SITE OF SURVEY

The Levelling survey was carried out from Afe Babalola to

The Faculty of Arts of The University of Lagos (Akoka),
Lagos. The faculty is adjoins Faculty of Law and Faculty of
Business Administration. One of the major monuments along
the site of the survey is the UNILAG Senate Building.
OVERVIEW OF THE PRACTICAL
For the purpose of simplicity, the whole project can be
summarized under the following basic operations, following
the sequence presented:
1)Reconnaissance
2)Collection and Test of instrument
3)Data acquisition
4)Data processing
5)Data presentation

RECCONNAISSANCE

In surveying, reconnaissance is very important because it

covers all aspects of the project before the actual site work.
It also gives details on what is to be done and prevents poor
production. Reconnaissance was done before the practical
was carried out on the site. It was divided into two aspects,
which were:
 Field reconnaissance
 Office reconnaissance
FIELD RECCONNAISSANCE
Field reconnaissance involved, going to the proposed site to
inspect it’s environ and to check how conducive the site was.
At the site, the boundary points/ nail points were picked and
marked out after considering a number of factors given
below:
 Intervisibilty of points or stations
 Distance between stations
 Possibility of setting up on that station
 Proximity to the road
 Ease of distance measurement without vehicle
interference
A rough sketch of the site (Recce Diagram) was drawn on
the field to serve as guide during the practical. During the
reconnaissance, a set of controls discovered close to the site
and noted, to serve as the reference station for the survey
job. The controls discovered were; GME 05 and GME 06.
OFFICE RECCONNAISSANCE
Next was Office Reconnaissance. This involved planning on
the data acquired on the field and strategizing on how best
the practical could be performed. The instruments used
were collected from theUniversity of Lagos, Surveying and
Geo-informatics storeroom. The coordinates of the controls
located were collected from the Surveying and Geo-
informatics departmental office. The coordinates of the
controls collected were

CONTROL NORTHIN EASTING(m HEIGHT(m

G (m) ) )
GME 04 720567.44 543880.665 8.165
(Afe 4
Babalola)
GME 05 720627.62 544028.845 7.965
(Faculty of 2
Arts)
GME 06 720553.12 544116.346 6.902
(Faculty of 2
Engineering
)
LEVELING
DEFINITIONS OF LEVELLING

Leveling is the process of finding the height of a new point or

points by comparison with that of an existing point which
has been selected as a datum or whose height is already
known with respect to some other datum.

Leveling is the most widely used method for obtaining the

elevations of ground points relative to a reference datum
and is usually carried out as a separate procedure from that
used for fixing planimetric position.
Leveling involves the measurement of vertical distance
relative to a horizontal line of sight. Hence it requires a
graduated staff for the vertical measurements and an
instrument that will provide a horizontal Line of sight.

LEVELLING TERMS

REFERENCE DATUM
A datum is any reference surface to which the elevations of
points are referred. This is the surface that is arbitrarily
assigned an elevation of zero the most commonly used
datum is that of mean sea level (MSL).
REDUCED LEVEL (RL)
The RL of a point is its height above or below a reference
datum

BENCHMARK (BM)
A benchmark is best described as a permanent, solid point of
known or assumed elevation above or below a reference
datum. Common examples are metal disks set in concrete.
Types include:
 Cut bench marks
 Flush brackets
 Bolt bench marks
 Fundamental bench marks (FBM)

FOCUSSING
It means to set the eyepiece and the object glass at proper
distance apart for the clear vision of the object sighted. The
focus of the objective and that of the eye-piece must coincide
with the cross-hair of the diaphragm, as the diaphragm is
placed at the common focus. This can be done by first
focussing the ye piece and then the object-glass

HEIGHT OF INSTRUMENT
It is the elevation or reduced level of the line of collimation
when the instrument is correctly levelled.
FORESIGHT
It is a staff reading taken on a point whose reduced level is to
be determined. It is the last staff reading taken before the
shifting of the level.
BACKSIGHT
It is a staff reading taken on a point of known reduced level
as on a bench mark or a change point. It is the first staff
reading taken after the level is set up and levelled.
INTERMEDIATE SIGHT
It is any reading other than foresight and back sight taken on
a point of unknown R.L from the same set up of the level. All
reading taken between the back sight and foresight reading
are called intermediate sight reading.
MEAN SEA LEVEL
It is the average height of the sea’s surface for all stages of
the tide over a 19 year period. It is the imaginary level from
which heights and depths are calculated, taken at a mean
distance between high and low water.

