chapter 1.2

PART A: SHORT-ANSWER EXAM QUESTIONS WITH ANSWERS

These are classic scoring questions. Memorize the keywords and you’re safe.

1. Define geodesy.

Answer:
Geodesy is the science of measuring and representing the Earth’s shape, size, gravity field, and temporal variations, and establishing accurate coordinate systems.

2. What did Eratosthenes contribute to geodesy?

Answer:
He measured the Earth’s circumference using shadow angles and distance, proving the Earth is spherical with remarkable accuracy.

3. Differentiate between ellipsoid and geoid.

Answer:

  • Ellipsoid: Mathematical, smooth surface used for calculations

  • Geoid: Irregular gravity-based surface approximating mean sea level

4. What is a datum?

Answer:
A datum is a reference framework defining the origin, orientation, and scale for coordinate systems.

5. Why is Everest 1830 unsuitable for GNSS?

Answer:
It is:

  • Local and outdated

  • Not Earth-centered

  • Causes distortions when used with satellite-based systems

6. What is ITRF?

Answer:
International Terrestrial Reference Frame is a global, Earth-centered, time-dependent reference frame used for precise positioning.

7. Why is geodesy important in Nepal?

Answer:
Because Nepal lies in an active tectonic zone, requiring continuous monitoring of crustal movement, infrastructure deformation, and hazards.

8. What is scale factor in map projection?

Answer:
The ratio of distance on the map grid to the corresponding distance on the Earth’s surface.

9. Define RTK surveying.

Answer:
Real-Time Kinematic surveying is a GNSS technique providing centimeter-level accuracy using real-time correction data from a base station or CORS.

10. Mention two engineering applications of geodesy.

Answer:

  • Tunnel alignment

  • Dam deformation monitoring

PART B: NUMERICAL PROBLEMS (EXAM + FIELD STYLE)

Now the math. This is where people panic for no reason.

Problem 1: GNSS Height Conversion

Given:

  • Ellipsoidal height (h) = 520.000 m

  • Geoid undulation (N) = 43.200 m

Find orthometric height (H).

Formula:

𝐻=β„Ž−𝑁

Solution:

𝐻=520.000−43.200=476.800 π‘š

Answer:
Orthometric height = 476.800 m

Problem 2: Scale Factor Correction

Given:

  • Ground distance = 1,200 m

  • Scale factor = 0.9996

Find grid distance.

Formula:

π·π‘”π‘Ÿπ‘–π‘‘=π·π‘”π‘Ÿπ‘œπ‘’π‘›π‘‘×scale factor

Solution:

π·π‘”π‘Ÿπ‘–π‘‘=1200×0.9996=1199.52 π‘š

Answer:
Grid distance = 1199.52 m

Problem 3: Datum Shift Conceptual (Short Numerical)

Given:
Coordinate shift from Everest 1830 to WGS 84:

  • Ξ”X = +120 m

  • Ξ”Y = −85 m

Original coordinate:

  • X = 500,000 m

  • Y = 3,100,000 m

Find new coordinate.

Solution:

  • X = 500,000 + 120 = 500,120 m

  • Y = 3,100,000 − 85 = 3,099,915 m

Problem 4: GNSS Baseline Accuracy

Given:
Baseline length = 10 km
Accuracy = ±(5 mm + 1 ppm)

Calculation:
1 ppm of 10 km = 10 mm

Total error:

5+10=15 mm

Answer:
Baseline accuracy = ±15 mm

PART C: RTK WORKFLOW (REAL FIELD VERSION, NO FAIRYTALES)

This is how it actually goes down on-site.

Step 1: Reconnaissance

  • Check sky visibility

  • Avoid trees, buildings, power lines

  • Verify mobile network (if using NTRIP)

If signal drops, accuracy drops. Physics does not negotiate.

Step 2: Base Station Setup (If No CORS)

  • Set tripod on known control point

  • Measure antenna height carefully (twice, minimum)

  • Input correct coordinate system and datum

  • Start broadcasting corrections

One wrong antenna height = garbage survey.

Step 3: Rover Initialization

  • Power on rover

  • Connect to base or NTRIP

  • Wait for FIXED solution

  • Do not rush this part like it owes you money

Step 4: Coordinate Verification

  • Occupy a known point

  • Check error (should be within tolerance)

  • If error is large, stop and fix it

Blind trust is how maps become lies.

Step 5: Data Collection

  • Collect points with FIXED solution only

  • Average points if required

  • Maintain consistent antenna height

FLOAT solution is not your friend.

