4.0: ELEMENTARY SURVEYING AND MAP- Form three topic
4.0: ELEMENTARY SURVEYING AND MAP
4.1: meaning and types of survey
Concepts from this subtopic
a. Meaning of simple land survey
b. Types of simple land survey
Land survey refers to the art, science and technology of measuring and recording distance, angles, directions and elevation in order to position features on the earth surface relatively to other features.
Types of land survey
Criteria used to classify survey can include survey purpose, survey equipment used, survey method adopted and size of area to be surveyed.
In this lesson you will base only types of survey according to equipment which includes chain or tape survey, plain table survey, prismatic compass survey and land leveling.
4.2: Chain or tape survey
Concepts from this subtopic
a. Describe chain or tape survey
b. Types of equipment used in chain or tape survey
c. Practice chain survey activities at school level.
Chain or tape survey
Is surveying method whereby linear measurements are taken.
Equipment used in chain survey
(i) A chain
- It used to measure short straight distance.
- It is made up of tempered steel wire
- It has length ranging from 20 to 40 metres
- It is made of steel or synthetic material
- It has length of 20 to 100 metres
- It is used to measure a short distance
- It is made of wood or light aluminum metals.
- It has length about 2 to 3 metres long.
- It is used to mark temporarily points
- It has marked red and white or black to enhance visibility
- It is short piece of wood used to mark permanent position during survey.
- It has 40 mm square and 50cm long.
- It is made of wood or metal with eye slits at right angles
- It used to establish right angles on the ground perpendicular to survey line.
- It has length of 2 to 3 metres.
- They are made of still wire of 35- 40 centimeters long
- The steel wire normally bends at the top into a circle.
- Sometimes is tied up at cherty with red cloth to enhance visibility
- They are used to mark temporarily points.
- All observation and measurements should be recorded.
- Notebook should be spiral bound, good quality and 150× 100 mm in size.
- A hard pencil should be used for drawing and rubber for erasing errors.
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Chain or tape surveying process
It involves measuring of a series of short straight lines on the ground with a chain or tape measure to locate points with reference to the line of traverse by using tie lines or offset method.
(i) The line of traverse
- is a series of straight lines on the ground measured by chain or tape from fixed points.
-Actually, it is main line along which other lines (ties and offsets) are to be drawn.
(ii)Tie lines
- these are lines drawn from line of traverse at an angle between 30° and 60° to a fixed point in the field relatively to the line of traverse
- Tie lines join the line of traverse at acute angles or obtuse angles.
(ii) Offsets
- These are lateral measurements taken from an object to the chain line at right angles (90°)
- Objects or details recorded can be water tap, tree, building angle or pole.
A person who conducts survey activities is known as a surveyor.
Surveyor cannot work alone in the field to form a survey team. Mostly survey team is composed of three people who includes
(i) leader
(ii) The follower
(iii) The booker
(i) Leader
This is the one who initiates the movement along the line of traverse by holding the chain and arrows and moving forward.
(ii) The follower
-This is a member of survey team who puts the ranging pole, pags or arrows at the right point and hold the chain straight to the point.
- The follower is responsible in ranging as is directed by the leader.
-Ranging is establishing straight line between two points.
(iii) The booker
-This is a professional surveyor who works i the field as a recorder, sketcher and collector of all data obtained during surveying process.
Procedure in chain survey
(i) Reconnaissance
(ii) Observations and measurements
(iv) Presentation of survey data
(i) Reconnaissance
- It is first step in land survey.
- It is step involves visiting the area to be familiar with before actual survey is conducted.
- this step equips surveyors with a knowledge of topography and thereafter be able to determine types of equipment to be used and other resources.
- it involves determine the purpose or objectives of survey and preparing for site reconnaissance.
Before conducting a chain survey, there are several important factors to consider. Here are some key considerations:
1. Survey Purpose: Clearly define the purpose of the survey. Determine what information you are seeking to gather and how it aligns with your overall objectives. This will help you design the survey effectively.
2. Survey Scope: Determine the boundaries of the area you wish to survey. Consider the size, shape, and topography of the area, as well as any potential obstacles or challenges that may affect the survey process.
3. Equipment and Tools: Assess the necessary equipment and tools needed for the chain survey. This may include survey chains, ranging rods, tripods, compasses, theodolites, or total stations. Ensure that all equipment is in good working condition and properly calibrated.
