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Open Traverse closing method

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amksyr
(@amksyr)
FNG Member

Dear Senior Surveyors

I want to ask about open Traverse that what method should I adopt for closing open Traverse 

1) Bowditch (compass) rule or

2) Angular method

My confusion is when I adopt Bowditch rule traverse close on last point and I get exactly same coordinatea of last point

But if when I adopt angular method I got different coordinates of last points 

When to use Bowditch rule and when to use Angular method.

Please guide me if you understand my question or if you need any clarification let me know thanks.

My Introduction

my name is Muhammad Aamir I am from Pakistan my Native language is Urdu So if you found grammar mistake please forgive me thanks.

This topic was modified 2 years ago by amksyr
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Topic starter Posted : January 7, 2020 3:23 am
Charles L. Dowdell
(@charles-l-dowdell)
500+ posts Member

Here is an excerpt from one of my surveying books I have in my library and the formula for the calculations of the Convergency of Meridians from an old K&E Ephemeris. The only check on an open traverse is angular, essentually by taking astronomic observations at each end and checking the angular error and comparing to the calculated convergence bearing/azimuth at the end.

 

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Posted : January 7, 2020 11:37 am
Jon Payne
(@jon-payne)
500+ posts Member

Assuming it is an open traverse (as opposed to a linked traverse), you are missing 'knowns' at the end of the traverse with which to close anything.  Therefore you would not be able to adjust the angles because you would not have a known azimuth your should be matching at the end.

The method you need to adopt would be to either establish known and related  beginning and end points making the open traverse a linked traverse or make additional measurements to wrap the traverse around and make it a closed figure.

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Posted : January 7, 2020 11:39 am
amksyr liked

JerryS
(@jerrys)
500+ posts Member

At the risk of exposing my own ignorance, the "angular method" adjustments I am familiar with only were designed to distribute the gross angular misclosure among the traverse stations, the assumption being that the angular misclosure was the result of systematic error in the equipment that could not be eliminated other than by adjustment once the gross angular misclosure is quantified.  This error can be minimized by taken multiple reading in both face 1 and face 2 orientations of the total station.

The Bowditch or Compass Rule adjustment divides the linear misclosure proportionally among all the traverse stations, so that each leg of the traverse gets the proportional amount of its length as a percentage of the overall traverse length.

Either adjustment method presumes that there are no blunders, and that you are distributing the misclosure through the traverse.  Some would first do an angular adjustment to balance the angular misclosure though all the traverse stations, as quantified by a reoccupation of the initial survey station, with a backsight taken on the last station and the angle turned to the second traverse station.  If the raw error of closure before any adjustment is small, my experience is that an angular adjustment before doing the Compass Rule adjustment will result in a slightly poorer linear misclosure than prior to adjustment.

The experts on this site would encourage you to take multiple measurements to each forward station and to use least squares to do your traverse analysis and adjustment.

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Posted : January 7, 2020 11:49 am
Dave Karoly
(@dave-karoly)
10,000+ posts Member

I'm not sure if the traverse runs from one pair of known control points through several new traverse points to another pair of known control points.

-OR-

If it is a closed loop starting on a pair of traverse points and ending on the same pair and the term 'open' is being used to mean 'unadjusted.'

At any rate, balancing the angles then recalculating the traverse will not result in a closed, adjusted set of coordinates.

You can do a Bowditch Adjustment with the angles unbalanced or balance the angles then do a Bowditch Adjustment (common procedure back in the old days).

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Posted : January 7, 2020 11:53 am
amksyr
(@amksyr)
FNG Member

@dave-karoly

Sir it's a open Traverse which starts on the known point and end on unknown point after 4 kilometer in length from starting known point. It's parallel to the road.

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Topic starter Posted : January 7, 2020 12:00 pm

Bill93
(@bill93)
5,000+ posts Member

If there is no check measurements or redundancy, there is nothing to adjust.  A sketch or list showing which angles and distances were measured and what was taken as given (such as starting coordinates) is needed for us to see your situation and determine if an adjustment can be done.

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Posted : January 7, 2020 12:28 pm
Andy J, JPH, NorthernSurveyor and 1 people liked
Dave Lindell
(@dave-lindell)
1,000+ posts Supporter

There is no adjustment possible.  You have nothing to adjust to.  Your measured values to the final point of unknown anything now make it known by your measurements.

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Posted : January 7, 2020 12:33 pm
amksyr
(@amksyr)
FNG Member

Ok Sir currently I am login on mobile I will attach sketch and data tomorrow thanks 

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Topic starter Posted : January 7, 2020 12:34 pm

Geomatician
(@geomatician)
FNG Member

@charles-l-dowdell

Author Barry F Kavanagh? I got the 6th edition (2003) 😉  

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Posted : January 7, 2020 2:49 pm
amksyr liked
Charles L. Dowdell
(@charles-l-dowdell)
500+ posts Member

@geomatician

Barry F. Kavanagh & S.J. Glenn Bird, 1984. Probably First Edition, as it doesn't say.

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Posted : January 7, 2020 3:40 pm
amksyr liked
spledeus
(@spledeus)
1,000+ posts Member

So you have a point and a point and you traversed between?  Think it through for a moment.  If you had a bearing and a bearing, you could adjust the angles then apply the bowditch.  The best you can do is essentially scale from point to point.  What is the misclosure?  Where did you get your points from?  What is your altitude and do you have to worry about scale factor?  The flat angles along a road add another concern due to lack of strength of geometry.

 

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Posted : January 7, 2020 5:45 pm
amksyr liked

Bill93
(@bill93)
5,000+ posts Member
Posted by: @spledeus

The flat angles along a road add another concern due to lack of strength of geometry.

While there are certainly concerns here about the lack of checking, strength of geometric figure is not among them here. 

When you are measuring angle and distance with comparable accuracy there is no such thing as a poor angle.  Poor angles are those used without distances to form an intersection of lines that are too close to parallel, what I call the scissors effect.

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Posted : January 7, 2020 7:30 pm
amksyr liked
amksyr
(@amksyr)
FNG Member

Thank you very much all the senior members thanks for helping me I got lot of information from your replies and what I figure out is that

I cannot close this traverse because the end point is unknown the only way to check the error is if I have a known point at the end. 

in my Traverse i didnot have any refference to close it or Re check it.

Also i  get information from this survey computations - UNSW Engineering PDF file from the internet which is explaning about the open traverse I have study this book and now I have two questions in my mind that

case 1)

if I have two known points at the beginning of open Traverse and two known points at the end of open traverse then how I close the traverse or which method should I use.

  Page 119 ~ Page 127 
case 2)

if I have two known points at the beginning of the open traverse and one known point at end of the open traverse.

note : I am asking this for learning purpose I didn’t have any known point at my project except at beginning I am using Leica Ts 12 Total Station.

thanks again for taking time to answer my problem from your precious Time.

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Topic starter Posted : January 8, 2020 3:23 am
amksyr
(@amksyr)
FNG Member

@spledeus

Dear Sir incase if i have Bearing (Azimuth ) of Start Known points and Bearing of Last Known Points then first i have to go for angle adjustment and then i apply the bowditch rule ? 

 or i can directly go for bowditch rule without adjusting the angle ?

ReplyQuote
Topic starter Posted : January 8, 2020 3:30 am

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