All you should Know about Surveying and Its Classification

 

Here is everything you need to know about surveying and its different classifications.

Surveying is a fundamental element of civil engineering since it is the initial stage in initiating a new civil engineering project.
A student must master the fundamentals of surveying in order to fully understand the procedures.
To begin learning surveying, one must first understand what surveying is and why it is important.

So first of all :

What is surveying ?

Surveying is simply the process of using direct or indirect measurements to determine the relative positions of various features on, above, or beneath the earth’s surface, and then putting them on a sheet of paper known as a plan or map.

Surveying skills are helpful in various of engineering processes. Any engineering project necessitates the use of surveying.
Below are some of the most important aspects of surveying.

You’re just about to know why surveying is that important , keep reading :

Why is it important ?

The first phase in surveying is to draw out a plan and a portion of the region that will be surveyed.
Based on the nature of the project, the best potential alignment, quantity of earthwork, and other relevant information can be computed using these prepared maps and sections.

Surveying measurements are used in the planning and design of all Civil Engineering projects, including railways, highways, tunneling, irrigation, dams, reservoirs, waterworks, sewage works, airfields, ports, enormous structures, and so on.

So, to conclude, any project of any size is built along the lines and points specified by surveying during its implementation as an initiation to its success and full achievement in the best possible ways.

 

Surveying most common classifications:

 

In order to get more in depth with surveying, you need to know that its most common classifications are:

• Plane surveying
• Geodetic surveying.

Let’s start with the first one :

Plane surveying :

Plane surveying refers to surveying in which the earth’s mean surface is treated as a plane and the spheroidal shape is ignored.
Plane triangles include all triangles created by survey lines. All plumb lines are parallel and the level line is deemed straight.
We are only concerned with a small portion of the earth’s surface in everyday life, and the above assumptions appear reasonable in light of the fact that the length of an arc 12 kilometers long lying on the earth’s surface is only 1cm greater than the subtended chord, and that the difference between the sum of the angles in a plane triangle and the sum of those in a spherical triangle is only one degree.

And that was all you need to know about plane surveying for now.
Now, let’s jump into the second type of surveying which is « the geodetic surveying ».

Geodetic surveying :

 

Geodetic surveying the second method of surveying that takes into consideration the shape
of the earth.
The lines on the surface are all curved, and the triangles are all spherical.
As a result, spherical trigonometry is required to be able to master the different phases of
this kind of surveying.
All geodetic surveys entail labor at a bigger scale and with a high level of precision.
We can say that the goal of a geodetic survey is to identify the precise location on the earth’s surface of a set of widely separated sites that serve as control stations for less precise surveys.

To conclude, there are two types of surveying : the plane surveying and the geodetic one.
As a matter a fact, it’s up to the civil engineer to choose the best type based on each project he’s asked to accomplish.

The question now is :

Are there other ways to classify surveying ?

The answer is a massive YES and you’re about to discover some other ways of classifying surveying.

 

Classification based on nature of field:

There are three categories of surveying that are classified depending on the nature of the field:

• Land surveying : which is divided into three categories: topographical survey, cadastral survey, and city survey.
  It is concerned with natural and man-made characteristics on land such as rivers, streams, lakes, wood, hills, highways, trains, canals, towns, water supply systems, buildings and properties, and so on.
• Marine surveying : This classification of surveying is also known under the name of hydrographic surveying, is simply the species and elements related to the water for the purposes of navigation, water supply, harbor construction, and mean sea level determination.
  Measurement of stream discharge, topographic survey of coasts and banks, taking and locating soundings to establish water depth, and recording ocean tidal fluctuations are actually all part of the job we’re talking about.
• Astronomical Surveying: This type of surveying allows a surveyor to determine the absolute location of any point on the earth’s surface, as well as the absolute location and direction of any line.
  This entails making observations of celestial bodies like the sun or any fixed star. (this one is quite interesting).