4. Survey Team: Determine the size and composition of your survey team. Consider the required expertise and experience levels of the team members. Assign specific roles and responsibilities to each team member to ensure a smooth and efficient survey process.
5. Training and Familiarization: Make sure the survey team is adequately trained and familiar with the survey techniques and equipment being used. This will help ensure accurate measurements and minimize errors.
6. Survey Control Points: Identify and establish control points within the survey area. These points should be well-distributed and easily identifiable. They will serve as reference points for subsequent measurements and calculations.
7. Field Conditions: Assess the prevailing weather and environmental conditions that may impact the survey. Take into account factors such as temperature, wind, rain, and visibility. Plan the survey schedule accordingly to optimize data collection.
8. Safety Measures: Ensure that appropriate safety measures are in place for the survey team. This may include wearing safety vests, hard hats, and appropriate footwear. Identify potential hazards in the survey area and take necessary precautions.
9. Data Management: Plan how you will manage and store the survey data. Consider the required accuracy, precision, and format of the data. Determine if any GIS (Geographic Information System) or CAD (Computer-Aided Design) software will be used for data processing and analysis.
10. Legal and Ethical Considerations: Familiarize yourself with any legal or ethical considerations related to the survey, such as obtaining necessary permissions or permits, respecting privacy rights, and adhering to professional standards and guidelines.
11. Budget and Timeline: Develop a budget and timeline for the survey project. Consider the costs associated with equipment, personnel, data processing, and any other relevant factors. Create a realistic timeline that accounts for the survey duration, data processing, and reporting.
(ii) Observation and measurements
- It involves the process of taking measurements (booking), like distances between two points and determining right angles among others.
Procedure of measurement in chain survey
For example, determine the area of school farm
(a) Establish a base line AB from which all measurements are taken.
- A base line can be established along or across the farm where it is seen from all part clearly.
(b) Take a measurement at right angle (90°) from the chain line (baseline)
(c) Determine the area of each trapezium and rectangle obtained from measurements.
Booking in chain survey
Booking is process during which the measurements taken in the field and recoded in a field notebook. This is done by a surveyor.
The following should be taken into consideration during booking in chain survey to avoid unnecessary errors
(A) All linear measurements should appear at the center of the column and it has to start from the bottom upwards.
(B) Features at right hand side should be recorded on right hand side while those in left hand side should be recorded on left hand side of the column.
(C) All offsets and ties must be appearing on the side shown along survey line.
(iii)Presentation of survey data recorded
-survey can be presented in form of maps, plans or diagrams produced in a suitable scale
Procedure for adjusting elongated chain
i. Close up the joint s of the rings found to be opened out
ii. Reshape the damaged rings
iii. Romove one or more small rings
iv. Adjust the links at the end
Procedure for adjusting chain found to be too Short
i. Straighten the bent links
ii. Open the joints of the rings
iii. Replace small rings by bigger one
iv. Insert new rings where necessary
v. Adjust the links at the end
Advantages of chain survey
i. It does not involve complex mathematical calculation
ii. The equipment can be easily replaced
iii. It involves only few people
Disadvantages of chain survey
i. It cannot be conducted in large area
ii. It is only conducted in open ground areas.
iii. It is subjected with error
How to conduct chain survey accurately (avoid errors in chain survey)
i. Avoid establishing many survey lines
ii. Avoid setting main chain line along any obstacles
iii. Set major line from which other lines are developed
iv. All angles established triangles should range between 30° and 120°
v. Keep the chain line short and take accurate measurements
Obstacles in chain survey
Obstacles refers to any physical features or objects that obstruct the direct measurement of distance or angles between survey points. For example, rivers, building, tress and cliff.
Types of obstacles
i. obstacles which do not obscure visibility but obstruct chaining across it. For example, pond
ii. obstacle which obstructs chaining but not ranging poles. For example, river
iii. obstacles which obscure visibility and may not be walked through easily. For example, forest and mountain.
iv. obstacle obstructing both chaining and ranging
Techniques of overcoming obstacles in chain survey
a) Using right angle method
b) Using similar triangles
c) Using Pythagoras theorem
d) Using rectangle method
(a) Using the right angle method
It is applicable to those obstacles which do not obscure visibility but obstruct chaining across it. For example, pond.
