Bearing Basis for Profit
> By any familiar standard, they were less correct. :>
That was a long post to say that you agreed with me.
In 100 years, or 10 or whatever, your method of finding and defining North will be superseded by another, better method.
What will matter is are the monuments on the ground. It is nice, even useful to define those monument's positions to a national geodetic datum. This is useful for perpetuating the monuments.
Tying it to true north, is elegant. The actual usefulness is small, which is demonstrated by the necessity to define what you even mean by North. (There is more than one direction called North.)
I believe the most reliable way to perpetuate monuments would be to publish vectors from the closest two or three NGS CORS stations. Assuming they are close, and on the same Teutonic plate, that would seem as permanent and useful as possible.
Bearing Basis for Profit
> That was a long post to say that you agreed with me.
Obviously, I think you're quite misguided if you actually believe the following that you posted:
> Tying it to true north, is elegant. The actual usefulness is small, which is demonstrated by the necessity to define what you even mean by North.
By your logic, presumably using standard units of distance measurement is of no use since a surveyor would have to say whether they were US Survey Feet, International Feet, Meters, Yards, Rods, or Chains. That doesn't make any sense as an objection, either.
> So, where did the plat "North" about 2°41' to 2°43' off true North come from? Beats me, but it sure looks like RTK GPS has struck again.
I don't share the same appreciation for GPS measurements as others that frequent this forum do, but is it grounded in reality to think RTK GPS was used to stake a subdivision in 1998? Isn't it probably more likely that the block of lots that you were retracing were staked off a conventional traverse, where the fronts of the lots were set, probably coming from one direction, and the backs of the same lots were set from a separately, but connected, traverse line coming from the opposite direction? In other words, the side lines of the lots weren't actually measured by occupying the lot corners and turning the calculated angles and setting the opposing lot corners.
If the scenario I envision is the case, having the entire subdivision on a *repeatable* basis of bearings, while a beneficial thing, would still have left you possibly placing the corners 0.20' out of their original position, if all you had left to rely upon were the bearings of the platted lines.
Bearing Basis for Profit
> I believe the most reliable way to perpetuate monuments would be to publish vectors from the closest two or three NGS CORS stations. Assuming they are close, and on the same Teutonic plate, that would seem as permanent and useful as possible.
You mean that it is most reliable while the same Continuously Operating Reference Stations are operating, I take it. Not sure about its permanency. I kind of think a reference to a celestial body has a little better test of time.
I think you're right Alan. We've been doing subdivisions for a while of varying sizes. One thing I learned early on was that the initial survey around the perimeter of a tract for subdividing needs to be done as precisely as possible, because ultimately, as you work the layout from the inside out and the outside in, the perimeter error in your whole tract is going to show up in a single 70x125 foot lot. Looks like something to that effect was the case in Kent's subdivision.
I will say that RTK properly done will provide bearings as close as any other commonly applied method.
Bearing Basis for Profit
> In 100 years, or 10 or whatever, your method of finding and defining North will be superseded by another, better method.
>
I have no doubt that "North" will only become more easy to determine in the future and perhaps with ever increasing precision, but that's an asinine argument against determining reproducable bearings today. Those future surveyors, employing "better methods", will be able to use my antiquated bearings with some benefit. They won't be able to use those assumed bearings for much of anything.
> I don't share the same appreciation for GPS measurements as others that frequent this forum do, but is it grounded in reality to think RTK GPS was used to stake a subdivision in 1998?
I suppose I could ask, but there were many surveying firms in Central Texas using RTK GPS in 1998. I agree that it's fairly unlikely that the individual lot corners were set via RTK. The relative accuracies are too good for RTK, i.e. three markers actually being on as good a line as can be laid out with a total station without the random noise that is typical of RTK stakeout.
>Isn't it probably more likely that the block of lots that you were retracing were staked off a conventional traverse, where the fronts of the lots were set, probably coming from one direction, and the backs of the same lots were set from a separately, but connected, traverse line coming from the opposite direction?
