Question
Choose the CORRECT statements(s).
Statement Analysis
We need to evaluate each statement regarding the Earth's shape and reference systems.
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Statement 1: The spheroid is a mathematical surface of the Earth.
- Verdict: CORRECT
- Explanation: A spheroid (specifically an oblate spheroid) is a simplified, idealized geometric shape used to approximate the Earth's irregular shape. It's a mathematical model, not the Earth's true physical surface.
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Statement 2: Geoid is an equipotential reference surface of the Earth.
- Verdict: CORRECT
- Explanation: The geoid is defined as the surface of equal gravitational potential that best fits mean sea level. It represents the true shape of the Earth influenced by gravity and rotation, serving as a fundamental reference surface in geodesy.
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Statement 3: True shape of the Earth is perfect spheroid.
- Verdict: INCORRECT
- Explanation: The Earth's true shape is irregular and closely approximated by the geoid, not a perfect spheroid. While a spheroid is a useful model, it doesn't capture the true, complex shape.
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Statement 4: The WGS-84 datum varies from country to country.
- Verdict: INCORRECT
- Explanation: WGS-84 (World Geodetic System 1984) is a global geodetic datum and is consistent worldwide. While older or local datums might vary regionally, WGS-84 provides a standard reference system for the entire Earth.
Conclusion on Correct Statements
Based on the analysis, statements 1 and 2 accurately describe the spheroid and geoid concepts in geodesy.
Correct statements: 1, 2
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Important Questions from Levelling Methods
- Which one of the following is the purpose of taking a backsight observation in levelling?
- The observations of a reciprocal levelling operation carried out from two stations A and B are given in table. It is known that the instrument has collimation error. The correct staff reading over station B when the instrument is set very near to station A is ________ m (Rounded off to three decimal places).
Assume all other errors are negligible.Staff readings at station Instrument set very near to station A (m) B (m) A 1.275 2.005 B 1.040 1.660 - A level with the height of the instrument being 2.550 m has been placed at a station having a Reduced Level (RL) of 130.565 m. The instrument reads 3.665 m on a levelling staff held inverted at the bottom of a bridge deck. The RL of the bottom of the bridge deck is __________ m (rounded off to 3 decimal places).
- In levelling between two points P and Q on opposite banks of a river, the level was set up near P, and the staff reading on P and Q were 2.165 m and 3.810 m, respectively. The level was then moved and set up near Q and the respective staff readings on P and Q were 0.910 m and 2.355 m. The true difference of level between P and Q is __________ m (rounded off to 3 decimal places).
- Change Point (CP) in levelling refers to a location where
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