Which method is commonly used to reduce the effect of collimation error when levelling across an obstacle?
Correct answer: D. Taking equal sight lengths on both sides
- A. Increasing the difference between sight lengths
- B. Using a shorter staff at each point
- C. Taking several foresights at one point
- D. Taking equal sight lengths on both sides
Explanation
Equal backsight and foresight distances make the collimation error equal in both readings, so it cancels in the difference. Unequal sight lengths allow the error to affect the computed difference in elevation.
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Surveying covers measurement of distances, angles and elevations, traversing, levelling, contouring, plane table work, theodolites, total stations and basic photogrammetry. It includes error adjustment, coordinate calculations, area and volume determination, and the distinction between accuracy and precision, as well as between temporary and permanent adjustments.
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