The principle of plane table survey is:

Question

Prepp Team · Accepted Answer

Understanding the Principle of Plane Table Survey

The question asks about the fundamental principle behind plane table surveying. Plane table surveying is a graphical method of surveying in which the field observations and plotting are done simultaneously.

The Core Principle: Parallelism

The main principle upon which plane table surveying works is Parallelism. This means that the rays drawn from the station point on the paper to the objects in the field are parallel to the lines from the station on the ground to the respective objects. To achieve this, the plane table is always oriented at each station such that the line representing the previous station on the paper is parallel to the line joining the current station and the previous station on the ground. This orientation is crucial for accurate plotting.

Let's break down how this parallelism is applied:

The plane table is set up at a station.
A point representing this station is marked on the drawing paper fixed on the table.
The table is oriented so that lines on the paper are parallel to corresponding lines on the ground.
Sights are taken to various objects using an alidade (a sighting rule), and lines are drawn from the station point on the paper along the alidade's edge towards the direction of the objects.
The distances to the objects are measured and scaled down to be marked on the lines drawn on the paper.

This process ensures that the relative positions of the objects plotted on the paper maintain the same angular relationship as the objects on the ground, due to the principle of parallelism.

Why Other Options Are Not the Primary Principle

While other concepts might be related to surveying or methods used *with* plane table surveying, they are not its core principle:

Traversing: Traversing is a surveying method involving a series of connected survey lines whose lengths and directions are measured. It can be performed using a plane table, but it is a method, not the principle.
Ranging: Ranging is the process of establishing intermediate points on a straight line between two terminal points. This is a basic operation in surveying, used in conjunction with various methods, but not the fundamental principle of the plane table.
Triangulation: Triangulation is a surveying method where a network of triangles is established to determine the positions of points. While observing angles (which relate to triangles) is part of sighting, the principle of plotting in plane table surveying relies on maintaining directional parallelism, not solely on forming and solving triangles for position determination.

Therefore, the fundamental principle governing plane table surveying is Parallelism.

Principle	Description in Plane Table Survey
Parallelism	Lines drawn on the paper from the station are parallel to the lines from the station on the ground to the objects. Achieved through proper orientation.

Revision Table: Key Principles in Surveying

Term	Brief Explanation
Plane Table Survey	A graphical method where field work and plotting are done simultaneously.
Parallelism	The core principle: Maintaining the paper's orientation so paper lines are parallel to ground lines.
Traversing	A survey method using a series of connected lines.
Ranging	Establishing intermediate points on a line.
Triangulation	Determining positions by forming networks of triangles.

Additional Information: Plane Table Surveying

Plane table surveying is relatively less precise than other methods like theodolite traversing but is quick and useful for small to medium-scale mapping, especially in detail plotting. The main equipment includes:

Plane Table: A drawing board mounted on a tripod, capable of rotation and leveling.
Alidade: A rule with sights, used for sighting objects and drawing lines on the paper.
Tripod: Supports the plane table.
Plumbing Fork and Plumb Bob: Used for centering the table over a ground station.
Trough Compass: Used for orienting the table to magnetic north, typically used for initial orientation or checking.
Spirit Level: Used for leveling the table.

Common methods used with plane table surveying include:

Radiation: Suitable for small areas. Station is set up, sights taken to points, and scaled distances are marked.
Intersection: Used when distances are hard to measure. Sights are taken to a point from two different stations; the point's position is where the lines intersect on the paper.
Traversing: Used for surveys along a line, like roads or rivers.
Resection: Used to determine the instrument station's position by taking sights to three or more known points.

All these methods rely on the fundamental principle of parallelism for accurate plotting.