TRAVERSE GEOM2015

8/14/2019 TRAVERSE GEOM2015

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INTRODUCTION

In this assignment students were assessed based on their knowledge and skill in establishing both

horizontal and vertical control for the area around the University of the West Indies, St.

Augustine Campus, StudentsAdministration Building. Students were expected to traverse and

to undertake a leveling loop and appropriately reduce all data to establish a vertical datum. Thefollowing defines a methodology which can be applied for any area needed to undertake leveling

loops as well as traverse circuits, as well as any corrections, reductions needed, checks to ensure

accuracy and verify said methodology, lastly presents results, sample calculations, assumptions

and scopes for improvement.

AIM

In this assessment, it was required to undertake a traverse to establish XY coordinates for the

Students Administration Building and to also undertake a leveling loop and thus appropriately

reduce all data to the established datum.

LITERATURE REVIEW

The Group is given a range of 4-5 points to undertake traverse circuit, 4 points were chosen since

the area was considered reasonably small and visibility towards each corner was very high. A

primary bearing was assumed to be 000. The solution to this problem is as thus; An initial

sketch on site was performed of the area, labeling each of the four corners A, B, C, or D

respectfully. The total station is then set up at point A and focused to Point B, readings of angle

and distance were taken for both face and face left, three times each, the same was repeated for

all corners, each time sighting the two visible points. Data was then organized, tabulated on site,

next angle of misclosure was determined, bearing in mind:

Sum of deflection angles = 360 Sum of internal angles = (2n-4) x 90 Sum of external angles = (2n+4) x 90.

Since there were four stations set ups the sum of internal angles were to add up to 360 and

external angles 720. The distributed angular error was taken into account this is taken as 15cumulative and therefore after each angle, the adjusted angle is given as: Angle-4. In the

Computation of bearings, after finding the first bearing (in this case it was assumed to be

000, the next bearing is determined by the back-bearing (previous bearing 180) + angle (if>360 subtract 360). The Polar coordinates must now become rectangular coordinates; these arethe Eastings and Northings. The primary easting for a localized site is set to 3000 and primary

northing set to 4000. Therefore the E & N can be computed from the following;

E= L sin

N = L cos

N

L

A

B


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The changes in Eastings and Northings can now be computed and added to the original 3000 and

4000 readings assumed primarily or from whichever point L is taken from; these new values are

the coordinates of the points plotted before, in space. Tabulating all values of E & N some

will be negative, some positive, their sum should add up to 0, if not for this error, the

linear misclosure must be determined, here e=

))

. Now the Proportional Misclosureneeds to be computed; this is the ratio of 1:

. If the linear misclosure is

within the proportional misclosure, the error can be fixed by use of the Bowdich Method, if not,

transverse must be retaken. The Bowdich method of Correction, firstly dividing distance L by the

perimeter then multiplying it by the error to obtain N or to obtain E. The differencebetween both E&E and N&N, added to the coordinates reason out errors and produce

accurate readings.

Leveling loops are achieved when the surveyor starts and ends on the same position, on viewing

from the levels telescope; the lowest staff reading is the vertical height. This is firstly taken as a

backsight, from a benchmark of known height (can either be a Temporary Bench Mark, TBM or

Permanent Bench Mark), succeeding this all points where there seems to be a change in slope is

observed these are taken as foresight. If there comes a point where the staff can no longer be

seen from the Level then a change point is needed, the level is set up at a new location where the

staff can once again be read also once again a backsight from a known benchmark (usually last

point measured from level) is needed to start.

Booking Data, using the method known as Rise and Fall method, this is achieved by starting off

with the primary backsight reading, using the following foresight simply subtract the latter from

the former, if it is positive it is recorded as a rise by the amount of the difference, if negative it is

recorded as a fall by the amount of the difference and the minus sign disappears. This comes in

handy when dealing with the reduced level; as the leveling loop started off at a known bench

mark height whenever there is a fall the height drops by the amount of the fall, whenever there is

a rise it increases by the amount of the rise. To ensure proper readings were taken sum of

BS&FS readings should be equal to the sum of rise & falls. On average, the acceptable

misclosure allowed in construction applications is 12mm, if the achieved misclosure goes over,

re-observations are needed, if not, then the error must be dived by the number of setups and

added to the final level reading. Levels are considered accumulative and therefore the error is as

well, therefore the ratio of

)must be implemented wherex represents the setup currently

being calculated, e represents the error and n the number of setups. This ratio is added to each

reading corresponding tox and adjustment is recorded.


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METHODOLOGY

This methodology is broken up into two parts:

Traverse

Leveling loop

Four control points, labelled A, B, C and D were stationed along the building at strategic points

so as to ensure visibility when acquiring readings from the total station. This was done by

positioning range poles at each control point and checking visibility from each point. The control

network set up can be seen in the witness diagram. The assignment itself took two days to

complete therefore the witness diagram was necessary so as to provide easy access to the points.

