Lecture 15 Compass Surveying

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What is the primary purpose of compass surveys?

To quickly fill in details in larger surveys (correct)

To ensure there are no magnetic disturbances present

To precisely determine the bearing of a line

To provide highly accurate measurements of distances

Why is chain survey preferred in small areas requiring high accuracy?

It is not affected by magnetic disturbances

It is faster than compass survey

It provides more accurate measurements of direction (correct)

It aligns the needle to a constant reference point

What is a major limitation of compass surveys in determining line bearings?

Constant exposure to magnetic disturbances

Inaccuracy in distance measurements

Constant alignment to a reference point

Alignment to the earth's magnetic field (correct)

Why is it important to ensure magnetic disturbances are not present during compass surveys?

To avoid affecting the alignment of the compass needle Signup and view all the answers

Which type of compass survey is usually carried out on a large area?

Prismatic compass survey Signup and view all the answers

Why are compass surveys mainly used for explanatory works?

To offer rapid detail filling in larger surveys Signup and view all the answers

What is the main purpose of a surveyor's compass?

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

In the context of back and fore bearings, what is the back bearing?

The bearing between two successive stations in opposite directions Signup and view all the answers

If a forward bearing is given as 100°, what would be the corresponding back bearing?

280° Signup and view all the answers

What is the general rule for determining back bearing from a forward bearing?

Add 180° if forward bearing is less than 180°, subtract 180° if greater Signup and view all the answers

What is the purpose of taking a back bearing when traversing with a compass survey?

To check the accuracy of the compass readings Signup and view all the answers

What is the difference between whole circle bearing system (W.C.B) and reduced bearing (R.B)?

W.C.B measures angles up to 360ᴼ, R.B measures angles up to 90ᴼ Signup and view all the answers

In which system are survey line bearings measured with respect to the north or south line closest to them?

Quadrantal Bearing System (Q.B) Signup and view all the answers

What is the influence that prevents the magnetic needle from pointing to the magnetic north pole?

Local attraction Signup and view all the answers

How can local attraction be detected in compass surveying?

By checking the difference between forward bearings and back bearings of lines Signup and view all the answers

In compass surveying, what is the correction method applied if none of the lines have the correct difference between forward bearing and back bearing?

Balancing the line with the minimum error Signup and view all the answers

Which method of local attraction elimination in compass surveying is based on ensuring that the interior angles measured at affected stations are right?

Second method Signup and view all the answers

What is the primary purpose of levelling in surveying?

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

Which surface is defined as any surface parallel to the mean spheroid of the earth in levelling terminology?

Level surface Signup and view all the answers

In compass surveying, what should be satisfied before applying the graphical rule?

Geometric closure Signup and view all the answers

What does the transit rule in surveying emphasize regarding measurement precision?

Precise angle measurements over length measurements Signup and view all the answers

Which component of the prismatic compass is used to sight objects in line with the eye sight?

Object vane Signup and view all the answers

What is the main function of the prism in a prismatic compass?

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

In a prismatic compass, what role does the graduated circle or ring play?

Measures all possible bearings of lines Signup and view all the answers

What protects the prism hole in a prismatic compass from dust and moisture?

Prism cap Signup and view all the answers

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

Mirror on the forward vane Signup and view all the answers

What is the primary purpose of the cylindrical metal box in a prismatic compass?

Forms the entire casing of the compass Signup and view all the answers

Which part of the prismatic compass measures the angle of a line from the magnetic meridian?

Magnetic needle Signup and view all the answers

What does the lifting pin and lifting lever in a prismatic compass do?

Lifts the magnetic needle out of pivot point to prevent damage Signup and view all the answers

How does the surveyor's compass differ from the prismatic compass?

The surveyor's compass has a larger and more accurate design. Signup and view all the answers

What is carried on a mounting that can be moved up and down between slides fixed on the outside of a prismatic compass case?

Prism Signup and view all the answers

What method is used to determine the difference in elevations of two points in differential levelling?

Fly levelling Signup and view all the answers

In differential levelling, what adjustments are performed at temporary positions near the first point?

Setting up, levelling up, elimination of a par- allot Signup and view all the answers

Why might it be necessary to set up the instrument several times in differential levelling?

Due to the distance between points Signup and view all the answers

What is the purpose of taking back sight as a turning point in differential levelling?

To have both back sight and fore sight readings Signup and view all the answers

How are reduced levels calculated in differential levelling?

By rise and fall method Signup and view all the answers

What arithmetic check is performed in the process of differential levelling?

$ ext{B.S} - ext{F.S} = ext{Rise} - ext{Fall}$ Signup and view all the answers

What is the main purpose of internal focusing in a telescope?

To eliminate errors due to non-parallelism Signup and view all the answers

What is the primary function of back sight in levelling?

To establish the plane of collimation or sight Signup and view all the answers

What correction is applied to staff readings to make objects appear higher than their actual height?

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

What kind of levelling technique involves taking readings from temporary bench marks?

Fly levelling Signup and view all the answers

In profile levelling, what is the main purpose of drawing the sectional view of the ground?

To decide on construction routes Signup and view all the answers

What is the primary function of intermediate sight in levelling?

To take readings after back sights before shifting the instrument Signup and view all the answers

Which type of telescope performs focusing by externally moving the objective or eyepiece?

'External focusing telescope' Signup and view all the answers

'Reduced level' in levelling refers to:

'The level of a point with respect to an assumed datum' Signup and view all the answers

What is the purpose of the glass cover in a prismatic compass?

To protect the instrument box Signup and view all the answers

What is the main function of sun glasses in a prismatic compass?

To bisect luminous objects Signup and view all the answers

How is centering of a prismatic compass checked?

By dropping a pebble from under the compass Signup and view all the answers

What is the aim of leveling a prismatic compass?

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

What causes the largest variation in magnetic declination?

Secular Variation Signup and view all the answers

What is the magnetic bearing of a survey line?

Angle between survey line and magnetic meridian Signup and view all the answers

Why does the direction of a magnetic meridian not coincide with the true North pole?

Magnetic meridian follows Earth's magnetic field Signup and view all the answers

What is the role of reflecting mirror in a prismatic compass?

To get an image of an object located above or below instrument level Signup and view all the answers

What is meant by 'angle of declination' at any point?

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

What is the main purpose of a levelling staff?

To determine the height of various points above a datum Signup and view all the answers

Why is Mean Sea Level (MSL) used as a reference in surveys?

It represents the average height of the sea over time Signup and view all the answers

Which type of bench mark is G.T.S?

Permanent bench mark Signup and view all the answers

What differentiates a Dumpy level from a Wye level?

Dumpy level has simpler construction with fewer movable parts Signup and view all the answers

What is the purpose of a levelling head in a leveling instrument?

To bring the bubble in its center of run Signup and view all the answers

What is the fundamental axis of a level?

Vertical axis Signup and view all the answers

In what way does the Axis of Telescope differ from the Line of Collimation?

The Axis of Telescope joins the intersection of cross hairs and eyepiece, whereas Line of Collimation joins cross hairs and object glass center Signup and view all the answers

'Reduced level' in surveying refers to:

'Reduced' levels derived from averaging heights above a datum surface Signup and view all the answers