That is also a possibility. I was thinking RTK because the whole layout has a larger scale error than I'd expect to see in conventional work, about 1:6,000.
> If the scenario I envision is the case, having the entire subdivision on a *repeatable* basis of bearings, while a beneficial thing, would still have left you possibly placing the corners 0.20' out of their original position, if all you had left to rely upon were the bearings of the platted lines.
Obviously, having a repeatable bearing basis requires that the subdivision is at least surveyed to a minimum standard. Naturally, by "repeatable" bearing basis, we mean actually being able to re-establish the directions of lines by independent means such as astronomic or GPS methods. If the whole work is shot full of large random errors, that pretty much shoots any bearing basis down, independent or not. There is none.
> Obviously, having a repeatable bearing basis requires that the subdivision is at least surveyed to a minimum standard. Naturally, by "repeatable" bearing basis, we mean actually being able to re-establish the directions of lines by independent means such as astronomic or GPS methods. If the whole work is shot full of large random errors, that pretty much shoots any bearing basis down, independent or not. There is none.
I couldn't agree more in that having a repeatable basis of bearings, such as GPS or astro observations, would be most beneficial in those times where the big yellow monsters, rogue fence builders, or haphazard utility crews have displaced the original monuments from their original locations. The main caveat I see to reliance upon those bearings is that it's highly unlikely all lines were independently observed. So what you're left with is finding at least two original monuments with a degree of certainty that those monuments are in their original positions, calculating an astro-observed bearing between them or GPS observed vectors, rotating the entire subdivision to your calculated bearings, and then hoping for the best.
Naturally, my opinions revolve around the notion that we're still referring to the above cited project of your's.
Kent
> > So..what is the issue? Did the original plat state it was on true north? Are you required to have your surveys based on a recoverable bearing basis?
>
> Yes, Texas practice requires some statement as to the basis of bearings and that they refer to something other than the sparkle of sunlight on a pond. In the 19th century, the bearing basis of a survey run in that area would have differed by about 1 degree counterclockwise from true. One value of variation that was used for years was wrong by about that amount. So, it's striking that in the modern era when GPS is widely used and solar observations are a snap to reduce, that bearings would be so far from any independently reproducible value and in greater error in an absolute sense than most of the 19th century surveyors reported.
Are you saying that the subdivision plat didn't have a basis of bearing statement, or that you feel that the basis of bearing should be only grid? If it's the first, then I have to agree with you somewhat, but if it's the latter, that's imposing one's will on another, when the board very specifically doesn't require it, regardless of whether a county needs a digital copy......
Well said Alan.
Kent
> Are you saying that the subdivision plat didn't have a basis of bearing statement, or that you feel that the basis of bearing should be only grid?
Neither. Astronomic or geodetic North is also an independently reproducible basis for expressing bearings (as long as the meridian of longitude where that North was determined is stated.)
> I couldn't agree more in that having a repeatable basis of bearings, such as GPS or astro observations, would be most beneficial in those times where the big yellow monsters, rogue fence builders, or haphazard utility crews have displaced the original monuments from their original locations. The main caveat I see to reliance upon those bearings is that it's highly unlikely all lines were independently observed.
Except it's highly likely that the TBPLS minimum standards will remain in force for the indefinite future. So, while it may be prudent to ask whether a survey was competently made, the presumption at least is that it was.
> So what you're left with is finding at least two original monuments with a degree of certainty that those monuments are in their original positions, calculating an astro-observed bearing between them or GPS observed vectors, rotating the entire subdivision to your calculated bearings, and then hoping for the best.
No, in this case the exercise is one of correctly reporting the actual bearings of the lot boundaries in relation to a North direction that any competent surveyor should have no difficult determining at any time in the future. The skew of about 0°02' in the shape of the lot means that the subdivision itself has no bearing basis more accurate than +/-0°02' and determining the bearing of any one line can't be likely more accurately extrapolated to any other line.
