What is the full form of ‘REM’ ?

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Option B: Remote Elevation Measurement

Explanation & Concepts:
REM stands for Remote Elevation Measurement. It is a specialized function integrated into Total Stations that allows the operator to determine the height of an inaccessible point above a ground station without the need for a reflector (prism) to be placed at that exact target location.

Working Principle: The total station uses trigonometric principles to calculate the height. First, the observer sights a prism placed at the base of the object (or a point of known elevation) to determine the horizontal distance ($D$) and the reference vertical angle. The telescope is then tilted upward to the inaccessible point (e.g., top of a building), and the instrument records the new vertical angle ($\alpha$). The height $h$ is then calculated using the relationship $h = D 	imes 	an(\alpha)$.

Key Formulas: $h = D 	an(\alpha)$ — height calculation formula for REM; $\Delta H = H_i + D 	an(\alpha) - h_{prism}$ — elevation of point relative to instrument height

Key Points: REM is vital for surveying inaccessible features like transmission lines, bridges, or building heights.; It requires the user to know the horizontal distance to the point vertically below the inaccessible target.; Accuracy depends on the precision of the horizontal distance measurement and the vertical angle tracking.

Advantages: Eliminates the need for physical access to the target point.; Reduces time and labor costs in urban site measurements.; Highly efficient for measuring vertical structures.

Disadvantages: Accuracy decreases significantly with large horizontal distances.; Requires stable setup and accurate calibration of the vertical axis.; Sensitive to atmospheric refraction at large angles.

Applications: Measurement of bridge clearances.; Height estimation of high-rise building facades.; Verification of sag in overhead power lines.

Additional Info: Most modern Total Stations include a specific 'REM' mode in the software menu which automates the triangulation process.. Incorrect options were purely invented terminology; 'Elevation Measurement' is common in surveying, but 'Remote' correctly describes the non-contact nature of this feature.

Answer: B is correct — REM (Remote Elevation Measurement) allows for determining the elevation of points where placing a prism is physically impossible or impractical.

Exam Tip: Always ensure the horizontal distance ($D$) is accurately measured to the base point; an error in $D$ leads to an amplified error in $h$ as the vertical angle $\alpha$ increases.

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Option A: Rapid Elevation Measurement

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Option C: Raster Elevation Measurement

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Option D: Ranging Elevation Measurement

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