All measurements made on the witness diagram was done via the measuring tape. The traverse

and leveling loop were carried out separately but it should be noted the same control points were

used. It also should be noted that for the site diagram drawn up for the level that the level was

located approximately midway between each point for which backsight and foresight readingswere to be obtained. Below is a list of equipment used in this assignment:

Prism Pole Prism Total Station 4 pegs 3 chaining pins (pairs) Measuring tape Hammer

Level (automatic) Staff

Traverse

1) The total station was set up and properly leveled at point A.2) A prism pole along with its prism was located at point B then D and sighted respectively

through the total station so as to obtain to corresponding distances for those points

3) Next chaining pins were placed at control points B and D.4) The total station was then sighted at the base of the chaining pin situated at point B. This

reading was then recorded and placed in the data sheet.

5) The total station was after targeted at the base of the chaining pin situated at point D. Thisreading was then recorded and placed in the data sheet.

6) Steps 3-4 were repeated to obtain multiple readings of different zeroes on the total stationto ensure consistency of the horizontal angles which were all reduced in the field notes

before proceeding to another point.

7) Steps 1-5 were repeat at points B through D ensuring that all data was reduced andconsistent or acceptable before proceeding to a next control point.


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Leveling loop

1) A two-peg test was firstly done to ensure that the instrument was fully functioningbefore proceeding with assignment.2) A site map was drawn up of the area locating points on the diagram where turning points(black markers) were to be located and thus the position where the level was to be set up

(blue markers). (see site map for more clarity)

3) The level instrument was set up at station A.4) A staff was then placed at the benchmark (stp5) so as to obtain a backsight reading of the

point by sighting the staff through the level.

5) Next point P, with a staff placed at its location, was sighted through the level so as toobtain a foresight reading for that point.

6) Both foresight and backsight readings were then placed in the booking sheet given.7) Steps 2-5 were repeated for points B-Fon the site diagram being where the level was

set up each time so as to obtain backsight and foresight readings for points A-D.

8) Step 6 was repeated in an anti-clockwise direction i.e. from F-B thus obtainedbacksight and foresight readings for turning points D-A respectively. This was done as a

filed check to ensure that all points are on par with each other.

9) Finally to complete the loop, the level was set up at position A so as to sight thebenchmark and obtain final foresight and backsight readings.


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FIELD DATA AND DIAGRAMS

Traverse

Horizontal Angles Mean

FL and FR

Reduced to RO Distance

(m)TargetStation Face Left Face Right " " " "

A-B 195 29 50 15 30 7 195 29 59 0 0 0 56.333

A-D 287 0 59 107 1 35 287 1 17 91 31 18 43.194

B-C 291 19 20 111 19 56 291 19 38 0 0 0 47.872

B-A 9 7 33 189 7 18 9 7 30 282 12 8 56.338

B-C 230 0 3 50 0 35 230 0 19 0 0 0 47.872

B-A 307 47 58 127 48 28 307 48 13 282 12 6 56.338

B-C 170 0 0 350 0 31 170 0 16 0 0 0 47.872

B-A 247 47 54 67 48 13 247 48 4 282 12 12 56.338

C-D 290 0 0 109 58 35 289 59 18 0 0 0 47.534

C-B 27 48 40 207 46 27 27 47 34 262 11 44 47.878

D-A 290 0 0 109 59 18 289 59 39 0 0 0 43.198

D-C 22 47 35 202 47 49 22 47 42 267 11 57 47.538

D-A 230 0 0 50 0 20 230 0 10 0 0 0 43.198

D-C 322 48 45 142 48 58 322 48 52 267 11 18 47.538

D-A 170 0 0 350 0 4 170 0 2 0 0 0 43.198

D-C 262 49 0 82 49 3 262 49 2 267 11 0 47.538

N

B C

A

D

ADMIN


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Leveling loop

FROM B.S I.S F.S Height of

Collimation

Distance Reduced

Level

Remarks and

Diagram

STP5 1.324 15.050 13.726 B.M STP5 to P

A 1.832 0.568 15.912 14.08 P-AB 1.778 0.970 16.720 14.942 A-B

C 1.611 1.233 17.098 15.487 B-C

D 1.204 1.499 16.803 15.599 C-D

E 1.343 1.648 16.498 15.155 D-AF 1.488 1.555 16.431 14.943 A-DG 1.725 1.277 16.879 15.154 D-C

H 1.559 1.282 17.156 15.597 C-BI 1.225 1.669 16.712 15.487 B-A

J 1.025 1.769 15.968 14.943 A-PK 0.613 1.886 14.695 14.082 P to B.M STP5

L 1.367 13.328 11.961

N

B D' C

C'

E'

A F'

P

A'STP 5

B'

D

LRC CAR PARK

CARPARK

ADMIN

Green Anti-Clockwise

Pur le Clockwise

SITE MAP


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Error in leveling loop = Total BacksightTotal Foresight = 0.004m

Allowable error = 5*(where n=number of turning points)

