All questions of Geomatics Engineering (Surveying) for Civil Engineering (CE) Exam

Setting up a Plane Table

A plane table is an instrument used for surveying and mapping purposes. It consists of a flat table or board with a leveling head and a sighting device. To set up a plane table at any station, the following steps are followed:

1. Levelling and Centering:

The first step is to level and center the plane table. This is done by adjusting the screws on the leveling head until the bubble in the spirit level is centered. The table is then placed on the tripod and leveled in all directions using the leveling screws on the tripod.

2. Orientation:

Once the table is level, it is oriented to the true north using a compass or a theodolite. The table is then clamped in position.

3. Sighting:

The next step is to sight the target using the sighting device. The surveyor looks through the sighting device and lines it up with the target. The position of the target is then marked on the table using a pencil or a pin.

4. Sketching:

After the position of the target is marked, the surveyor sketches the surrounding details on the table. This is done by sighting and marking the position of several other targets and drawing lines between them.

5. Calculation:

Once the sketch is complete, the surveyor calculates the position of the targets and other features using trigonometry and other mathematical calculations.

In conclusion, leveling and centering are done simultaneously while setting up a plane table. This is to ensure that the table is stable and accurate while sighting and sketching the targets.

Given information:
Consecutive readings taken with a dumpy level and a 3 m staff on a continuous sloping ground: 0.425, 1.035, 1.950, 2.360, 2.950, 0.750, 1.565, 2.455.

To determine which readings are back sights.

Backsight:
A backsight is a reading taken on a point of known level or elevation, also known as a bench mark, which is used as a reference height for other readings.

Solution:
To determine which readings are back sights, we need to identify the points for which we have a known level or elevation. From the given readings, we can identify that:

- The initial reading of 0.425 is not a backsight as it is the starting point of the survey and there is no known level or elevation for this point.
- The reading of 2.950 is not a backsight as there is no indication that this point is a known level or elevation.
- The reading of 0.750 is a backsight as it is immediately followed by the reading of 1.565, which is higher. This indicates that the point with reading 0.750 is at a lower level or elevation and is a point of known height.
- The final reading of 2.455 is not a backsight as there is no indication that this point is a known level or elevation.

Therefore, the readings that are backsights are:
Option C: 0.425, 0.750.

Hence, option C is the correct answer.

**Explanation:**

The indirect method of contouring is a technique used in surveying to determine the shape of the land surface, particularly in areas with uneven terrain. It involves the use of contour lines, which connect points of equal elevation, to create a contour map.

The indirect method of contouring has several advantages over the direct method, which involves physically measuring the elevation at each point on the ground. These advantages include:

**1. Economy:**
- The indirect method is generally more economical than the direct method because it requires fewer field measurements.
- It relies on the interpolation of elevation values between known points, reducing the need for extensive field work.

**2. Suitability:**
- The indirect method is suitable for areas with complex terrain or limited access.
- It can be used in situations where it is difficult or impractical to measure the elevation at every point on the ground.

**3. Suitability for large projects:**
- The indirect method is particularly well-suited for large projects that cover a wide area.
- It allows for the efficient collection of elevation data over a large extent of land.

However, the indirect method of contouring does have one disadvantage compared to the direct method:

**4. Accuracy:**
- The indirect method may not be as accurate as the direct method because it relies on interpolation and estimation.
- It assumes that the elevation values between known points vary smoothly and continuously, which may not always be the case.
- In areas with abrupt changes in elevation or irregular topography, the indirect method may produce less accurate results.

Therefore, the correct answer is option 'C' - Accuracy. The indirect method of contouring does not have an advantage in terms of accuracy compared to the direct method.

Given data:
- Backsight reading on benchmark = 2.685 m
- Foresight reading on the point = 1.345 m
- Reduced level of benchmark = 500.00 m

We need to find the reduced level of the point.

Steps to find reduced level:

1. Calculate the height of instrument (HI):
- HI = Benchmark RL + Backsight reading
- HI = 500.00 m + 2.685 m
- HI = 502.685 m

2. Calculate the Reduced Level (RL) of the point:
- RL = HI - Foresight reading
- RL = 502.685 m - 1.345 m
- RL = 501.340 m

Therefore, the reduced level of the point is 501.340 m.

