INTRODUCTION TO TRAVERSE SURVEYING
- Traversing is a method of control survey to establish control points. A traverse must start with control station which is known station (known coordinate). It is a method of transferring coordinates.
- Definition Traverse – a series of points (stations), each one intervisible with its adjacent points. The lines joining these stations are the traverse lines, consists of the measurement of angles (bearing) and length (distance) of each line.
Types of traverse:
- Open traverse
- Begin with known point and end with unknown point
- Cannot checked and adjusted
- Useful when the survey is a long narrow strip
- Close traverse
- Begins and ends on the same point or begin with known point and ending to another known point.
- Can checked and adjusted
- Traverse which complete cycle is made.
Purpose of traverse
- Surveying details
- A traverse network of survey line and ground marks provides control points which can be accurately plotted in a map or plan
- Setting out
- To position of road, building or other new construction.
- Pegs can then be set out on the ground from the traverse to define the position of design points (road, building, etc.)
- Property survey to establish boundaries.
- Ground control surveys for mapping purposes.
Measurement in traverse:
- Angle measurement (bearing)
- Linear measurement (distance)
Instrument used for traverse:
- Total station
- Prism (reflector)
- Prism pole
- Reconnaissance Survey
- Station Marking
- Observation, Measurement & Booking
- Data Processing & Observation Checking
1) Reconnaissance Survey
Is a process to get general view (picture) of the site. Carried out to determine and selection of suitable station points. The criteria for selection of station points:-
- Use “whole to part “ principle.
- Aiming for good visibility between stations and bearing in mind any subsequent setting out. The station must be available to observe all the detail surrounding.
- The number of station must be minimize but cover all the survey site.
- The distance between station must be far (more than 30 m) and same as other traverse line.
- Avoid the sight line to close with earth surface.
- Station must be at the stable surface.
- Try to avoid any disturbance such as tree, building etc.
“Whole to part” Principle
- According to this principle, it is always desirable to carryout survey work from whole to part. This means, when an area is to be surveyed, first a system of control points is to be established covering the whole area with very high precision. Then minor details are located by less precise methods.
- The idea of working this way is to prevent the accumulation of errors and to control and localize minor errors which, otherwise, would expand to greater magnitudes if the reverse process is followed, thus making the work uncontrolled at the end.
2) Station Marking
The station can be mark when the station criteria had been full fill. The common station marking are wood peg and nails. The selection of the station marking depend on the site condition.
- If the survey works on the road, the suitable marking is nails.
- If the survey works in the forest or construction site, the wood peg is the best used as station marking.
- For permanent marking, the station can be in concrete.
3) Observation, Measurement & Booking
There are two types of observation & measurement in traverse:-
- Bearing – measure angle from the north in clockwise direction
- Distance – measure distance of the traverse
The observation begin with back station to front station.
The observation must be done in face left and right.
The suitable observing sequence being:
- Set bearing back station, face left.
- Observe fore station, face left.
- Set bearing back station, face right.
- Observe fore station, face right.
4) Data Processing
- Site calculation
- Mean bearing
- Correction using bearing comparison method
- Final bearing & final distance
- Office calculation
- Latitude & departure
- Linear misclosure
- Adjusted latitude & adjusted departure
- Final coordinates.
There are three types of checking bearing and angle:-
A) Total internal and external angle
Σ (Internal Angle) = [2n-4] 90º
Σ (external Angle) = [2n+4] 90º n = total number of stations.
B) Bearing comparison
The last bearing is compare with the establish or known bearing value.
Line AB read as 29º 29’ 21”
Suppose read as 29º 29’ 29” Angle misclosure – 8” in 4 station a, b, c and d. Adjustment +2” per station.
The checking was done by observation to the other reference station and compare the difference
SPECIFICATION AND ACCURACY
Linear Misclosure that recommended by Department Survey and Mapping
|TYPE||ACCURACY||PURPOSE||ANGLE MEASUREMENT||DISTANCE MEASUREMENT|
|Geodetic||1 : 50000
||Theodolite 0.1”||1. EDM|
|General||1 : 5000
1 : 5000
- Plotting is a process to produce output product of traversing; map or plan.
- By using final coordinates data or final bearing and final distance.
- plans are drawn or printed on paper, but they can take the form of a digital file.
Criteria and element of traverse plan
- Elements of a detail Plan
- Title Block
- Location Plan
- Control Grid
- North Arrow
- Key (legend)
ERRORS IN TRAVERSE SURVEYING
- Instrumental error
- Personal error
- Natural error
- No Permanent Adjustment
- Do Permanent Adjustment
- Multiple observations ( Face left /face right)
- Error of Manipulation
- Inaccurate centering
- Inaccurate levelling
- Non – elimination of parallax
- Error of Observation
- Inaccurate bisecting signal
- Non vertical signal
- Displacement of pegs / signal
- Wrong Reading & Booking
- High temperature
The source of errors during observation are:
- Total station is not perpendicular to the station
- Total station is not level during observation
- Wrong handling theodolite and tripod
- Effect from curvature and refraction
- Error in reading or booking