I. Establish straight line of points AB
II. Insert ranging pole at C and F along survey line AB
III. From Point C and F establish a perpendicular line CD and FE at right angle to avoid the obstacle.
IV. From point D develop a line DE at right angle to avoid the obstacle
V. Thus, the distance of line DE=FC
(b) Using similar triangle technique
It is applicable to the obstacle which obstructs chaining but not ranging poles. Example is river
i.Establish a chain line AB
ii.Fix two poles at CD along AB on the side of the river
iii.At C develop perpendicular line CE such that an angle ACE is equal to 90°.
iv.Bisect line CE at O to make line DF so that CO=EO
v.Line CD=EF
(c) using Pythagoras theorem
-It used in obstacle such as building, forests or mountain
-It helps to overcome obstacles that obscure visibility
Pythagoras theorem is written as follows
(a²+b²= c²
Procedure:
Assume, the main line is AB
(i) Erect a ranging pole at point A;
(ii) From point A, develop a straight line to point C, such that point C is at right angle to point B where it avoids the obstacle
(iii) From point C develop a perpendicular line to point B, such that point A and B are in a straight line
(iv) Apply the Pythagoras Theorem to determine the distance of line AB.
Where:
CB=a
AC=b
AB=c
Formula (a2 +b2 = c2 )
(d) Using the rectangle method
This method is used to overcome any obstacle obstructing both chaining and ranging.
Suppose AB is a chain line.
(i) Two points A and B are aligned at one side of the building;
(ii) From both points A and B develop a perpendicular line, such that the developed line clears the object at A1 and B1 , respectively
(iii) Join points A1 and B1 , such that the line clears the obstacle to make point C
(iv) From point C develop a perpendicular line to point C1 , such that CC1 is the same distance as AA1
(v) From point C1 develop a straight line to point D, such that C1 D=AB
(vi) From point D, develop a straight line to point D1 such that CC1 =DD1 hence, BC1 =B1 C
Common errors in survey
Errors are discrepancies arising as a result of some fault and imperfection of instruments used or the human error.
a) Systematic errors (cumulative errors).
They are errors caused by expansion or contraction of steel band
b) Accidental errors (random errors or compensation). They are a result of lack of perfection of the human eye or in the methods and equipment used. They are errors which decrease with the increasing number of observations taken.
c) (c) Gross errors
This error is attributed by human incompetence and carelessness. For example, misplacement of a ranging pole, miscounting of bands or poor spelling of numbers in words.
Source of error in chain survey
i. Instrumental error. For example, bending of chain
ii. Human error. For example, eyes imperfection and incompetence
iii. Environmental error. For example, presence of obstacles and sunshine that cause expansion of chain.
Ways of avoiding errors or discrepancies in chain survey
i. Avoid steep slopes and major obstacles
ii. Involves measurement of short distance
iii. The chain should be checked and repaired before measurement.
iv. Verify the chain by using tape before measurement
v. The chain should not be allowed to bulge
vi. Allow reading and repetition of word during measurement
vii. To ensure accuracy recording of information.
NB: Now day there are development of survey technique takes a position of chain, plain table and compass survey that is called GPS (Global Position system).
GPS are advanced survey devices used to locate positions and measure distances between points, by utilizing satellite signals.
This instrument is used most because it collects more information quickly.
The importance of surveying in social and economic activities
i. It helps to prepare topographical maps which could show hills, valleys, rivers, villages, towns and forests of a region.
ii. It used for land use planning. An engineer’s map which shows features like irrigation canals, railways and roads is the work of survey.
iii. It can be used to prepare a contour map to determine the best possible route for roads and railways.
iv. Geological surveys produce maps which show underground resources. Surveys also can add details to existing plans on large scale maps.
v. It used for construction of buildings.
vi.
ACTIVITIES |
1. Students
should conduct a chain survey at school level to do the following activities (a) To measure any distance such as roads and school
ground (b) To measure any area of school environment (c) To solve various obstacles encountered during chain
survey (d) To determine errors and how to solve all errors |
Sample of questions
1. In a certain school students were tasked by the Sports master to construct a football pitch at Elohim Boys’ Secondary school that could be used during friendly match with a nearby school. The students decided to use surveying knowledge acquired in the classroom hence they opted for the use of leveling.
a. Describe five important instruments which could be used
b. Explain three procedures they followed during chain survey
2. Jacqueline and James are form three students from one among the schools here in Tanzania. They were ordered to draw lines of the playground using the knowledge they had from Geography.
(a) Explain any three instruments they were supposed to use
(b) Provide three pre-survey activities they had to do before the activity
(c) State the type of the simple land survey they had to use.
(d) What types of discrepancies might encounter them.
