Compass Survey Quiz and Flashcards

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Questions and Answers

What is the primary purpose of compass surveys?

Filling in detail for large surveys quickly (correct)

Determining precise magnetic bearings

Surveying small areas with high accuracy

Providing extremely accurate measurements

When is chain surveying preferred over compass surveying?

When magnetic disturbances are present

For small areas

For larger areas

When high accuracy is required (correct)

What is a major limitation of compass surveys regarding bearing measurements?

Requires minimal calibration

Ensures precise angular measurements

Provides constant reference points

Aligns to the earth's magnetic field (correct)

Which type of compass is mainly used for magnetic bearing measurements?

Prismatic compass Signup and view all the answers

Why should care be taken when using a compass survey?

To eliminate magnetic disturbances Signup and view all the answers

What distinguishes a prismatic compass from other types of compasses?

It is small and portable Signup and view all the answers

What is local attraction in compass survey?

Magnetic influence caused by unavoidable substances like underground iron pipes Signup and view all the answers

What is the main difference between the Prismatic Compass and Surveyor's Compass?

Size and accuracy Signup and view all the answers

In which direction do the graduations on the prismatic compass run?

Clockwise from the south end of the needle Signup and view all the answers

How is local attraction detected in compass survey?

By checking the difference between the bearings of lines in a traverse Signup and view all the answers

What is the purpose of the 45º reflecting prism in the prismatic compass?

To magnify the image of the graduations Signup and view all the answers

Which method is based on the fact that the interior angle measured on an affected station should be right?

Second method of local attraction elimination Signup and view all the answers

Which part of the prismatic compass is used for solar observations and viewing high objects?

Mirror in front of the forward vane Signup and view all the answers

What is a level surface in levelling?

A surface parallel to the earth's mean spheroid Signup and view all the answers

What is the main purpose of levelling?

To determine the elevation of points above or below a datum line Signup and view all the answers

What protects the prism hole in the prismatic compass?

Prism cap Signup and view all the answers

What does the eye vane in the prismatic compass have at its bottom?

Eye hole Signup and view all the answers

Which substance does NOT fall under local attraction in compass survey?

Instrument used for measurement Signup and view all the answers

What part of the prismatic compass is used to sight an object in line with eyesight?

Object vane Signup and view all the answers

How are errors detected in a closed traverse?

By comparing the sum of interior angles to a specific formula Signup and view all the answers

What is placed exactly opposite to the object vane in the prismatic compass?

Prism Signup and view all the answers

What protects the compass from dust, rain, etc.?

Cylindrical metal box Signup and view all the answers

What measures all possible bearings of lines on a prismatic compass?

Graduated circle or ring Signup and view all the answers

What is the average height of the sea of all stages of tides known as?

Mean sea level (MSL) Signup and view all the answers

Which line is at right angles to the plumb line?

Horizontal line Signup and view all the answers

What is the point or surface with respect to which levels of other points or planes are calculated called?

Datum Signup and view all the answers

What type of benchmark is a relatively permanent point of reference?

Permanent bench mark Signup and view all the answers

Which part of the level instrument provides the horizontal line of sight?

Telescope Signup and view all the answers

What is the modern form of dumpy level that has the telescope tube and the vertical spindle cast as one piece?

'Solid dumpy' Signup and view all the answers

'Tribrach' is the upper part of what component in a leveling instrument?

'Levelling head' Signup and view all the answers

'Target staff' and 'Self-reading staff' are types of what tool used in leveling?

'Levelling staff' Signup and view all the answers

'Vertical axis' in a level instrument is defined as what?

'Centre line of axis of notation' Signup and view all the answers

'Setting up', 'Levelling up', and 'Focusing' are steps involved in what temporary adjustment of a level instrument?

Instrumental adjustment Signup and view all the answers

What is the purpose of using sun glasses in a prismatic compass?

To bisect luminous objects Signup and view all the answers

How is centering checked when using a prismatic compass?