CHANGE POINT
Change point is a station where backsight and foresight is
taken
LEVEL LINE / SURFACE
A level surface is a curved surface that at every point is
perpendicular to the direction gravity as indicated by a
plumb line. A level surface is usually spheroidal in shape. A
body of still water is the closest example of a level surface. It
is also known as a reference datum since points using this
datum have heights relative to this surface.
A level line is a line in a level surface which at all points is
normal to the direction of the force of gravity as defined by a
freely suspended plumb-bob.

HORIZONTAL LINE
A horizontal line or surface is one that is normal to the
direction of the force of gravity or the local vertical line at a
particular point.

VERTICAL LINE
A vertical line that follows the direction of gravity as
indicated by a plumb line.

EQUIPMENTS
 STAFF/ LEVEL RODS
 THE DIGITAL LEVELLING STAFF
 LEVEL
The level is one of the most versatile instruments used by
field engineers.A level is an instrument that comprises a
telescope (to create a line of sight and enable reading to be
taken on the staff), and a system to orient the line of sight in
a horizontal plane.
Types of Level are listed below:

 TILTING LEVEL
 AUTOMATIC LEVEL
 DUMPY LEVEL
 DIGITAL LEVEL

THEORY

TECHNIQUE
The level is an optical instrument that provides a height
reference. This reference is a horizontal plane through the
axis of the telescope, known as the "Height of Collimation".

Once the height of collimation (or instrument height) has

been measured, the height of other stations can be found by
measuring from this plane with a staff.
The height of collimation is found by taking a back sight to a
staff placed on a bench mark. The staff reading is added to
the bench mark value to obtain the height of collimation.

Once the height of collimation has been found, ground height

at any spot below this plane can be found by observing the
staff and subtracting the staff reading from the height of
collimation.
PRINCIPLE OF LEVELING
All level instruments are designed around the same
fundamental relationships and lines. The principal
relationships among these lines are described as follows:
 The axis of the level bubble (or compensator) should
be perpendicular to the vertical axis.
 The line of sight should be parallel to the axis of the
level bubble.

The instrument was set up and correctly leveled in order to

make the line of sight through the telescope horizontal.
Vertical measurements from this plane, using a graduated
leveling staff, we enabled the relative elevations of ground
points to be ascertained. Consider Figure A with the
instrument set up approximately midway between ground
points A and B. If the reduced level (RL) of point A is known
and equal to 100.000 m above OD (AOD), then the reading of
3.000 m on a vertically held staff at A gives the reduced level
of the horizontal line of sight as 103.000 m AOD. This sight
onto A is termed a back sight (BS) and the reduced level of
the line of sight is called the height of the plane of
collimation (HPC). Thus:

RL.A + BS = HPC

The reading of 1.000 m onto the staff at B is called a

foresight (FS) and shows the ground point B to be1.000 m
below HPC; therefore it’s RL = (103.000 − 1.000) = 102.000
m AOD. An alternative approach is to subtract the FS from
the BS. If the result is positive then the difference is a rise
from A to B, and if negative a fall,
i.e. (3.000 − 1.000) = +2.000 m rise from A to B;
Therefore, RLB = 100.000 + 2.000 = 102.000m AODB. This
then is the basic concept of leveling which is further
developed.
METHODOLOGY
STEPS IN TAKING READINGS
1. Set up the instrument on a firm, secured tripod base.
2. Centralize the circular bubble using the foot screws or
ball and socket arrangement.
3. Eliminate parallax.
4. Centre the vertical cross-hair on the leveling staff and
clamp the telescope. Use the horizontal slow motion
5. Screw if necessary to ensure exact alignment.
6. Focus onto the staff.
7. Carefully center the tubular bubble using the tilting
screw.
8. With the staff in the field of view, note the staff reading
and record it.
Operations (4) to (7) must be repeated for each new staff
reading.

