Nate The Surveyor, post: 365136, member: 291 wrote: O dang. I'm in trouble.
Confession time.
I have used BLM plats wrong for a long time. Without realizing what convergences were. And, that each line was on it's own little system. (Really now, who draws plats, with MULTIPLE DATUMS, and does not warn the user!)
Well, the BLM does. User is not supposed to be un educated! (ha!)
So, long and short, Loyal is right.And, I am working to get up to speed on this.
One complaint I do have though, is that There is NOBODY doing this for all the 30+ years of Continuing Education.
I recognize the need for me to "get fluent" with this. And, I see alot of others "abusing" the system, ie, just like me.
N
Nate you've been taking the wrong continuing Ed;-)
Alot of the BLM plats around here, are from the 1930's, and do not close by 3', 5', even one did not close by 29 feet.
So, I guess it was MOOT, on some of those!
N
Nate, I wouldn't say you have been using the BLM plats incorrectly.
Unless you are retracing a township line, you really don't need to worry about convergence.
It drops 2" on the midpoint of a section line at my latitude.
If someone complains about that 2", well.................
Nate The Surveyor, post: 365140, member: 291 wrote: Alot of the BLM plats around here, are from the 1930's, and do not close by 3', 5', even one did not close by 29 feet.
So, I guess it was MOOT, on some of those!N
Remember, those are field measurments and they have allowable closure, they aren't supposed to close perfectly.....
And you need to calculate them true north.
What this does to my brain....
Is when entering a local BLM plat, into a computer....
I can manually modify them, via their convergence, to make it all quasi rectangular, (especially 1994 BLM work) and use this mechanism to calc them. I can even do that in my head. And, I can study the USGS quad sheets, and come up with an elevation factor, if there is relief. It is not alot of change, but it bugs me that I did not know.... to do this long ago.
N
Nate The Surveyor, post: 365146, member: 291 wrote: What this does to my brain....
Is when entering a local BLM plat, into a computer....
I can manually modify them, via their convergence, to make it all quasi rectangular, (especially 1994 BLM work) and use this mechanism to calc them. I can even do that in my head. And, I can study the USGS quad sheets, and come up with an elevation factor, if there is relief. It is not alot of change, but it bugs me that I did not know.... to do this long ago.
N
Are you sure that javad doesn't have a routine to calculate true north like Trimble does?
You can do a traverse in true north, you just have to adjust the distances cause it wants an ellipsoid distance.
O shucks, it DOES have that routine in it. Just tell it what kind of bearing you are entering... and it handles it. BUT you have to give it approximate geodetic coords, and a few things. I'm mainly just looking back with regret.
I have come to understand this thing in steps... I asked about being able to enter BLM data into the JAVAD before I bought it.
And, I already see how it works.
It is finally making sense WHY that the BLM did it like this.
N
I just have seen too many surveyors set their GPS on "True north at the base, ground coords" and do this over and over, and ASSUME that the surveys were all on the same datum.
No matter where their base was set.
Nate
Nate The Surveyor, post: 365152, member: 291 wrote: I just have seen too many surveyors set their GPS on "True north at the base, ground coords" and do this over and over, and ASSUME that the surveys were all on the same datum.
No matter where their base was set.
Nate
Well........that's just dumb 🙁
And one of the drawbacks to everyone using GPS
Nate,
The rules and methods of the PLSS are true genius. While execution was far from perfect, I find that errors and fraud are much less rampant than many claim.
It is unfortunate that few LS degree programs go to the depth required to apply the science behind BLM practices. Even worse, I have only had 1 question on all of the exams I have taken that deals with surveying and true north. That's both nationals and three states. One question. Sad.
I commend your willingness to admit what you don't (or didn't) know. I would encourage you to review the Manual while keeping the finer points of 'directions' in mind.
Good luck, Tom
Nate (and others who may have an interest in the subject of this thread) -
;">video by John Balcom of Traverse PC to see some of what he has done with his software to handle the PLSS methods.
John did a presentation at the MARLS conference in Billings back in February. He has created something that is far better than the old CMM (Cadastral Measurement Management) program that BLM used to use.
He has a whole series of videos on associated issues that should give a good overview of what Traverse PC can do now.
GB
MightyMoe, post: 365141, member: 700 wrote: Nate, I wouldn't say you have been using the BLM plats incorrectly.
Unless you are retracing a township line, you really don't need to worry about convergence.
It drops 2" on the midpoint of a section line at my latitude.
If someone complains about that 2", well.................
One common technique here is to apply convergence to precalc a section on grid. I will be looking 50 or 60 feet off if I don't apply it, and that's just line. Across the river the angle is over 2 degrees.