Plane Table Surveying (Plane Table Survey)

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For 4th Semester Polytechnic CE Students
Written by Garima Kanwar | Blog: Rajasthan Polytechnic

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Subject: Advanced Surveying CE 4002(Same as CC 4002)

Branch: Civil Engineering 🏗️
Semester: 4th Semester 📚

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Plane Table Surveying (Plane Table Survey)

Plane Table Surveying is a simple, direct, and efficient method of surveying used in Civil Engineering to create maps and measure distances and angles in a small area. It involves drawing the map directly on the field using a plane table.

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1.1 Principles of Plane Table Survey

Plane Table Surveying is based on the principle of direct measurement. In this method, instead of recording data in the form of field notes, the surveyor directly sketches the features of the land onto a sheet of paper (called the plane table). The main components involved are:

• Plane Table: A flat surface on which the map is drawn.
• Alidade: A sighting device used to measure angles between the objects in the survey area and the table.

This method is ideal for smaller areas and where detailed measurements of the ground are needed.

Key Points:

• Direct drawing of features on the table.
• Measurement of angles and distances.
• Quick and accurate for small to medium areas.

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1.2 Accessories of Plane Table and Their Use

Here are the main accessories of a Plane Table and their functions:

1.2.1 Plane Table 📋

• Function: A flat surface on which the survey map is drawn.
• Material: Typically made of wood or a durable material.

1.2.2 Alidade 🔭

• Function: A sighting device used to measure the angles of objects in the survey area.
• Types:
  • Telescopic Alidade (a more precise version of Alidade with a telescope for better accuracy).
  • Simple Alidade (a ruler with sighting vanes).

1.2.3 Spirit Level 🔧

• Function: Used to ensure the table is perfectly horizontal.

1.2.4 Compass 🧭

• Function: Used to determine the magnetic bearings of lines.

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1.3 Setting of Plane Table

Setting up a Plane Table involves positioning the table on the ground and aligning it correctly to ensure accurate measurements.

1.3.1 Orientation of Plane Table 🌍

• Orientation means aligning the plane table in the right direction with the help of a compass or back sighting.
• Compass helps to determine the magnetic North and adjust the table accordingly.

1.3.2 Back Sighting and Magnetic Meridian Method 🔄🧭

• Back Sighting: It involves taking a sight from the table to a known reference point (like a fixed landmark) in the opposite direction.
• Magnetic Meridian Method: Using a magnetic compass to align the plane table with the Earth's magnetic North.

1.3.3 True Meridian Method 🌎

• The True Meridian Method involves aligning the table with the True North by using a solar observation or by a known reference point, usually based on maps.

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1.4 Methods of Plane Table Surveys

There are several methods for conducting a Plane Table Survey:

1.4.1 Radiation Method 🔴

• In the Radiation Method, the surveyor takes angular measurements from a central point (called the station or the table's position) to several visible objects or points in the area. These angles are plotted on the table.
• Example: When surveying a building, the surveyor takes measurements from a central point and radiates them outward to determine the building's outline.

1.4.2 Intersection Method ✂️

• In the Intersection Method, the surveyor measures the distance between the objects and the Plane Table. Two known points are sighted, and the point of intersection determines the position of the object.
• Example: If you want to find the position of a tree, the surveyor measures the angle from two different positions, and where the lines intersect, that’s where the tree is located.

1.4.3 Traversing Method 🔄

• The Traversing Method involves moving along a known path, measuring angles, and then plotting the points as you go. This method is useful for mapping long roads or boundaries.
• Example: Surveying the boundary of a plot of land by taking measurements at various points along the path.

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1.5 Merits and Demerits of Plane Table Survey

Merits of Plane Table Survey ✅

1. Simple and Quick ⏱️:

   • The method is easy to understand and execute.
   • Suitable for small areas with less complexity.

2. Direct Mapping 🖼️:

   • The surveyor draws the map directly, so there’s no need to record data and then transfer it to a map.

3. High Accuracy 🎯:

   • When properly set up and used, Plane Table Survey provides very accurate results.

4. Cost-Effective 💸:

   • Less expensive as it doesn’t require advanced equipment.

Demerits of Plane Table Survey ❌

1. Limited to Small Areas 🌍:

   • This method is best suited for small to medium-sized areas. Large areas can be difficult to manage.

2. Weather Dependency ☔:

   • The method is weather-dependent since the table and accessories need to be protected from rain or wind.

3. Skilled Surveyor Required 👷‍♂️:

   • It requires experienced surveyors to make accurate observations and map points correctly.

4. Difficult to Use in Rough Terrain ⛰️:

   • The method is less effective in hilly or uneven terrain where objects are not easily visible.

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Diagrams

1. Plane Table Setup
   • A flat surface is used to draw the map. The surveyor uses the alidade to sight the various points.

                     ________________________
                    |        Plane Table      |
                    |------------------------|
                    |                        |
                    |   Alidade (Sighting)   |
                    |                        |
                    |________________________|
                        (Surveying in process)

2. Radiation Method
   • The surveyor stands at a central station and measures angles to various objects.

              Object 1      Object 2
                   \        /
                    \      /
                     \    /
                      \  /
                     Central Station (Plane Table)

3. Intersection Method
   • Two known positions are used to sight objects. The intersection of the sight lines indicates the location of the object.

              Object
                |
       Sight 1 |  Sight 2
                |
     (Intersection Point)

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Question and Answer

Q1. What is the main principle of Plane Table Survey?
A1. The main principle of Plane Table Surveying is the direct measurement method, where survey data is plotted directly onto the plane table without the need for complex calculations.

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Q2. What are the three methods of Plane Table Survey?
A2. The three methods of Plane Table Survey are:

• Radiation Method
• Intersection Method
• Traversing Method

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Q3. What are the merits and demerits of Plane Table Survey?
A3.
Merits:

• Simple and quick
• Direct mapping
• High accuracy
• Cost-effective

Demerits:

• Limited to small areas
• Weather dependency
• Requires skilled surveyor
• Difficult in rough terrain

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Revision Points 🔑

1. Plane Table Survey is a simple and effective method for drawing maps directly on-site.
2. The main accessories are the Plane Table, Alidade, and Compass.
3. The three methods of Plane Table Surveying are Radiation, Intersection, and Traversing.
4. Merits: Direct mapping, high accuracy, cost-effective.
5. Demerits: Not suitable for large areas, weather-dependent, requires skilled surveyor.

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