A vertical line which is perpendicular to the level line is called:
Plumb line
Understanding Vertical and Level Lines in Surveying
In surveying, lines and surfaces are often defined based on their relationship to gravity and the Earth's shape. Key concepts include level lines, horizontal lines, and vertical lines.
What is a Level Line?
A level line is a line lying on a level surface. A level surface is perpendicular to the direction of gravity at all points. Imagine the surface of still water; that's a good approximation of a level surface. A line drawn on this surface would be a level line.
What is a Vertical Line?
A vertical line is a line that follows the direction of gravity. It points directly towards the center of the Earth (assuming a spherical Earth and uniform density for simplicity). A common tool used to establish a vertical line is a plumb bob hanging from a string.
Relationship Between Vertical and Level Lines
By definition, a level surface (and therefore a level line) is perpendicular to the direction of gravity at every point. A vertical line follows the direction of gravity. Therefore, a vertical line is always perpendicular to a level line at the point where they intersect.
This perpendicular relationship can be represented mathematically:
\( \text{Vertical Line} \perp \text{Level Line} \)
Analyzing the Options
Let's look at the provided options:
- Horizontal line: A horizontal line is straight and lies in a horizontal plane. A horizontal plane is tangential to the level surface at a point, and is perpendicular to the vertical line at that point. While a horizontal line is perpendicular to a vertical line, the question asks for a vertical line perpendicular to a level line. A horizontal line is not typically defined as a vertical line itself.
- Meridian line: A meridian line is a line representing true North-South. It lies in a vertical plane but is not the general term for any vertical line perpendicular to a level line.
- Plumb line: A plumb line is the line indicated by a string with a weight (plumb bob) at the end, hanging freely. This line follows the direction of gravity, making it a true vertical line. As discussed, a vertical line (like a plumb line) is perpendicular to a level line.
- Elevation line: This is not a standard term used to define a type of line in surveying related to verticality or levelness in this context. Elevation usually refers to the height of a point above a reference surface (like mean sea level).
Based on the definitions, the vertical line which is perpendicular to the level line is called a plumb line.
| Term | Description | Relationship to Level Line |
|---|---|---|
| Level Line | Line on a level surface, perpendicular to gravity. | Defines perpendicularity with vertical lines. |
| Vertical Line | Line following the direction of gravity. | Perpendicular to a level line. |
| Plumb Line | A specific type of vertical line defined by gravity. | Perpendicular to a level line. |
| Horizontal Line | Straight line tangential to a level surface at a point. Perpendicular to the vertical line at that point. | Not a vertical line; is perpendicular to a vertical line. |
| Meridian Line | Line representing true North-South, lies in a vertical plane. | A type of line in a vertical plane, but not the general term for a vertical line perpendicular to a level line. |
Conclusion on Plumb Line and Level Line
The question asks for a vertical line that is perpendicular to the level line. A plumb line is the definition of a vertical line in surveying, established by gravity. A level line is defined by being perpendicular to the direction of gravity. Therefore, a plumb line is the correct term.
Revision Table: Key Surveying Line Definitions
| Term | Definition |
|---|---|
| Plumb Line | Line following the direction of gravity (Vertical). |
| Level Line | Line lying on a level surface (perpendicular to gravity). |
| Horizontal Line | Straight line in a horizontal plane (tangential to level surface, perpendicular to vertical). |
| Vertical Plane | A plane containing a vertical line. |
| Horizontal Plane | A plane tangential to a level surface at a point (perpendicular to the vertical line at that point). |
Additional Information: Surveying Basics
Understanding the relationship between level, horizontal, and vertical lines is fundamental in surveying. These concepts are used to define elevations, establish bearings, and perform various measurements. While level and horizontal lines are often used interchangeably over short distances, it's important to remember their precise definitions:
- A level line is curved, following the curvature of the Earth.
- A horizontal line is straight and tangent to the level line at one point.
- A vertical line is always perpendicular to the level line, and also perpendicular to the horizontal line at the point of tangency.
The plumb line provides the essential vertical reference from which horizontal and level measurements are derived.
Important Questions from Levelling
The expression for sensitivity of the bubble tube (α) can be taken as, ______
Where n = No. of divisions, s = Net staff reading, D = Distance, R = Radius of curvature, l = Length of one division
In levelling between two points A and B on the opposite sides of a river, the level was first set up near A and the staff readings on A and B were 2.645 m and 2.30 m respectively. The level was then moved near B and set up; the respective staff readings then were 1.085 m and 1.665 m on A and B respectively. What is the true difference of level between A and B?
A level, when set up $20$ m from peg A and $70$ m from peg B, reads $0.750$ m on a staff held on A and $2.065$ m on a staff held on B, keeping the bubble at its centre while reading. If the reduced levels of A and B are $100.500$ m and $101.800$ m respectively, what is the collimation error per $100.0$ m?
In levelling back, sight is also called as ______.
A 'level line' is a-