METHODS OF BOOKING
STATION BACK FORE RISE FAL REDUCED DISTANCE HEIGHT OF REMARKS
SIGHT SIGHT L LEVEL INSTRUMENT
GME05 NL1
NL1 NL2
NL2 GME06

RISE-AND-FALL

HEIGHT OF COLLIMATION

COMPARISON OF METHODS
The rise-and-fall method of booking is recommended as it
affords a complete arithmetical check on all the
observations. Although the HPC method appears superior
where there are a lot of intermediate sights, it must be
remembered that there is no simple straightforward check
on their reduction.
The HPC method is useful when setting out levels on site. For
instance, assume that a construction level, for setting
formwork, of 20 m AOD is required. A BS to an adjacent TBM
results in an HPC of 20.834 m; a staff reading of 0.834 would
then fix the bottom of the staff at the required level.

BOOKING
 Successive rows of entries on the form refer to successive
staff stations; the foresight from I1 and the back-sight from
I2 (both to staff position B, in Figure B) are therefore booked
on the same line. At each instrument station, the height of
the line of collimation is obtained from the back-sight, and
then the reduced level of the next foresight is calculated by
subtracting the relevant staff reading. The booker, who may
well also be the observer, books each reading in the field
book as it is taken, using a pencil or ball-point pen. Fill in a
name for each staff station; the entries in the distance
columns need only be approximate and can be judged by
pacing. Do not erase; make corrections by drawing a single
line through the incorrect figures, leaving them legible and
writing the correct figures above them. A fair copy can be
made later on another page if necessary, but take care to
avoid copying errors, and do not destroy the original papers.
Sign and date the work. Immediately after booking a reading,
verify it by again looking through the instrument; beware of
gross errors of a meter or a tenth of a meter. Then look at the
bubble again to verify that the instrument is level.

NATURAL ERRORS
INSTRUMENTAL ERRORS
  Line of sight

 Parallax error

 Rod not of correct length

 Tripod legs loose

PERSONAL/OBSERVATIONAL ERRORS

SYSTEMATIC ERRORS

CLOSURE TOLERANCES

It is important to realize that the amount of misclosure in

leveling can only be assessed by:

 Connecting the leveling back to the BM from which it

started, or
 Connecting into another BM of known and proved
value.

When the misclosure is assessed, one must then decide if it

is acceptable or not.
In many cases the engineer may make the decision based on
his/her knowledge of the project and the tolerances
required.
Alternatively the permissible criteria may be based on the
distance leveled or the number of set-ups involved. A
common criterion used to assess the misclosure (E) is:
E = m(K)1/2

ERROR DISTRIBUTION

The misclosure cannot be ignored and the error must be

distributed among the points concerned. In the case of a
leveling circuit, a simple method of distribution is to allocate
the error in proportion to the distance leveled. For instance,
consider a leveling circuit in FIGURE D below, commencing
from a BM at A, to establish other BMs at B, C,D and E for
which the heights have been computed without taking the
misclosure into account.

On completing the circuit the observed value for the BM at A

is 20.018 m compared, with its known and hence starting
value of 20.000 m, so the misclosure is 0.018 m. The distance
leveled is 5.7 km. considering the purpose of the work, the
terrain and observational conditions; it is decided to adopt a
value for m of 12 mm. Hence the acceptable misclosure is
12(5.7)12 = 29 mm, so the leveling is acceptable.

ARITHMETICAL CHECK:
The difference between the sum of back sights and the sum
of fore sights is equal to the difference between the sum of
the rise and fall and was equal to the difference of first and
last R.L. The R.L. of A was known, the R.L. of B was calculated
by the following relation: R.L of B = ΣR.L. of A + ΣB.S. -
ΣF.S.The R.L. There was no intermediate if there was any
points may this be found by the following relation: R.L. of a
point = R.L of B.M + B.S. - I.S The difference of level between
A and B was equal to the algebraic sum of these differences
or equals the difference between the sum of back sights and
the sum of the foresights (ΣB.S - ΣF.S.). If the difference was
to be positive, it would have indicated that the point B is
higher than the point A, while if it was negative, then point B
is lower than the point A.

FACTORS AFFECTING THE MEASURING PROCEDURE OF

THE AUTOMATIC LEVEL

Every operation in a measurement procedure is a possible

error source and as such requires careful consideration in
order to assess the effect on the final result.

