A treatise on levelling, topography, and higher surveying (1876)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, b. 1840, ed · New York, D. Appleton and company · leaf 148
of theobjects. With these data the oblique angle can be reduced toits horizontal projection, either by descriptive geometry ormore precisely by calculation, thus : Let AH B be the observed angle, and A! H B the requiredhorizontal angle. Conceive a vertical IIZ, and a spherical surface, of whichH,… … thus forming a spherical triangle, A Z B, in which AB == hmeasures the observed angle ; Z A = Z measures the zenithdistance of the point A; and Z B = Z measures the zenithdistance of the point B. These zenith distances are observed directly, or given bythe observed angles of elevation or…
Surveying
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