Spatial

Question 1

How do you ensure tin is an accurate representation of the surveyed site?

Answer 1

• Additional shots not used in creating the tin
• Look at contours
• Look at tin in 3d viewer
• Take tin back to site and stake out the tin to check accuracy

Question 2

GPS calibration

Answer 2

Not sure?

Question 3

TS calbration

Answer 3

• Distance = over a baseline
• Check and adjust (measuring 2 faces to a target to see difference in observed bearings for tilt in each of the 3 axis)

Question 4

Level calibration

Answer 4

• 2 peg test
• set up in middle, observe 2 points
• shift so that you are close to one of the points and observe both points
• difference in height should be the same for both setups

Question 5

GPS errors

Answer 5

1. Satellite (positional error, geometry)
2. Signal (atmospheric, troposphere, ionosphere)
3. Receiver errors/receiver environment (plumbing, centring, height errors, multipath)

Question 6

Total station error sources

Answer 6

• Plumbing
• Instrument and target heights
• Prism constants
• Automatic target pointing (example of trimble 360 prism with LED lights)
• curvature and refraction

Question 7

Process for topographic surveys & checks undertaken

Answer 7

• Check plumbing (pole - before going into field, instrument and tripod targets - rotating plummets)
• Check instrument and target height (measure twice, different reference points)
• Measure backsight (check residuals)
• Check shot onto another known point (check residuals)
• Check shot before and after changing pole height
• Check backsight every 30min?
• Check shot onto known point after surveying
• Check backsight
• Check optical plummets before shifting to next station

Question 8

What control did you use?

Answer 8

Primarily old cadastral marks as the surey was undertaken in conjunction with an LT survey. Placed new marks where necessary to ensure a sufficient spread of site benchmarks for future work on the site.

Question 9

What accuracy was achieved and how did you know/quanitfy this?

Answer 9

• Point derivation reports on control marks
• Horizontal and vertical quality control targets in the controller and processing software

Question 10

Rule of thumb for contour intervals?

Answer 10

At least twice the expected accuacy of the tin.

Question 11

What extra information should be shown on the plans?

Answer 11

North point, scale bar, accuracy disclaimer, what has/hasn’t been surveyed disclaimer, coordinate system information, datum information (including date), easements