Engineering Surveying Week 2

Question 1

What are the three types of angles?

Answer 1

1. Horizontal
2. Vertical
3. Zenith

Question 2

What is a horizonal angle?

Answer 2

• Angle in the horizontal plane between vertical planes

Question 3

What is a vertical angle?

Answer 3

• Angle in the vertical plane from horizontal plane
• Angle above horizontal plane is angle of elevation
• Angle below the horizontal plane is angle of depression

Question 4

What is the zenith angle?

Answer 4

• Angle between vertical line above instrument and the line of sight
• Angle of elevation - 90° = Zenith Angle

Question 5

What equipment do we have for measuring angles?

Answer 5

• Total stations
• Theodolite (ANGLES ONLY)
• Targets (e.g nails in top of wooden pegs, special devices mounted on tripods, metal bars set in concrete)

Question 6

What can total stations do?

Answer 6

• Angle and distance measurements
• They measure horizontal and vertical angles and slope distances
• Large amounts of storage for data

Question 7

How do you select the right total station to measure angles depending on your tolerance?

Answer 7

• Every 1 “ is 0.5mm tolerance at a 100m sighting distance
• Hence if tolerance is 2mm and your working range is 100m you will need a 3” total station or better

Question 8

Learn this diagram on the principles of the total station

Answer 8

Question 9

What are the three axis on a total station?

Answer 9

Question 10

What are the two angle reading systems on a total station?

Answer 10

• Horizontal circle
• Vertical circle

Question 11

How do you level the total station in the horizontal plane?

Answer 11

• Use electronic level in conjunction with its footscrews

Question 12

How do you level the total station in the vertical plane?

Answer 12

• Done AUTOMATICALLY one the horizontal circle has been put into horizontal plane

Question 13

What are the 16 components of a total station?

Answer 13

1. Trivet (can be attached to a
   tripod)
2. Tribrach clamp (to
   detach/secure the total station
   to the trivet)
3. Tribrach
    carries the footscrews
    The tribrach may be
   detachable –useful when
   traversing (dealt with later in
   the module)
4. Battery compartment
   Power supply:
    Rechargeable battery.
    Can be Lithium-ion (Li-Ion),
   Nickle-cadmium (NiCd) or
   nickel metal hydride (NiMH)
   battery
    Comes with a spare – make
   sure both are fully charged.
5. Vertical tangent screw - (to
   move the telescope
   up/down)
6. Collimator - (to roughly
   sight/point to the target)
7. Carrying handle
8. Objective lens
9. Vertical circle
10. Horizontal tangent screw
11. Keyboard and LCD screen
12. Footscrew – for centring and
    levelling the instrument.
     there are 3 of these and they are
    used with the electronic level to
    set the horizontal circle in the
    horizontal plane
13. Circular bubble (pond bubble) 16
    – used to roughly level the
    instrument
14. Eyepiece (with cross-hairs on
    a diaphragm)
     Parallax must be eliminated
15. Image focus ring – to focus
    the image
16. Standards

Question 14

What does the microprocessor do on the total station?

Answer 14

• Performs multiple functions with main one calculating angles and distances

Question 15

Talk about the “Face” of the total station

Answer 15

Question 16

How do you setup a total station?

Answer 16

Question 17

What targets can angles be measured to?

Answer 17

• They can be measured to any target!!!!!!!!!
• However targets can take several forms:
• Nails in top of wooden pegs
• Metal bars cast in concrete
• Adhesive targets on objects
• PRISMS!

Question 18

What are the features of a prism assembly?

Answer 18

Question 19

What are the most important features on a prism and what do they do?

Answer 19

• Optical plummet: For centring prism over station with foot screws
• Pond bubble: For roughly centring the prism
• Plate level: For fine levelling the instrument

Question 20

What are the sources of error when measuring angles?

Answer 20

• Field or site errors:
• Instrument not level
• Miscentring
• Not removing parallax
• Incorrect pointing
• Poor weather and ground conditions
• Booking errors
• Errors in equipment:
• Equipment gets worn
• Axes of total station should be in proper adjustment
• Compensator error (causes tilt of horizontal and vertical axes)
• Horizontal collimation error (occurs when line of sight is not perpendicular to the vertical axis)
• THESE MUST BE CORRECTED ELECTRONICALLY
• Laser plummet error (occurs when the plummet does not look down the vertical axis)
• Circular bubble out of adjustment
• THESE MUST BE MANUALLY CORRECTED BY A QUALIFIED TECHNICIAN

Question 21

What is miscentring how will this affect your results?

Answer 21

• Occurs if total station and its targets are not exactly centred over their stations
• This results in incorrect horizontal angles measured
• These errors have the greatest affect over short distances

Question 22

How do you calculate Max angular error due to miscentring the total station?

Answer 22

• α = (e/D_AB).sin (θ/2) rads * 206265
• β = (e/D_BC).sin (θ/2) rads * 206265
• TO CONVERT RADS TO SECS YOU MUST MULTIPLY BY 206265

Question 23

How do you calculate miscentring error (i.e maximum angular error) due to miscentring targets?

Answer 23

• d = (m/D_AB) rads * 206265
• ∈ = (m/D_BC) rads * 206265

Question 24

How can we eliminate errors?

Answer 24

• Take a face left and face right reading
• This does not however solve errors due to electronic level or laser plummet
• Taking at least 2 rounds of reading enables errors to be detected