Engineering Surveying Week 1

Question 1

What is engineering surveying?

Answer 1

• “Geomatics” which is the science and study of spatially related info

Question 2

What 6 activities does Geomatics cover?

Answer 2

1. Hydrographic surveying
2. Remote sensing
3. Cartography and visualisation
4. Photogrammetry
5. Geographic information systems (GIS)
6. Engineering surveying

Question 3

What are the 3 fundamentals of engineering surveying?

Answer 3

1. Heights
2. Distances
3. Angles

Question 4

What are the units for height, distance, and angle?

Answer 4

Height: mm or m
Distance: mm or m
Angle: Degrees, minute, seconds (d,m,s)

Question 5

How many minutes are in a degree?

Answer 5

60 ‘

Question 6

How many seconds are in a minute?

Answer 6

60 ‘’

Question 7

Convert 360 degrees to radians and gradians

Answer 7

• 2π
• 400^g

Question 8

What is 1 hectare in m²?

Answer 8

10000 m²

Question 9

What is the plane of collimation?

Answer 9

The horizontal plane used to read the staff in levelling

Question 10

What is a datum?

Answer 10

Known/assumed level to which the measured heights are referenced

Question 11

What is reduced level?

Answer 11

RL is the height of a point relative to the chosen datum

Question 12

What is the Ordinance datum?

Answer 12

Mean sea level at Newlyn Cornwall (Datum for Great Britain)

Question 13

What are the different types of bench marks?

Answer 13

• Temporary Bench Marks (TBMs)
• Transferred Bench Marks (TBMs)

Question 14

If a TBMs level is assumed, what type of bench mark is it?

Answer 14

Temporary bench mark

Question 15

If TBM is levelled from an OSBM or GNSS point what type of benchmark is it?

Answer 15

Transferred bench mark

Question 16

What is a HPC?

Answer 16

The height of the plane of collimation

Question 17

What is the level line?

Answer 17

One which at all points are normal to the direction of gravity as indicated by a plumb bob

Question 18

What is the horizontal line and how does it interact with the level line?

Answer 18

• One which is normal to the direction of gravity at one point only
• For distances up to 100m, these two lines are assumed to coincide

Question 19

What are the two types of optical level?

Answer 19

• Automatic level
• Digital level

Question 20

What are the similarities between the two types of optical levels?

Answer 20

• They each have a telescope
• They each have a levelling system

Question 21

What are the eight features of an automatic level?

Answer 21

1. Base plate
2. Foot screw
3. Pond bubble
4. Eyepiece (HAS CROSS HAIR)
5. Focusing screw
6. Tangent screw
7. Horizontal circle
8. Object lens

Question 22

What three elements does a levelling system have?

Answer 22

1. 3 footscrews
2. A pond bubble
3. A suspended compensator

Question 23

How do you eliminate parallax when levelling?

Answer 23

• Move eye up and down while looking into the eyepiece
• If the image does not appear to move there is no parallax

Question 24

Give all the information you know about the levelling staff?

Answer 24

• Telescopic - up to 5m, in several sections
• Graduated to 10mm
• Read by estimation to nearest 1mm
• To ensure the staff is vertical is should be “rocked.” The minimum reading will occur when the staff is vertical and this is the reading that should be taken

Question 25

What is the back sight (BS)?

Answer 25

* First reading taken after an instrument is setup * First BS must be to an OSBM or TBM

Question 26

What is a fore sight (FS)?

Answer 26

* Last reading taken before an instrument is moved * Last FS must be an OSBM or TBM

Question 27

What is an intermediate sight (IS)?

Answer 27

* Any reading which is not a BS or FS

Question 28

What is a change point (CP)?

Answer 28

* Staff position to which both a FS and BS are taken * A “CP” denotes a movement of the instrument

Question 29

What are the three sources of error in levelling?

Answer 29

1. Collimation error 2. Parallax: Image and X-hairs not focused properly 3. Staff and tripod defects

Question 30

What is collimation error and how is it detected?

Answer 30

* Caused by badly adjusted compensator * Detected using the “Two peg test”

Question 31

How do you calculate collimation error?

Answer 31

* Collimation error = True height difference - Apparent height difference * Where: * True height difference = S₁ - S₂ * Apparent height difference = S₃ - S₄ * Answer could be: * e = -0.004m per 60m (THE DISTANCE USED IS BIGGEST IN QUESTION) * e can be + or -

Question 32

How do you know if you need to adjust instrument for collimation error?

Answer 32

* If e ≤ 1mm per 20m, do not need to adjust * If e \> 1mm per 20m, you must adjust the instrument

Question 33

What are the other sources of errors in levelling?

Answer 33

* Field or On-Site errors * e.g staff not vertical, unstable ground, mishandling instruments, instrument not level, windy or hot conditions

Question 34

How do you calculate allowable misclosure?

Answer 34

5 \* n^½

Question 35

How do you calculate actual misclosure?

Answer 35

Calculated reduced level - Measured reduced level (IF THIS IS OUTSIDE ALLOWABLE MISCLOSURE, do not distribute error)