PROBLEM 5. Points A and B are exactly 200 feet apart. With a level set up exactl

Question

PROBLEM 5. Points A and B are exactly 200 feet apart. With a level set up exactly midway between A and B, a surveyor obtained a rod reading at A of 6.22 ft. and a rod reading at B of 6.60 ft. The level was then moved to within a few inches of A. The surveyor then obtained a rod reading at A of 5.16 ft and a rod reading at B of 6.48 ft. Sketch both setups. Which point is higher? What is the true elevation difference between the two points? How much collimation error exists in the instrument for each 100 ft of shot? (Ignore earth curvature and refraction effects and assume that the very short shot is of O length.) (8 points)

Explanation / Answer

When the instrument is exactly at mid point dh1 = b1-a1 = 6.6- 5.22 = 1.38 ft this is the true difference in elevations of points A and B as the instrument is exactly at mid point. Clearly point A is higher than point B by 1.38 ft

When instrument a few inches from A dh2 = b2-a2 = 6.48- 5.16 = 1.32 ft

Now as the instrument is very close to point A thus the staff reading of point A would be practically negligibly affected by collimation. Thus when the instrument placed midway between points A and B that are 200 ft apart we have collimation error in reading at A of 0.06 ft and thus 0.06 ft is the collimation error per 100 ft or shot

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