= 5*= 0.012m

RESULTS

Traverse

From To Observations Bearing Corrected

bearing

Distance DN DE Northing Easting

N

B C

A

D

ADMIN


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Leveling loop

FROM B.S I.S F.S Height of

Collimation

Distance Reduced

Level

Remarks and

Diagram

STP5 1.324 15.050 13.726 B.M STP5 to P

A 1.832 0.568 15.912 14.08 P-AB 1.778 0.970 16.720 14.942 A-B

C 1.611 1.233 17.098 15.487 B-C

D 1.204 1.499 16.803 15.599 C-D

E 1.343 1.648 16.498 15.155 D-AF 1.488 1.555 16.431 14.943 A-DG 1.725 1.277 16.879 15.154 D-C

H 1.559 1.282 17.156 15.597 C-BI 1.225 1.669 16.712 15.487 B-A

J 1.025 1.769 15.968 14.943 A-PK 0.613 1.886 14.695 14.082 P to B.M STP5

L 1.367 13.328 11.961


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DISCUSSION OF MEASUREMENTS AND FINDINGS

Whilst conducting the Transverse loop many assumptions were made firstly we assumed our

primary bearing, from a known point to be 000, following we assumed the primary XY

coordinates to be 3000, 4000. Angles are always made to never be 90 each either had to be

between 0 and 90 or between 90 and 180, witness points were placed as permanent structuresso checks can easily be made, reading were taken three good rounds each for both face right and

face left angles were reduced by subtracting 180from the face right and comparing to face left,

this also provided a check. Distances were measured both with total station and measuring tape

for accuracy. Whilst conducting the leveling circuit readings; firstly, the two peg test was

conducted to calculate the error within the instrument, this error was later reduced from readings

accumulatively (in ratios). Readings were ensured to be less than 50 meters for the sake of

readability of the staff, the settlements were always taken into account for placement of staff

(always on concrete, never on grass), placement of tripod (no flowing soils). All checks were

conducted on sight meaning the sum of BS&FS= sum of rise & falls. Small errors occurred

throughout the both procedures meaning both the prism for the traverse and the staff for the

leveling were not always held upright, there maybe was leveling bubble errors in any of the

pieces of equipment. But mostly the greatest errors occurred due to the curvature and refractions

of the land as well as the inclement weather, which always caused the stopping of the operation

for the sake of the protection of equipment.

Validations

In terms of a validation method, in addition, two measurements for distance between two points

were acquired and assessed between each other. The compared distance values were shown to be

similar with a difference of 4mm, 5mm and 6mm. In addition, three sets of angles were taken,both a Face Left and a Face Right. The zeroes which was different for each angle were taken at

60 degrees angle intervals each until the third zero. The difference was taken between the first

and second angle reading, and the third and fourth angle reading. The differences were compared

with the intervals of the zero and was shown to be comparable with a difference of 11919, 3,

11917, 9,1 10,10,31,8.Also another way the readings were validated was that of the

anti-clockwise method used in the leveling loop where the difference in height between the first

clockwise loop would be equal to the difference in height in the anticlockwise loop seeing

that the level is being done of the same building based on the same control points. Distances

were also measured using the measuring tape along with the total station by means of a way to

ensure that the readings obtained from the total station was accurate. Finally for the leveling loop

it was validated by means of the loop method itself seeing that it started and ended at the

benchmark meaning the heights at both points could be validated.


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LIMITATIONS

Traverse

1) The locking mechanism on the total station was not functioning properly meaning shiftscould have taken place during readings and measurements.2) Visibility was obstructed at certain times since the building under survey was surroundedby car parks on the east and south side of the building.

3) The building was located in an area where heavy student traffic took place also aPasserby knocked down one of the chaining pins situated at a control point thus affecting

the readings.

4) Rain was a pressing factor seeing as the instruments could not be exposed to water,therefore in some cases readings were taken hurriedly introducing some form of error in

readings.

Leveling loop

Limitations with respect to the leveling loop was almost negligible seeing as the error with the

loop (4mm) falls far below the allowable limit (12mm) therefore it can be assume that there is no

real error with this procedure. The only limitation that may seem important to mention is the

holding of the leveling staff which is prone to human error as the individual may sway it at

random intervals thus affecting the readings.

SCOPE FOR IMPROVEMENT

Traverse

1) Acquire a fully functioning device i.e. with proper locking mechanisms.2) Further reduce results before proceeding.3) Firmly plant chaining pins in the ground so as to avoid passers by causing an

interference.

4) Account for an influx of cars at certain times because of surrounding parking lots.Leveling loop

As mentioned in the limitations section, there is no real error in the procedure but there is always

a place for improvement. With respect to the improvement itself, the only area of improvement

can be in the holding of the leveling staff and with the setting up of the instrument seeing as theerror in the device was gotten rid of at the start using the two-peg test.


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CONCLUSION

The traverse was undertaken and hence XY coordinates were established along with a leveling

loop of said building. All data was reduced to UWI control network and can be seen in the tables

of results.

TRAVERSE GEOM2015

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