3.Discussion
:

1.     
What is meant by surveying?

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Surveying is a technique of making all
the essential measurements for determining the relative position of points on
or beneath the Earth’s surface by measuring the horizontal distances,
elevations, directions, and angles. Surveying helps in analyzing and recording
all the characteristics of a terrain and designing
plans or maps for constructions such as bridges, highways, channels, dam, and pipelines. Surveys
will always be conducted to determine the location of the site and its
surrounding before the commencement of any engineering project. The aim of surveying is
typically used to obtain topographic information to prepare a map which shows the relative positions of the objects on the surface of the earth.

2.     
What are the principles of
surveying?

The fundamental
principles of surveying are :

       I.           
to work from the whole to the part.

    II.           
to locate a new station through linear
or angular measurements from fixed reference points.

According to the
first principle, the whole surveying area is first enclosed by forming a
network of control points (stations) with high precision. These points are
established by triangulation. The surveying area is then divided into numerous
large triangles with the greatest accuracy. These large triangles are further
divided into small triangles which are surveyed with less accuracy as figure 3.2.1. The objective of working from
the whole to the part is to control minor errors and to prevent the
accumulation of errors so that the aftermath of errors of one section does not
affect the rest.

Figure 3.2.1
 

 

 

 

 

 

 

According
to the second principle, after deciding the position of a new station, it can
be located by means of linear or angular measurement from at least two fixed
reference points. Linear measurement is actually horizontal distance which can be
measured by using tape. Angular measurement refers to the horizontal angle
which can be measured by using theodolite.

3.     
How many links are provided in a
20-meter metric chain?

Metric chains
come in many lengths such as 5, 10, 20 and 30 meters. However, the most
commonly used is 20-meter metric chain. Tallies are provided at every 2 meters
of the chain for easy reading of measurements. Every link of this type of chain
is 0.2 meters. Therefore, 100 links are provided in a 20-meter metric chain as
figure 3.3.1.

Figure 3.3.1
 

 

 

4.     
Differentiate between ranging rod
and offset rod.

Ranging rods and
offset rods are long poles that made up of wood and metal and painted with red
and white or black and white alternately as the figure
3.4.1. These rods are used to range some intermediate points in a survey
line and set out straight lines on the field when the survey line is long. The
only difference between ranging rod and offset rod is the length. Ranging rods
and offset rods are commonly 3 meters
long. Ranging rods of greater length than 3 meters are called ranging poles
that are used in a very long survey line, however,
the ranging poles are only available up to 8 meters long. Offset
rod has no flag attached to the top of it, but a flag with yellow or red or
white color will be attached to the top of a ranging pole for clear visibility
when the length of survey lines is long. Offset rod is typically used to measure
the offset of short lengths from the survey line and there are two narrow slits at right angles to each other which are used
to set right angles.

Figure 3.4.1
 

 

 

5.      Define
the terms baseline, tie line, and check line.

A baseline is the most significant and the longest
chain line which about passes through the center of the survey field as figure
3.5.1. This line will always be plotted first before the framework of triangles
are built on it. All the other measurements that show the details of the work
will be taken with respect this line. Therefore, the measurement of the
baseline must be accurate as the accuracy of the whole survey work depends on
it.

A tie line is a line
that joins some fixed points called stations to the main survey lines as figure 3.5.1. It helps to locate the
interior details and accuracy of surveying. The main objective of running a tie
line is to get the information of nearby objects.

A
check line is a line that connecting the
main station to a subsidiary station on the opposite site is connecting to the
subsidiary station as figure 3.5.1. Measurement of a check line will always be done to examine the accuracy of the
framework. The length of a check line
that is measured on the ground should be matched with its length on the plan.

 

Figure 3.5.1
 

 

Subsidiary Stations : F, G, H, L

 

Main Survey Stations : A,B,C,D,E
 

 

Main Survey Lines : AB, BC, CD, DE, EA

 

Base Line : BE

 

Check Lines : HL, MN

 

Tie Lines : AF, GC

 

 

 

 

 

6.      What
is meant by perpendicular and oblique offset?

Oblique offsets are measurements which are not made
at right angles to the survey line as figure 3.6.1. Perpendicular offsets are
measurements that are taken at right angle to the survey line as figure 3.6.1.

Figure 3.6.1
 

 

 

 

7.      What
is the usage of Total Station?

Total Station is an instrument that is integrated with distance measuring instrument
(EDM), angle measuring instrument (Theodolite),
and a microprocessor. It can be used to :

      
I.           
Measure elevations, coordinates, sloping
distance, horizontal and vertical angles in
tachometric, topographic and geodetic surveys. Measured data can be recorded in
the internal memory and transferred to the computer to further process for generating
a map of a surveyed area.

   
II.           
Record
excavations by archaeologists.

 III.           
Instantaneously
compute elevations, vertical and horizontal distance components, and
coordinates, and display on the LCD.

 IV.           
Store
data either in the internal data storage or the external data collector after measurements are taken.

   
V.           
Perform a variety of functions and computations such as :

·             
Averaging
multiple angle and distance measurements.

·             
Computing
horizontal and vertical distances.

·             
Corrections for temperature, atmospheric
pressure, and humidity.

·             
Calculating elevations of points from
the vertical distance components.

·             
Computing polars, inverses, and resections.

·             
Computing X, Y, and Z coordinates.

 VI.           
Measure the
elevation of objects from far away as figure 3.7.1, and known as Remote
Elevation Measuring (REM).

VII.           
Find the coordinate of missing pillars
using two known coordinates as figure
3.7.2.

VIII.           
Find its
coordinate using two control points as figure 3.7.3, and known as resection.

 IX.           
Calculate the area of a closed figure using
the coordinates of the corner of the figure as figure 3.7.4.

 

 

 

8.     
State the
advantages of works using Total Station?

x

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