Step 6: Quality Control

  • Re-occupy points

  • Check closure

  • Export data with correct CRS

If you skip QC, the exam marker and the Earth both judge you.

Step 7: Post-Processing (Optional but Smart)

  • Compare RTK with static control

  • Adjust if necessary

  • Document everything

Surveying without documentation is just vibes.

FULL MOCK EXAM PAPER

Geodesy & Surveying

Time: 3 Hours
Full Marks: 60
(Attempt questions as instructed. Figures to the right indicate full marks.)

SECTION A: VERY SHORT ANSWERS

(10 × 2 = 20 marks)
Attempt ALL questions.

  1. Define geodesy.

  2. State two assumptions made by Eratosthenes in his experiment.

  3. What is meant by an Earth-centered datum?

  4. Write the relationship between ellipsoidal height, geoid undulation, and orthometric height.

  5. What is the main disadvantage of Everest 1830 datum?

  6. Define geoid.

  7. What does “FIXED solution” mean in RTK?

  8. Mention two sources of GNSS error.

  9. What is scale factor in map projection?

  10. Write any two applications of geodesy in Nepal.

SECTION B: SHORT ANSWER QUESTIONS

(Attempt ANY 4) (4 × 5 = 20 marks)

  1. Explain the evolution of geodesy from classical to satellite geodesy.

  2. Differentiate between ellipsoid and geoid with neat sketches.

  3. Explain the importance of geodesy in engineering construction projects.

  4. Describe the national geodetic framework used in Nepal.

  5. Explain the principle of RTK GNSS surveying.

  6. What problems arise when using local datums with GNSS observations?

SECTION C: LONG ANSWER / NUMERICAL

(Attempt ANY 2) (2 × 10 = 20 marks)

a) Explain the concept of Digital Earth.
b) Discuss its applications in disaster management in Nepal.

OR

a) Explain horizontal and vertical datums with reference to Nepal.
b) Why is geoid modeling important in mountainous regions?

OR

a) Describe the complete RTK surveying workflow.
b) Explain quality control measures in GNSS surveying.

NEPAL SURVEY DEPARTMENT–STYLE PRACTICAL QUESTIONS

These are field + calculation questions. No mercy, but predictable.

PRACTICAL 1: GNSS HEIGHT CONVERSION (6 marks)

Given:
Ellipsoidal height (h) = 612.450 m
Geoid undulation (N) = 46.230 m

Required:
Calculate the orthometric height.

Formula:
H = h − N

Answer:
H = 612.450 − 46.230 = 566.220 m

(Marks are lost if units are missing. Yes, really.)

PRACTICAL 2: SCALE FACTOR CORRECTION (6 marks)

Measured ground distance = 2,500 m
Projection scale factor = 0.9996

Calculate grid distance.

Grid distance = 2,500 × 0.9996
= 2,499.00 m

PRACTICAL 3: RTK FIELD PROCEDURE (8 marks)

Question:
Describe the procedure for conducting an RTK survey when no CORS station is available.

Expected points (any 4):

  • Selection of stable control point

  • Base station setup with known coordinates

  • Accurate antenna height measurement

  • Rover initialization and FIXED solution check

  • Occupation of check points

  • Data validation and documentation

Miss three of these and the examiner mentally sighs.

PRACTICAL 4: DATUM TRANSFORMATION (10 marks)

Given:
Coordinate shift from Everest 1830 to WGS 84:
Ξ”E = +135 m
Ξ”N = −92 m

Original coordinates:
E = 320,450 m
N = 3,112,800 m

Find transformed coordinates.

E = 320,450 + 135 = 320,585 m
N = 3,112,800 − 92 = 3,112,708 m

PRACTICAL 5: GNSS BASELINE ACCURACY (10 marks)

Baseline length = 15 km
Accuracy = ±(5 mm + 1 ppm)

1 ppm of 15 km = 15 mm
Total error = 5 + 15 = ±20 mm

EXAMINER FAVORITE ONE-LINE ANSWERS

Memorize these. They print marks.

  • “Nepal lies in an active tectonic zone, making geodetic monitoring essential.”

  • “GNSS requires Earth-centered reference frames for accuracy.”

  • “RTK accuracy depends on satellite geometry, datum, and field procedures.”

FINAL REALITY CH

ECK

If you can:

  • Finish this paper in under 2.5 hours

  • Keep formulas straight

  • Not panic at RTK questions

You’re not just passing. You’re annoying the topper.

If you want next, we can go even deeper:

  • Viva-style oral questions

  • Common mistakes Nepal examiners punish

  • Field sketch questions with marking scheme

Geodesy doesn’t care about confidence. Only math and discipline survive.


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