1. Types of Surveys ๐
| Survey Type | Purpose | Precision Required |
|---|---|---|
| Cadastral | Property boundaries, land titles | High (legal purposes) |
| Topographic | Elevation, terrain features | Medium-High |
| Construction | Setting out buildings, roads | Very High (mm level) |
| Hydrographic | Water body depths, shorelines | High (navigation safety) |
| Geodetic | Large area control networks | Highest (sub-mm) |
2. Leveling ๐
Determining elevation differences between points.
Basic Leveling Equation
Elevation B = Elevation A + BS - FS
HI = Elevation A + BS
BS (Backsight)
Reading on known elevation point. Always ADDED to elevation.
FS (Foresight)
Reading on unknown point. Always SUBTRACTED from HI.
HI (Height of Instrument)
Elevation of line of sight = Known Elev + BS
Leveling Errors
- Curvature: c = 0.0785Dยฒ (meters, D in km)
- Refraction: r = 0.011Dยฒ (meters, D in km)
- Combined (c-r): 0.0675Dยฒ โ 0.07Dยฒ
- At 1 km: c-r โ 0.07m = 7cm error!
3. Traverse Surveying ๐
Angular Closure
Interior angles sum = (n-2) ร 180ยฐ
Exterior angles sum = (n+2) ร 180ยฐ
Error distribution: Equally distribute angular error to all angles
Linear Closure
Departure = Distance ร sin(Bearing)
Latitude = Distance ร cos(Bearing)
ฮฃDep = 0 and ฮฃLat = 0 for closed traverse
Precision = Linear error / Total distance (e.g., 1:5000)
Adjustment Methods
- Compass Rule: Correction โ Distance (for equal angular & linear precision)
- Transit Rule: Correction โ Lat/Dep (for higher angular precision)
- Least Squares: Most rigorous, minimizes sum of squares
4. Area Computation ๐
Double Meridian Distance (DMD)
Area = ยฝ ฮฃ(DMD ร Lat)
- First DMD = First Departure
- Next DMD = Prev DMD + Prev Dep + Curr Dep
- Last DMD = Last Departure (check!)
Coordinate Method
2A = ฮฃ(Xn(Yn+1 - Yn-1))
Or: 2A = ฮฃ(Yn(Xn-1 - Xn+1))
Faster for coordinate-based surveys
5. Surveying Instruments ๐ญ
Total Station
Electronic theodolite + EDM combined. Measures angles and distances simultaneously.
Accuracy: 1-5mm + 1-3ppm for distance; 1" for angles
GNSS Receiver
Satellite-based positioning. RTK mode: cm-level accuracy in real-time.
Static survey: mm accuracy with post-processing
Level
Automatic/digital level for height determination. Self-leveling compensator.
Precision levels: ยฑ0.3mm per km double-run
6. Practice Questions ๐
Common Board Exam Questions
Q1: In a 5-sided closed traverse, what should be the sum of interior angles?
A: (n-2) ร 180ยฐ = (5-2) ร 180ยฐ = 3 ร 180ยฐ = 540ยฐ
Q2: The BS reading is 2.543m and FS is 1.876m. If BM elevation is 100.000m, what is the elevation of the new point?
A: HI = 100.000 + 2.543 = 102.543m. New Elev = 102.543 - 1.876 = 100.667m
Q3: What is the combined curvature and refraction error at 2km?
A: c-r = 0.0675 ร Dยฒ = 0.0675 ร 4 = 0.27m
๐ฅ GE Challenge ๐ฅ
Master field surveying! Leveling, traversing, area computation, instruments - precise measurements in any terrain!
Measure twice, mark once - the surveyor's creed!