 

Classification based on instruments used :

Surveying can be split into six groups based on the different types of instruments employed :

• Surveying in a chain
• Surveying using a compass
• Surveying on a plane table
• Surveying using a theodolite
• Tacheometric surveying is a method of measuring the distance between two points.
• Surveying using photographs

Methods used for classification: Or in other words, classification based on the method used .
Surveying can be classified into the following categories based on the methodologies used:

 

• Surveying via triangulation
• Surveying in a straight line

And … the last surveying classification , and my favorite one is :
Object-based classification:
There are four different forms of surveying based on the object:

• Surveying of the Earth
• Surveying of Mines
• Surveying archaeology
• Military reconnaissance

What is Compass Surveying

 

 

INTRODUCTION

Compass surveying is the branch of surveying in which directions of survey lines are determined with compass and the lengths of the lines are measured with a tape or a chain. In compass surveying the direction of survey line called the bearing of line is defined as the angle made by the line with the magnetic meridian. In practice compass is generally employed to run a traverse. Traverse consists of series of straight lines connected together to form an open or closed traverse.

COMPASS

The commonly used instrument for compass surveying is Compass. A compass is small instrument which consists essentially of magnetic needle, a graduated circle and a line of sight. When the line of sight is directed towards a line, the magnetic needle points towards magnetic meridian and the angle which the line makes with the magnetic meridian is read at the graduated circle.

Compass consists of cylindrical metal box of about 8-12 cm diameter in the center of which is a pivot carrying a magnetic needle which is already attached to the graduated aluminum ring. The ring is graduated and is read by reflecting prism. Diametrically opposite to the prism is the object vane hinged to the box side carrying a horse hair with which the object in the field is bisected.

TYPES OF COMPASS

There are two forms of compass as under

1. Prismatic compass
2. Surveyors compass

The two compass are almost same except few differences so far as their construction is concerned. Prismatic compass uses WCB (0⁰­­-360⁰) circular ring while as the surveyors compass uses Quadrantal Bearing (0⁰­­-90⁰) circular ring system. Besides bearing system, the former has graduated ring attached to magnetic needle as the result of which when compass box and sight vane is rotated the needle remains stationary on the other hand in surveyors compass graduated ring being attached to compass box moves with it as the box is rotated

 

ADJUSTMENT OF COMPASS (WORKING)

Working of compass involves three steps:

1. CENTERING
2. LEVELLING
3. OBSERVING THE BEARING

Centering involves to align the compass is such a way the Centre is placed vertically over the station point. It is done with the help of tripod stand and is checked by dropping a small pebble below the Centre of compass.

Levelling is done so that the graduated ring swings quite freely. It is done with the help of ball and socket arrangement and can be checked by rolling a round-pencil on the compass box

Observing the bearing once centering and levelling has been done, raise or lower the prism until the graduations on the ring are clearly visible when looked through the prism. Afterwards turn compass-box until the ranging rod at the station is bisected by horse-hair of objective vane. At this position note down the reading.

COMPASS TRAVERSING

Whenever in traversing compass is used for making angular measurements, it is known as compass traversing or compass surveying. In compass traversing, the compass is used to determine the direction of survey lines of the framework of the traverse for measuring the angles which these lines make with the magnetic meridian.

The process of chaining and offsetting is the same as in chain surveying and running the check lines is not necessary. Compass traverse may be closed or open. Close traverse starts from one traverse station and closes either on same or on another traverse station whose location is already known. On the other hand an open traverse starts from one station and closes at other station whose location is neither known nor established.

 

EQUIPMENT USED IN COMPASS SURVEYING

• PRISMATIC COMPASS
• MEASURING TAPE
• RANGING RODS
• PLUMB BOB
• CHAIN
• CROSS STAFF

 

MEASUREMENT OF INCLUDED ANGLE

In a compass (prismatic) which uses Whole Circle Bearing (0⁰ to 360⁰) system the included angle is given by

Included angle   =  F.B of next line  —  B.B of previous line at same station

 

PRECAUTIONS

Compass surveying is used in case of rough surveys where speed and not accuracy is main consideration. One of the biggest disadvantages of compass is that magnetic needle which gives bearing of lines is disturbed from its normal position in presence of materials such as iron-pipes , current carrying wires , proximity of steel structures , transmission lines etc. called sources of local attraction.