Explain "Weak Traverse Angle" Jeff
Did you have any relatively short traverse legs?
RADU
Ahh, the five most evil words in surveying rear their ugly heads again:
"I WAS ALWAYS TAUGHT THAT ....."
Loads of misinformation here. The weak triangles in a traverse with a total station is a myth. Weak triangles only applies to triangulation and resections. It has nothing to do with a traverse with a modern total station. Make those triangles as fat or as skinny as you want, Jeff, my man, 'CAUSE IT DON'T MATTER!
Stephen Calder
It's not the angle and distance you measure, it's what you do with it that counts.
Angles within 30° of 0° and 180° have sines that change very rapidly. A one second difference for an angle near 30° will cause a change in position of 0.004' in 1,000' when calculating that position.
Explain "Weak Traverse Angle" Jeff
Hi Radu,
The lengths of the traverse legs were relatively consistent.
To be honest, for the purpose of the survey at hand, I'm satisfied with the results of the traverse. I'm just having a hard time understanding the weak angle concept as it applies to traversing with a modern total station in general.
Thanks,
Jeff
Hi Dave,
Wouldn't a 1" angular error at 1000' make about half-hundredth difference even if your angle was close to 90deg?
What am I still missing?
At this point I agree with you. However, I feel like I must be missing something if all of the other surveyors on this board have a different opinion. Maybe they can present an argument that will change my mind.
Explain "Weak Traverse Angle" Jeff
I understand what you are saying , I too would have been happy with the closure obtained. But my point on the surveyor's comment on a weak traverse angle was a clarification on length of traverse legs rather than acuteness of the angle.
RADU
This topic deserves a more detailed discussion, because the myth is so prevalent. I don't have enough time this week, though.
Maybe this weekend we could post the coordinates of a 6-corner tract, and ask posters to suggest "good" traverses as well as ones with "weak angles." Then we can analyze the survey designs with a preanalysis program like Star*Net and separate the myth from the truth.
- Doug
we're not building a watch here
sounds like something an office guy would say. Somehow they just can't understand that real world conditions often dictate how we set up our traverses.
Explain "Weak Traverse Angle" Jeff
> ...I'm just having a hard time understanding the weak angle concept as it applies to traversing with a modern total station in general.
Thats because it doesn't.
Peter Lazio
Stephen & Peter
So you're saying it's okay to run a traverse that is 4k' on the South, 300' on the East, 4k' on the North and 300' on the West and the strength of that figure is the same as if it were square?
I'll call BS. The geometry of the parcel is what you have to work with and the above example is crap (we have them all over the place here).
So you come and survey that puppy and tell me that the instrument will overcome the poor strength of figure.
Stephen & Peter
> So you're saying it's okay to run a traverse that is 4k' on the South, 300' on the East, 4k' on the North and 300' on the West and the strength of that figure is the same as if it were square?
>
> I'll call BS. The geometry of the parcel is what you have to work with and the above example is crap (we have them all over the place here).
>
> So you come and survey that puppy and tell me that the instrument will overcome the poor strength of figure.
So Kris you are saying that if you backsite the same point and turn an angle of 15 degrees and go 1000' and then with the same accuracy turn an angle of 90 degrees and go 1000' that the error ellipses of the two points will differ by anything other than the orientation? I call BS. The semi-major and semi-minor axis will be the same for both error ellipses.
Strength of figure is a concept that only comes into play in intersections, whether they be distance / distance, distance / direction or direction / direction.
Peter Lazio
90% Of The Time It Does Not Matter
That the angle is very acute or the BS and FS are way out of balance. When the error occurs there, and you will always have errors, the results could cause a return trip.
It takes minimal time the first time around to observe extra angles or make a redundant oservation.
Don't listen to Ted, if you cannot afford the time to be redundant then you are a "gambler" and not a "surveyor".
Paul in PA
we're not building a watch here
Amen Perry== we hamsha-ites, learned quickly that good geometry makes good traverses, procedures of setting "naturals", back and reverse angles, cross ties, care and dilligence taught to us by many a good surveyor led to good information, then one relied on a good in office surveyor that understood traverses and used weighted input data to balance and adjust for the most reasonable fit--this method proved itself time and time again when tieing into multiple traverses and surveys by others--having spent many years at TFM University in mecca (bedford, N.H.)one learned in quick order the rules of the road in surveying--if you paid attention you could survey with a banjo if need be--the i forgot the gun, or all we have is a broken tape, or the batteries dead were not valid excuses, we had many a trick up our sleeves to "git 'er done---TDD
THATS WHY I'LL PUT A HAMPSA SURVEYOR UP AGAINST ANYONE ANYWHERE ANYTIME--
Peter
No, what I am saying is that you shouldn't create poor geometry for a loop more than what the tract is going to force you to have. 20 traverse points on the North, 20 traverse points along the South and one on each of the East and West lines is bad enough.
Kris
Kris,
A traverse is a series of turned angles and measured distances. If you agree that, all other things being equal, error ellipse propagated for a 15 degree angle is the same as for a 90 degree angle, then by logical extension it doesn't matter if the traverse is composed of a series of 15 degree angles or 90 degree angles. The orientation of the error ellipses will be different but the size will be the same.
In a traverse, the magnitude of the angles does not matter but rather the accuracy of the angles.
Peter Lazio
Kris
Kris,
I'm trying to get an idea of what your objection is to the traverse you described.
If you had to survey that 300' x 4000' rectangular tract, and were unlimited by time constraints, and had permission to extend your traverse on the adjoiners as far as you wanted, what shape traverse would you choose?
- Doug
Jeff,
You're not missing anything. I'm surprised at how much misinformation has been presented here.
- Doug
> This topic deserves a more detailed discussion, because the myth is so prevalent. I don't have enough time this week, though.
>
> Maybe this weekend we could post the coordinates of a 6-corner tract, and ask posters to suggest "good" traverses as well as ones with "weak angles." Then we can analyze the survey designs with a preanalysis program like Star*Net and separate the myth from the truth.
That would really drain the swamp of ill-informed ideas about traverse geometry that have been posted here. A numerical example is clearly needed.
Kent
I agree!
Didn't you post something along those lines a few year back?
Loyal