Hence, option (c) is the correct answer.

The included angle between the two lines is A, then the whole circle bearing of the new line formed by extending the preceding line by the included angle A is:

W3 = W1 + A - 180°

Note: This formula assumes that the angles are measured in degrees and that the bearings are given in the whole circle notation (i.e. from 0° to 360°).

Understanding Well-Conditioned Triangles
In civil engineering, the concept of well-conditioned triangles is critical for stability and structural integrity. A well-conditioned triangle ensures that calculations involving angles and lengths yield reliable results.
Defining Well-Conditioned Triangles
A well-conditioned triangle is typically characterized by having angles that are not too acute or too obtuse, which helps avoid computational errors in structural analysis.
Key Triangle Types
- Isosceles Triangle: This triangle has two equal sides and two equal angles. While it can be stable, the presence of two equal angles may lead to less predictable behavior under certain conditions.
- Equilateral Triangle: An equilateral triangle has all sides and angles equal (60 degrees each). This uniformity provides excellent structural properties and minimizes the risk of deformation or failure. It is considered the most stable configuration due to its symmetry.
- Right Angle Triangle: This triangle has one angle of 90 degrees. While useful in various applications, the presence of a right angle can sometimes lead to less favorable conditions for stability compared to equilateral triangles.
Conclusion
Given this analysis, the correct answer is option 'B', the Equilateral Triangle. It is the most appropriate well-conditioned triangle due to its uniformity in angles and sides, which enhances structural stability and predictability in calculations.
For civil engineering applications, choosing an equilateral triangle can significantly impact the reliability of structural designs and analyses.

Error due to Centering in Plane Table Survey

In plane table surveying, the process of centering involves setting up the plane table over a point on the ground from where the survey is to be conducted. It is essential to ensure that the table is accurately centered to minimize errors in the survey measurements. One such error is the misplacement of the station point, which can lead to inaccuracies in the plotted positions of the various survey points.

Significance of Scale in Plane Table Survey

The scale is an important aspect of a plane table survey as it determines the ratio between the distances on the map or drawing and the actual distances on the ground. It allows for the representation of large areas on a smaller piece of paper. The scale is usually expressed as a representative fraction (RF) or a graphic scale.

Error Due to Centering

The error due to centering in plane table surveying occurs when the station point is not accurately positioned on the ground. This misplacement can lead to the incorrect plotting of survey points and subsequent errors in the survey measurements. The error due to centering is dependent on various factors such as the accuracy of the centering process and the scale used in the survey.

Relation Between Error Due to Centering and Scale

The error due to centering should not exceed the scale divided by a certain factor. This factor represents the maximum allowable error due to centering, beyond which the accuracy of the survey may be compromised.

Calculation of Maximum Allowable Error

To calculate the maximum allowable error due to centering, the scale is divided by the factor specified in the question. In this case, the correct answer is option 'B,' which states that the error due to centering should not exceed the scale divided by 40.

For example, if the scale of the survey is 1:5000, the maximum allowable error due to centering would be 1/40 * 5000 = 125 units. This means that the misplacement of the station point should not exceed 125 units on the ground.

Importance of Limiting the Error Due to Centering

Limiting the error due to centering is crucial in achieving accurate survey measurements. Any misplacement of the station point can lead to cumulative errors in the plotted positions of the survey points. These errors can affect the overall reliability and precision of the survey data, leading to incorrect interpretations and decisions based on the survey results.

Conclusion

In plane table surveying, it is important to minimize the error due to centering to ensure the accuracy of the survey measurements. The maximum allowable error due to centering is determined by dividing the scale by a specified factor. Option 'B' in this question correctly states that the error due to centering should not exceed the scale divided by 40. By adhering to this criterion, surveyors can obtain reliable and precise survey data for various engineering and construction projects.

The horizontal angle between the true meridian and magnetic at a place is called declination.


- The Earth has a magnetic field that varies from place to place.
- The magnetic north pole and the geographic north pole are not located at the same point on the Earth's surface.
- The angle between the true meridian (geographic north) and the magnetic meridian (magnetic north) at a specific location is known as declination.


