MightyMoe
Yes I know and is why the 2009 Manual has clarified it.
There are also BLMers who don't necessarily believe the east-west centerline is curved and for the most part, they think it is a frivolous argument and not worth the time to debate it.
Just comes down to methods of surveying and my methods (50 years ago) was the same resurveying section lines or subdividing sections. And of course if we were running line with a solar transit, it automatically ran a curved line.
Of course in my day in the field, we were not too concerned with the 0.04' measurements anyway. Didn't have any instrument that measured that close.
But, plenty of surveyors now are arguing about that minute distance and even rejecting monuments like I would have set, because they don't fit the precise measurements or are junior corners bending a senior line.
Unless others think that all of BLM 1/16 sec. cors. have to be exactly, precisely on the retraced senior line?
Keith
Major Issue
Some simply do not concern themselves with curved lines, therefore they do not exist.
Keith
adam
Would you guys agree that back several years ago, when I first posted about curved lines, most of the posters went berserk at the thought of it and I was some sort of lunatic for even believing such a radical idea.
Well now, quite a few years later, some still don't get the fact that we live on a round surface and simply will not consider the fact that some lines are curved.
So, is this not more interesting then some threads on here?
Keith
MightyMoe
Of course in my day in the field, we were not too concerned with the 0.04' measurements anyway. Didn't have any instrument that measured that close.
Keith; I'm still not concerned with it!;-)
Curved v. Straight
Curved v. “straight.”
Although this appears to be a point of “technical minutia” to many folks, I think it is a non-trivial matter for the following reasons:
1. In many PLSS States, the BLM Manual of Instructions has been codified into the State Statutes (to some extent or another).
2. There is an INSANE(IMO) predisposition among Land Surveyors to RETURN Bearings and Distances (around a Section) to Hundredths of a foot, and arc-SECONDS of Bearing (and of course coordinates to hundredths or even thousandths of a foot).
3. The AVERAGE Land Surveyor's office today, contains more COMPUTER capability than all of NASA had only a few short years ago, so there really isn't any excuse to to NOT do the proper calculations.
Now whether you chose to RETURN “True Bearings” or “Grid Bearings” is irrelevant (to me), just tell me what they are. But IF you insist on returning bearings & distances to hundredths and arc-seconds, then for heavens sakes pay attention to the DIFFERENCE! If ALL of your distances at expressed at an elevation of [say] 5,000 feet, then say so. If they are expressed at the mean-elevation of each individual line, then say THAT. If you DON'T KNOW, then say you don't know, that way I won't expect any more than I should!
IF you are in fact doing 1:5,000 (or even 1:10,000) work, then it (curved v. straight) really DOESN'T MATTER much, but DON'T dump that data into an LSA program, and then return the results on your plat at the nanometer level (remember significant digits).
When I see distances to hundredths, and bearings in arc-seconds, I EXPECT to hit those monuments at or about the centimeter (call it .04 feet) threshold around a Section. If you MEANT to say +/- half-a-foot, then SAY IT! I will still (in ALL likelyhood) accept your monuments anyway.
Okay, my rant for the day is complete, time to prepare for the NGS Webinar this afternoon.
🙂
Loyal
Curved v. Straight
The whole understanding of significant digits is lost in this day and age. You can print out bearings and distances even to the fractional second and the 1/10,000 th foot. It is totally lost.
Loyal, is 100% correct that if you are going to have coordinates printed to .001' or distances to the hundredth of a foot and bearings to the second, with the push of a button.
Back when they multiplied numbers by sines and cosines, and practiced long division and multiplication, they paid attention to when to stop carrying out the mathmatical operation. And when you had to break tape (/chain) and pull distances level up mountains and through trees, you got a good understanding of how accurate everything had to be published....
And I have to agree with Keith, if you are going to call bs on someone else's caps, and not take curvature into account, you aren't all that great of a super-surveyor either. You start calling numbers to some great order of accuracy, you need to know when they curve and what it means.
adam
Kris, I catch your drift. But I just get a kick about whenever someone criticizes the over-discussion of a survey item, and almost never seems to complain about some of the massive beatings-of-dead-horses on the political front. I can almost predict the exact words Mr. Milton or the Gunter Chain are going to state over there...... More power to them, that is what they like to discuss, I just find it funny is all.
Loyal
> Of course, if I find a monument within 2" at either the center of a Section or the 1/4 corner on an east west line I'm too busy celebrating to care.
