. A treatise on surveying and navigation: uniting the theoretical, the practical, and the educational features of these subjects. nglesBA C, BAD, and at B we measureor observe the angles ABC, ABD,we then have sufficient data to deter-mine the points C and D, and the line CD. With equal facility that we determine the point C, we can deter-mine the point E, or F, or G, or any other visible point. Thus we may determine all the sides and angles of the figureCEFGHD, or any visible part of it, by triangulating from thebase AB. The lines forming the triangles are not drawn, except those to thepoints
. A treatise on surveying and navigation: uniting the theoretical, the practical, and the educational features of these subjects. nglesBA C, BAD, and at B we measureor observe the angles ABC, ABD,we then have sufficient data to deter-mine the points C and D, and the line CD. With equal facility that we determine the point C, we can deter-mine the point E, or F, or G, or any other visible point. Thus we may determine all the sides and angles of the figureCEFGHD, or any visible part of it, by triangulating from thebase AB. The lines forming the triangles are not drawn, except those to thepoints C and D ; we omitted to draw others to avoid confusion. After any line, as FG, has been computed, it is well to measure it,and if the measurement corresponds with computation, or nearly so,we may have full confidence of the accuracy of the work as far as ithas been carried. We may take CD as the base, and determine any visible numberof points, as A, B, H, F, G, &c, trace any figure and determine itsarea, or show the relative positions and distances of objects fromeach other, such as buildings, monuments, trees, < THE PLANE TABLE. 147 But to make the computation, triangle after triangle, for the sakeof making a map, would be very tedious, and to measure every sideand angle would be as tedious, and to facilitate this kind of operationwe may have an instrument called the PLANE TABLE. The plane table is exactly what the name indicates ; it is a planeboard table, about two feet long, and twenty inches wide, resting ona tripod, to which it is firmly screwed, yet capable of an easy motionon its center, having a ball and socket like a compass staff. Directly under the table is a brass plate, in which four milledscrews are worked, for the purpose of adjusting the table, thescrews pressing against the table. To level the table, a small detached spirit level may be level being placed on the table over two of the screws, thescrews are turned contrary ways, until the level
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Keywords: ., boo, bookcentury1800, booksubjectnavigation, booksubjectsurveying
