What is Survey station, Base Line, Check Line, Offseft, Tie Line in Chain Survey?

 Principle of chain surveying

•    The principle of chain surveying is triangulation.
•    The total area is divided into small well-conditioned triangles.
•    Only linear measurements are there in chain surveying
•    No angular measurement

Chain Survey  Recommended:

•    The ground surface is more or less level.
•    For small areas.
•    A small-scale map is to be prepared.
•    The formation of well condition triangle is easy.

Important definitions in chain  Survey:

1. Survey Station 

In a chain survey, a station refers to a point where measurements are taken and recorded during the survey. It serves as a reference point for locating and measuring other points in the survey area. Stations are typically established at prominent features such as corners of buildings, intersections, or any other identifiable and easily accessible points. The chain survey stations help in creating a network of interconnected points that form the basis for mapping and analysis in the surveying process.

      There are three types of survey stations_

1. Main Station 
2. Subsidiary  Station 
3. Tie Station

        1. Main  Station:

•    Stations taken along the boundary.
•    The main survey station is denoted as shown in fig. with letters A, B, C etc
•    The line joining the main station is called the main survey line. 

        2. Subsidiary  Station:   

•   The station is on the main survey lines or any other survey line.
•   These subsidiary stations taken to run subsidiary lines for dividing the area into triangles.
•   For checking the accuracy and locating interior details.
•   it is denoted as shown in fig. with letters S1, S2, S3 

        3. Tie  Station:     

•   Also, subsidiary stations are taken on main survey lines.
•   The line joining the tie station is called the tie line.
•   Tie lines are mainly taken to fix the direction of adjacent sides of the chain survey map.
•   Also used to locate interior details and to form chain angles.
•   it is denoted as shown in fig. with letters T1, T2, T3

2. BaseLine

In chain surveying, the baseline refers to a measured line on the ground that serves as the initial reference for surveying other points or features in the area. It is a straight line segment of known length and acts as the fundamental reference for the surveying work.

The baseline is typically established by accurately measuring its length using a surveying chain or tape. This measurement serves as a basis for determining the distances and positions of other points in the survey. By measuring angles and distances from the endpoints of the baseline to other points, surveyors can create a network of interconnected measurements to map out the desired area.

The selection of a suitable baseline is crucial in chain surveying, as it should be relatively long, easily accessible, and have clear visibility between the endpoints. These considerations ensure that accurate measurements can be made from the baseline to other points, allowing for precise surveying and mapping of the area.

        Note  Point: : (Exam Point of View)

•    The line on which the framework of the survey is built is known as the base line.
•    The most important survey line.
•    The longest survey line.
•    Mostly taken over the fairly ground.
•    The magnetic bearings of the base line are taken to fix the north line of the map.

3. Check Line

In chain surveying, a check line is an additional line that is established to verify the accuracy of the survey measurements. It serves as a means of quality control to ensure the reliability of the survey results. 

The check line is typically measured independently of the main survey lines, using a different measurement method or equipment. It is used to cross-check the measurements obtained from the main survey lines and identify any potential errors or discrepancies.

The purpose of including a check line in a chain survey is to detect mistakes in linear measurements, angular measurements, or plotting. By comparing the measurements of the check line with the corresponding measurements obtained from the main survey lines, any inconsistencies or errors can be identified and corrected.

Including a check line in a chain, survey helps to increase the accuracy and reliability of the survey data. It provides a means of verifying the measurements and ensures that any errors or mistakes are identified and rectified before finalizing the survey results.

         

        Note  Point: : (Exam Point of View)    

• A line joining the apex point of the triangle to some fixed point of the baseline is known as a checking line.
• To check the accuracy of the triangle.
• Sometimes it helps to locate interior details.

4. Tie Line

In chain surveying, a tie line is a measured line that connects two points on the ground within a survey area. It is used to connect the main survey lines or traverse with nearby reference points or known control points.

The purpose of a tie line is to establish a connection between the main survey network and existing reference points, such as previously surveyed points or permanent markers. By measuring the tie line and determining its relative position to the reference points, surveyors can ensure the accuracy and consistency of their survey measurements.

Tie lines are particularly useful in chain surveying when there are obstacles, such as buildings, trees, or other obstructions, preventing a direct measurement between the main survey lines and the reference points. In such cases, a tie line can be established by measuring the distance and angles to intermediate points or by using other surveying techniques to connect the two points indirectly.

Tie lines help to maintain the accuracy and control of a survey by linking it to known reference points. They provide a means of tying the survey data to a reliable and established framework, ensuring the overall accuracy and reliability of the survey results.

5. Offset

In chain surveying, an offset line refers to a line that is perpendicular to a main survey line or baseline. It is used to measure or locate points or features that are situated at a certain distance from the main line.

The offset line is typically established by measuring the perpendicular distance from the main line to the desired point or feature. This can be done using a chain, tape measure, or other measuring instruments. The offset distance is measured at right angles to the main line, ensuring that the offset line is perpendicular to it.

Offset lines are commonly used in chain surveying for various purposes, including locating objects, determining boundaries, or mapping out features that are not directly on the main line. By measuring the offset distance from the main line, surveyors can accurately position and record the location of the desired points or features.

Offset lines can be used to create a detailed plan or map of an area by locating objects or features at specific distances from the main line. They provide a systematic way to measure and record the position of objects or features that may not be directly accessible or visible from the main line in a chain survey.

  Note  Point: : (Exam Point of View)    

•   The lateral measurement taken from an object to the chain line is known as Offset. (any angle)
•   Offsets are taken to locate objects with reference to the chain line.

Offset is two types

        i. Perpendicular Offset 

        ii. Oblique Offset

        i. Perpendicular Offset: Lateral Measurement is taken perpendicular to the chain line

        How to take perpendicular offset

• Swinging a tape over the chain line
• By using a ratio of 3:4:5
• By using builder’s square or tri-square
• By cross-staff or optical square

        ii. Oblique Offset: Lateral Measurement taken other than perpendicular to the chain line is called         oblique Offset

          Why Perpendicular offsets are preferred

• Easy to plotting
• Time-saving