position. Also, retracing the original surveyors' footsteps would mean
using an 1800's manual not the 1973 manual.

A guy named Martin from Washington state did a bunch of research on
this subject and came to the conclusion the resulting 1973 manual solution
did not give a proportion result especially when the lines on the ground
varied greatly from cardinal directions. Double proportion is a mathematic
solution; it cannot be redefined by surveyors or government agencies.

http://www.blm.gov/pgdata/etc/medialib/blm/ak/aktest/cadastral.Par.86851.File.dat/lost_oblit.pdf

Here is excerpt from that document:

"By double proportionate measurement, the lost corner is reestablished on the basis
of measurement only, disregarding the record directions."

Direction or bearings mean nothing in double proportion. You proportion along
each of the lines and then intersect perpendiculars.

Cardinal Equivalent

Jeff,
Take a look at cardinal equivalents as explained in the manual 2009 and using double proprtionate measurement. i.e. Sections 7-8 and 7-9. i.e. "Failure to determine the direction of each line with reference to the true meridian (cardinal) could produce erroneous results".

Pablo

Duane, the section lines were to be run parallel with the east boundary, but that boundary was not necessarily due North. If it was within 21 minutes of due North, it was ok and the interior lines were run parallel which meant that every north-south line was run about a minute (depending on latitude) westerly from that original bearing. See the sample plat in the Manual.

That minute difference made them parallel.

Keith

http://www.cadastral.com/papdpxb.htm
The above is a link to a paper by Jerry Wahl on double proportioning that may address some of your questions. It's been around for awhile so you may have ssen it before.
DJJ

I believe the theory behind using cardinal directions and not applying an “index correction" is that on departing each newly established section corner an independent azimuth determination was often made. From an interior section corner it is possible that each of the four section lines used separate azimuth determinations determined at three different points. Unlike most surveys we perform the BLM/GLO surveyors did not use one basis of bearing for their whole project. They were not turning angles throughout the township. The only situation in which I would apply an azimuth correction is if I had surveyed a large portion of a township and found a consistent error in the bearings.

> Here is excerpt from that document:
>
> "By double proportionate measurement, the lost corner is reestablished on the basis
> of measurement only, disregarding the record directions."
>
> Direction or bearings mean nothing in double proportion. You proportion along
> each of the lines and then intersect perpendiculars.

And another....

> "In all cases where no public lands are involved, the surveying procedure must
> necessarily be brought into harmony with the State law and court opinion. In such > cases,
> the methods and explanations of the Bureau of Land Management must be regarded as
> advisory only, as that Bureau is without jurisdiction unless Federal lands are > involved."

😉

Radar

The Bottom Line

The fact is:

If you proportion in an original corner you WILL NOT be placing it back in it's original position.

So don't do it......

Radar

Radar

"In all cases where no public lands are involved, the surveying procedure must
necessarily be brought into harmony with the State law and court opinion. In such cases, the methods and explanations of the Bureau of Land Management must be regarded as advisory only, as that Bureau is without jurisdiction unless Federal lands are involved."

Yup...but how many "land" surveyors can even answer that question (are there any Federal Interest Lands INVOLVED)????

It's been so long since I worked in a Township that did NOT contain Federal Interest Lands, that I'm not even sure that I ever HAVE!

Loyal

Loyal

a Township that did NOT contain Federal Interest Lands

Is there such a thing?

Mighty

I dunno...I'm sure there are (somewhere back East I suppose), but not in my neck of the woods. There might (MIGHT) be one or two around Salt Lake City and maybe (MAYBE) around Odgen, but that's about the only places this side of Denver that I can think of off hand. Oh I'm sure CalifornIA probably has some, but that's another planet!

🙂
Loyal