By dropping a small pebble from the underside of the compass Signup and view all the answers

What is the purpose of levelling in a prismatic compass operation?

To allow the graduated circular ring to swing freely Signup and view all the answers

What is Secular Variation in relation to magnetic declination?

A continuous slow change with a cycle of 400-500 years Signup and view all the answers

How does Diurnal Variation affect magnetic declination?

By changing continuously over short periods Signup and view all the answers

What does 'Magnetic Bearing' refer to in surveying?

The angle between a survey line and the magnetic meridian Signup and view all the answers

What is Magnetic Meridian at any place defined as?

The direction obtained by observing a freely supported magnetized needle Signup and view all the answers

What causes Irregular Variations in magnetic declination?

Sudden variations due to magnetic storms Signup and view all the answers

How often does Periodic Variation occur in magnetic declination?

Every eleven years Signup and view all the answers

What is Angle of Declination with respect to magnetic meridian?

Angle between magnetic meridian and true meridian Signup and view all the answers

What is the purpose of a surveyor's compass?

Determining the magnetic bearing of a given line Signup and view all the answers

What is the difference between fore bearing and back bearing?

Fore bearing is the initial direction, and back bearing is the opposite direction Signup and view all the answers

In which direction are bearings measured from with respect to the observer?

North Signup and view all the answers

What happens if the fore bearing is less than 180 degrees?

180 degrees are added to get the back bearing Signup and view all the answers

How are bearings designated in the Whole Circle Bearing System?

Measured in a clockwise direction with respect to the magnetic meridian Signup and view all the answers

What is Reduced Bearing (R.B) in surveying?

A method of converting whole circle bearings to quadrantal bearings Signup and view all the answers

'Back Bearing BA = Forward Bearing AB - 1800' indicates that:

'Back Bearing' is always greater than 'Forward Bearing' Signup and view all the answers

'Traversing with the compass' involves:

Taking bearings along straight lines and measuring distances simultaneously Signup and view all the answers

'Choosing a suitable scale' in surveying refers to:

'Suitable scale' for plotting the traverse considering the area's shape Signup and view all the answers

What is the main purpose of focusing in a telescope?

To bring the image to the plane of cross hairs Signup and view all the answers

In which type of telescope is the focusing done externally?

External focusing telescope Signup and view all the answers

What is the error in measurement due to non-parallelism in a bubble tube called?

Sensitivity error Signup and view all the answers

What correction is applied to staff readings to make objects appear higher than they really are?

$CR = 0.01121d^2$ Signup and view all the answers

What is the height of instrument in levelling defined as?

Elevation of the level plane respect to assumed data Signup and view all the answers

What is the purpose of taking a back sight in levelling?

To determine plane of collimation Signup and view all the answers

'Reduced level' in levelling refers to:

Level of a point with respect to assumed datum Signup and view all the answers

'Fly levelling' is primarily used for:

Levelling with respect to temporary benchmarks Signup and view all the answers

What type of levelling is used when the distance between two points is very large?

Differential levelling Signup and view all the answers

What does 'profile levelling' involve?

Drawing the sectional view of the ground based on reduced levels Signup and view all the answers

What is the main consideration when engineers decide the formation level of a proposed project?

Minimizing the transport of earth Signup and view all the answers

What is another name for 'Differential Levelling'?

Direct Levelling Signup and view all the answers

What does a 'Turning Point' have during the levelling process?

Back sight and intermediate sight readings Signup and view all the answers

What method can be used to calculate Reduced Levels during levelling?

Height of Instrument method Signup and view all the answers

When points in levelling are distant from each other, why might the instrument need to be set up several times?

To ensure accuracy in height measurement Signup and view all the answers

What is the purpose of performing temporary adjustments during the levelling process?