- The Earth's magnetic field is generated by the movement of molten iron in its outer core.
- This movement is influenced by various factors such as the rotation of the Earth and the interaction with the Sun's magnetic field.
- As a result, the magnetic field is not perfectly aligned with the Earth's rotational axis, leading to declination.


- Declination is measured in degrees east or west.
- If the magnetic meridian is to the east of the true meridian, the declination is positive (+).
- If the magnetic meridian is to the west of the true meridian, the declination is negative (-).


- Declination is an important parameter for navigation and surveying.
- It is used to convert magnetic bearings to true bearings and vice versa.
- Without considering declination, there can be errors in direction and positioning.


- Magnetic bearing: The direction of a line measured with respect to the magnetic meridian.
- Local attraction: Disturbances in a compass needle caused by nearby magnetic substances or structures.
- Azimuth: The horizontal angle measured clockwise from a reference direction, usually the north.

Therefore, the correct answer is option 'C' - Declination.

GIS (Geographic Information System) deals with spatial data.

Spatial Data:
Spatial data refers to data that is associated with a specific location or geographical area. It represents the physical features and characteristics of objects in the real world. Spatial data can include information such as coordinates, boundaries, distances, and relationships between objects.

GIS and Spatial Data:
GIS is a powerful tool that allows us to capture, store, manipulate, analyze, and visualize spatial data. It combines hardware, software, and data to create a digital representation of the real world. GIS enables users to view, understand, and interpret data in a geographic context.

Spatial data in GIS is typically represented using points, lines, or polygons. Points represent specific locations, such as the coordinates of a building or a landmark. Lines can represent roads, rivers, or boundaries, while polygons are used to represent areas such as land parcels, administrative boundaries, or land use zones.

Key Points:
- GIS deals with spatial data.
- Spatial data is associated with a specific location or geographical area.
- Spatial data represents the physical features and characteristics of objects in the real world.
- It includes information such as coordinates, boundaries, distances, and relationships between objects.
- GIS allows us to capture, store, manipulate, analyze, and visualize spatial data.
- Spatial data in GIS is represented using points, lines, or polygons.

In conclusion, GIS primarily deals with spatial data, which is essential for various applications such as urban planning, environmental management, transportation, and natural resource analysis. By leveraging spatial data and GIS technology, professionals can make informed decisions and gain valuable insights into the spatial relationships and patterns within their data.

When the whole circle bearing of a traverse line is between 90° and 180°, it means that the line is oriented in the southeast direction.

The correct statement is option C: The rise and fall method for the reduction of levels provided checks on all sights.

Explanation:
The rise and fall method is a commonly used method in surveying for determining the reduced levels of points. It involves taking readings of the staff at different points and applying corrections to account for errors and variations in the measurements. This method provides checks on all sights, ensuring the accuracy of the levelling process.

Here is a detailed explanation of the rise and fall method for the reduction of levels:

1. Procedure:
- The surveyor sets up the instrument at a known benchmark or reference point.
- The staff is placed at the desired points where readings are to be taken.
- The surveyor looks through the telescope of the instrument and reads the staff at each point.
- The readings are recorded, and corrections are applied to account for various factors.

2. Backsight and Foresight:
- The first reading taken on the staff is called the backsight. It is taken on a staff held at a point of known reduced level.
- The backsight reading helps to establish a starting point for the levelling process.
- The subsequent readings taken on the staff are called foresights. They are taken on staffs held at points whose reduced levels need to be determined.

3. Rise and Fall Calculation:
- After taking the backsight and foresights, the surveyor performs a calculation known as the "rise and fall" to determine the reduced levels of the foresight points.
- The rise and fall is the algebraic sum of the differences between each foresight reading and the preceding backsight reading.
- This calculation ensures that any errors or mistakes in the readings are identified and corrected.

4. Accuracy and Checks:
- The rise and fall method provides checks on all sights, which means that the accuracy of the levelling process can be verified.
- By comparing the calculated reduced levels of the foresight points with their actual known reduced levels (if available), the surveyor can check for any discrepancies or errors.
- This helps to ensure the reliability and accuracy of the levelling results.

In summary, the rise and fall method in levelling provides checks on all sights, allowing for the verification and correction of errors in the readings. This makes it a valuable and widely used method in surveying.