convenientshore baseto triangulate offshore distances from aline. No matter how you get offshoredistances, however, offshore points cannot be markedlike ground points with hubs or stakes. Therefore, inthe location of offshore points, there must usually becoordination between a survey party on the beach anda party afloat.OFFSHORE LOCATION BY CHAININGFigure 10-28 shows a situation in which offshorelocations of piles for a wharf were determined bychaining. We will call each series of consecutive pilesrunning offshore a line and each series runningparallel to the shore a row. Alignment for each linewas obtained by transit—set up on a shore base lineoffset from the inboard row of piles. In each line thedistance from one pile to the next was chained, asshown.In figure 10-28 the lines are perpendicular to thebase line, which means that the angle turned from thebase line was 90° and the distance from one transitsetup to the next was the same as the prescribeddistance between lines. If the lines were notperpendicular to the base line, both the angle turnedfrom the base line, the distance from one transit setupto the next, and the distance from the base line to thefirst offshore pile in each line would have to bedetermined.Consider figure 10-29, for example. Here theangle between each line and the base line (either asprescribed or as measured by protractor on a plan) is60°40´. You can determine the distance betweentransit setups by solving the triangle JAB for AB, JAbeing drawn from transit setup B perpendicular to theFigure 10-29.—Offshore location in line oblique to the baseline.Figure 10-28.—Offshore location by chaining10-27
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