To ensure accurate readings and eliminate errors Signup and view all the answers

Study Notes

Compass Surveys

Primarily used for measuring angles and distances to plot land and features.
Chain surveying preferred over compass surveying in flat or small areas where greater accuracy is needed.
Major limitation: compass surveys can be affected by local magnetic anomalies, affecting bearing measurements.
Magnetic compass used mainly for magnetic bearing measurements.

Considerations in Compass Surveys

Care is needed to avoid local attraction, which can skew readings.
Prismatic compass distinguished by its design allowing easier reading through a prism, unlike other types.
Local attraction refers to disturbance in magnetic fields caused by nearby ferromagnetic materials.

Compass Instruments

Prismatic compass features a level, horizontal sighting for accuracy.
Graduations on the prismatic compass run from 0° to 360° clockwise.
Local attraction detected by comparing observed bearings with known values.

Optical Components

The 45° reflecting prism allows easy viewing of bearings without changing the compass's orientation.
Eye vane at the bottom provides additional sighting capability.
The prismatic compass is protected from dust and elements by a top cover.

Surveying Techniques

Errors detected in closed traverses by comparing the sum of angles or bearings.
Object vane is opposite to the sighting or eye vane for precise alignment.
Compass measures all possible bearings with a circle scale.

Levelling Concepts

Level surface defined as an imaginary plane where all points are at the same elevation.
Main purpose of levelling: to determine the elevation of points relative to a reference point.
A benchmark is a fixed reference used for elevation measurement.

Instrumentation in Levelling

Level instrument's horizontal line of sight provided by the telescope feature.
Modern dumpy level combines telescope tube and spindle as one unit for stability.
'Tribrach' refers to the upper part of a leveling instrument, aiding in setup.

Staff Types and Adjustment Procedures

Target staff and self-reading staff are tools used for establishing reading points during levelling.
'Vertical axis' refers to the central pivot around which the instrument rotates.
Steps for temporary adjustment include setting up, levelling up, and focusing to ensure accuracy.

Compass and Magnetic Variations

Sunglasses protect eyes from glare while using a prismatic compass outdoors.
Centering checked through observation of fixed reference points.
Secular Variation: long-term change in magnetic declination.

Magnetic Characteristics

Diurnal Variation affects magnetic declination based on daily solar activity.
Magnetic bearing relates to an object's direction concerning magnetic north.
Magnetic meridian defined as a vertical plane containing magnetic north and south.

Bearings and Their Designations

Fore bearing measures direction from the observer, while back bearing is the opposite.
Bearings measured clockwise from the north.
If fore bearing < 180°, it indicates a direction in the southwest quadrant.

Bearing Designation Systems

Whole Circle Bearing System designates bearings as a clockwise angle from the north.
Reduced Bearing (R.B) expresses direction in terms of the nearest cardinal direction (N/S, E/W).
Back Bearing (BA) calculated as Fore Bearing (AB) - 180° for opposite direction indication.

Telescope Focus and Errors

Focusing in a telescope improves clarity and precision of sighting.
External focusing performed in some telescope types for ease of adjustment.
Error due to non-parallelism in a bubble tube called collimation error.

Adjustments in Levelling

Height of instrument defined as the distance from the instrument to the ground level.
Back sight taken to establish a reference point for elevation.
'Reduced level' refers to the elevation of a point relative to a reference level.

Levelling Techniques and Applications

'Fly levelling' used for quick elevation checks over long distances.
Profile levelling involves mapping changes in elevation along a length.
Engineers consider ground conditions when determining formation level for projects.

Additional Levelling Concepts

Differential Levelling is another term for regular levelling methods.
'Turning Point' marks a location where measurements shift during levelling.
Calculation methods for reduced levels include height differences and reference checks.

Instrument Setup in Levelling

Instrument setup may be repeated if points are distant to maintain accuracy.
Temporary adjustments confirm the instrument’s alignment for precise measurements.

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Description

Learn about compass surveying, including its meaning, types, and the concept of bearing. This quiz covers the basics of using a compass for surveying purposes.

Compass Surveying: Introduction and Types

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