surveying iii (topographic and geodetic surveys) - Modern Prepper

length or side is known, and all three angles are measured. The other lengths or sides of the triangles arecomputed by applying the law of sines (sin) (Figure 2-1).Figure 2-1. Solving Angles and Using the Law of Sinesb. To begin work on a net of triangulation, the length of the starting line is required. The finalcomputation of the positions of the new stations, as well as the final azimuths, is done after thetriangulation is complete from one line of known length to another and after the net has been adjusted.The azimuth, latitude, and longitude are obtained from astronomic observations made during or after thetriangulation observations.2-34. Classification of Triangulation. The basis of classification of triangulation is the accuracy withwhich the length and azimuth of a line of the triangulation are determined. Higher order triangulation isperformed under two primary orders of accuracy. These orders are subdivided to give a total of fivedifferent degrees of precision. The principal criterion is that the discrepancy between the measuredlength of a baseline and its length, as computed through the triangulation net from the next precedingbase, shall not, after adjustment, be greater than the length closure shown for each class.a. First-Order Triangulation. There are three classes of first-order triangulation. Class I surveys are the most precise class of survey and must have a length closure of 1 partin 100,000. Its use is generally restricted to surveys for scientific purpose. These includeestablishing and testing missile and satellite systems, and performing studies of the shiftingof the earth's crust and the tilting of landmasses. Class I is also the basis for accurate landsurveys in highly developed areas. Class II must have a length closure of 1 part in 50,000. The basic national-control net shouldbe composed of arcs of triangulation of thisEN0593 2-18