Engineering Surveying Week 2 Flashcards
What are the three types of angles?
- Horizontal
- Vertical
- Zenith
What is a horizonal angle?
- Angle in the horizontal plane between vertical planes
What is a vertical angle?
- 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
What is the zenith angle?
- Angle between vertical line above instrument and the line of sight
- Angle of elevation - 90° = Zenith Angle
What equipment do we have for measuring angles?
- Total stations
- Theodolite (ANGLES ONLY)
- Targets (e.g nails in top of wooden pegs, special devices mounted on tripods, metal bars set in concrete)
What can total stations do?
- Angle and distance measurements
- They measure horizontal and vertical angles and slope distances
- Large amounts of storage for data
How do you select the right total station to measure angles depending on your tolerance?
- 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
Learn this diagram on the principles of the total station
What are the three axis on a total station?
What are the two angle reading systems on a total station?
- Horizontal circle
- Vertical circle
How do you level the total station in the horizontal plane?
- Use electronic level in conjunction with its footscrews
How do you level the total station in the vertical plane?
- Done AUTOMATICALLY one the horizontal circle has been put into horizontal plane
What are the 16 components of a total station?
- Trivet (can be attached to a
tripod) - Tribrach clamp (to
detach/secure the total station
to the trivet) - Tribrach
carries the footscrews
The tribrach may be
detachable –useful when
traversing (dealt with later in
the module) - 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. - Vertical tangent screw - (to
move the telescope
up/down) - Collimator - (to roughly
sight/point to the target) - Carrying handle
- Objective lens
- Vertical circle
- Horizontal tangent screw
- Keyboard and LCD screen
- 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 - Circular bubble (pond bubble) 16
– used to roughly level the
instrument - Eyepiece (with cross-hairs on
a diaphragm)
Parallax must be eliminated - Image focus ring – to focus
the image - Standards
What does the microprocessor do on the total station?
- Performs multiple functions with main one calculating angles and distances
Talk about the “Face” of the total station
How do you setup a total station?
What targets can angles be measured to?
- 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!
What are the features of a prism assembly?
What are the most important features on a prism and what do they do?
- Optical plummet: For centring prism over station with foot screws
- Pond bubble: For roughly centring the prism
- Plate level: For fine levelling the instrument
What are the sources of error when measuring angles?
- 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
What is miscentring how will this affect your results?
- 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
How do you calculate Max angular error due to miscentring the total station?
- α = (e/DAB).sin (θ/2) rads * 206265
- β = (e/DBC).sin (θ/2) rads * 206265
- TO CONVERT RADS TO SECS YOU MUST MULTIPLY BY 206265
How do you calculate miscentring error (i.e maximum angular error) due to miscentring targets?
- d = (m/DAB) rads * 206265
- ∈ = (m/DBC) rads * 206265
How can we eliminate errors?
- 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