POINTING AND FOCUSING

Obviously the instrument will not work if it is not pointed at
the staff. The amount of staff that needs to be read depends
on the range of the instrument to the staff. However, there
will be a minimum amount necessary at short ranges. It may
not be critical to have the staff pointing directly at the
instrument. The precision of the height measurement may
be independent of sharpness of image; however, a clear,
sharply focused image reduces the time required for the
measurement. If the image is too far out of focus then the
instrument may not read at all. Some instruments have an
auto-focus function to avoid potential focusing problems.

VIBRATIONS AND HEAT SHIMMER

Vibration of the compensator caused by wind, traffic, etc.,
has a similar effect on the bar code image as that of heat
shimmer. However, as digital leveling does not require a
single reading, but instead is dependent on a section of the
code, the effects of shimmer and vibration may not be
critical. Similarly, scale errors on the staff are averaged.

ILLUMINATION
As the method relies on reflected light from the white
intervals of the bar code, illumination of the staff is
important. During the day, this illumination will be affected
by cloud, sun, twilight and the effects of shadows. Up to a
point these variations are catered for by the instrument but
under adverse conditions there may be an increase in the
measuring time.

STAFF COVERAGE
In some conditions part of the bar code section being
interrogated by the instrument may be obscured.

Consult the manufacturer’s handbook to ensure that

sufficient of the staff is showing to the instrument.
COLLIMATION
The collimation value is set in the instrument but can be
checked and changed as required. The method of
determining the collimation is based upon one of the two
peg methods described earlier. Once the collimation value
has been determined it is applied to subsequent readings
thereby minimizing its effect. Note, however, that it can
never be completely removed and appropriate procedures
according to the precision required must still be applied.

PHYSICAL DAMAGE
It is likely that the instrument will be seriously damaged if it
is pointed directly at the sun.

MISTAKES
 Improper use of a long rod
 Holding the rod in a different place for the back and fore
sight on a turning point
 Waving a Flat bottom Rod while holding it on a flat
surface
 Reading a foot too high
 Recording notes
 Touching tripods or instrument during reading process

REDUCING ERRORS AND ELIMINATING MISTAKES

The following routines prevent most large errors or quickly
disclose mistakes
 Checking the bubble before and after each reading
 Using a rod level
 Keeping the horizontal lengths of back and foresights
equal
 Running lines backward and forward

From the knowledge of the possible sources of errors listed

above, the leveling process was carried out with caution and
consciousness of these sources. The result of this can be seen
from the accuracy of the leveling circuit computation and
height determination of each point.

CONCLUSION: SUMMARY AND RECOMMENDATION

 PROBLEM ENCOUNTERED
During the execution of the assignment, the following
problems were encountered.
1)The land was very hard which make it difficult to
bury pegs into the ground, the problem was
overcome by drilling the ground before burying the
pegs
2)Traffic congestion was another problem, due to
location of the site, the traffic disturbed. The problem
was later overcome by much patient.
 RECOMMENDATIONS
From the problem encountered, experience and knowledge
acquired during the execution of this assignment, we hereby
recommend the following
 1)More explanation should be given to the student on
the practical assignment.
2)Enough instrument should be given to students
Tutorial class should be given to student on the use of
AutoCAD software.

One of the recommendations of this lab work is the use of a

digital level in place of an automatic level.
In the course of the leveling work it was discovered that for
a good degree of accuracy i.e. reduced final error, then the
readings should be taken to 3 decimal places.
The leveling and traversing operation from Afe Babalola to
Faculty of Art was done using level, leveling staff, tape and
ranging poles. The procedure started from reconnaissance
then test of instrument, control check data acquisition, data
processing and data presentation. The report write up was
the final stage where everything done was reported.
After the precautions have been taken for the field
observation, deduction, processing and presentation of data,
the aim of this practical was achieved most especially, the
skills, knowledge, experience and strategy needed for the
execution of leveling and traversing operation. Finally the
end product of the survey operation was submitted to the
lecturer in charge in form of hard copy and soft copy.
REFERENCE
Elementary Surveying- An introduction to Geomatics by
Charles D. Ghilanni and Paul F. Wolf