I'm thrilled to find anything within 2'!!
Loyal
Me too! Even if it's one of my own older ones.
As an aside to accuracy in Sectional surveys. Now that the guys at the local BLM field offices have embraced GPS those new monuments have gotten really accurate.
Curved v. Straight
In California it is pretty universal to survey on a plane in a grid system and return seconds and hundredths and has been for at least 30 years. Obviously 30 years ago a Survey of a section wasn't done to the precision of 0.01' but the map still shows it that way and they usually close mathematically. I realize this isn't completely correct but I don't think I have ever seen a recorded Survey map that accounted for the curved east west lines particularly at the center of section which should be a little bit south of where they calculated it.
Surveyors are largely unaware that BLM Plats are not plane surveys; I didn't know that until Keith explained it. I understand it now.
The computers obviously could easily handle this but most of the commercial Cogo software is setup to be used to do traditional plane calculations. If I monumented the center of section a little bit south and filed the Record of Survey I'm sure that would take a little explaining to the County Surveyor. Most of the time the monument is already there, of course, but not always.
I get Keith's and Loyal's point but I don't know what the answer is when the issue is mostly ignored by Surveyors unaware of the curved east-west lines.
Curved v. Straight
I get Keith's and Loyal's point but I don't know what the answer is when the issue is mostly ignored by Surveyors unaware of the curved east-west lines.
I've for years been toying with the idea of submitting a plat to the county or city with true north bearings. It might be fun to watch what happens during the review process.
Curved v. Straight
I hope they don't charge by the hour for map checking because you are going to pay them a lot for their education! 😉
It might take 8 hours to explain to the County Surveyor why your center of section is 0.08' south of the grid intersection. First you have to get him to listen to you; that could take 4 hours of sermonizing out of the Manual. The first requirement for education is the student needs to accept what is being taught. Keith initially pointed out east-west lines are curved and hardly anyone believed him even though he was right. You also see this principle at work when Stahl writes a long explanation of a piece of boundary law and the very next poster writes a single sentence sort of like "I was always taught blah blah blah the opposite of what Stahl just explained." It's hard to accept that maybe you were taught wrong. We in the training professions (flight instructor) call that primacy, "That which is taught first sticks the best" so you better get it right the first time.
A Surveyor I know asked me why he couldn't get a BLM Plat to close and I explained that it isn't in terms of grid bearings, every bearing is true. He didn't know that and I admit I didn't know that until recently.
Curved v. Straight
A Surveyor I know asked me why he couldn't get a BLM Plat to close
And they return what they actually measure along each line? It's not adjusted?;-)
Curved v. Straight
I don't know about today but in the 19th Century they didn't adjust their Surveys (I don't think).
We have Rancho Plats that mis-close by hundreds of feet. The Plat is just a picture of their actual measurements.
Curved v. Straight
I believe right now (I'm not sure, you'd have to ask one of them) they are using coordinates to position the corners. I do know they do have coordinates on all the monuments.
Then I assume the bearings and distances are inversed numbers. This would of course result in a plat that closes-if you correctly calculate it using true north bearings.
Curved v. Straight
I am not sure about all the field survey practices now days in BLM, but in my day in the field, I returned the bearings and distances as determined in the field and were never adjusted. One can easily determine this by running a closure of one of my resurvey plats and of course add convergency into the closure.
Probably the main reason that I bring up curved lines all the time, like I am accused of, is the fact that surveyors argue about being able to measure distances the width of my finger nail and cannot grasp the concept that we live on a round surface.
I hope I have enlightened many to that fact and maybe take the dusty Survey Manual off the shelf and study it, rather than the machine manual.
Kind of a simply concept!
And thanks to Loyal for putting this in language that present day surveyors understand.
Keith
Dave
Maybe the point of all this discussion is to make a few more surveyors think about what they are actually measuring and then what to do with those precise measurements!
Whenever I see a picture on here of a pin cushion monument that is a couple of tenths away from a prominent monument; it is clear that some only use measurements for their judgement in where the "true" corner is.
With more threads like these, maybe they will get a clue!
Keith
Keith
I calc'd it. Next time I set a center of section by intersection I'm offseting it 0.13' north from a tangent run 90° right from the west line of the Section ;-).
Curved v. Straight
I am not sure about all the field survey practices now days in BLM, but in my day in the field, I returned the bearings and distances as determined in the field and were never adjusted.
No LSA program? Heavens!;-)
Dave
Something like that!
