surveying iii (topographic and geodetic surveys) - Modern Prepper

Figure 2-3. Methods Used to Compute Line EFThe illustrations in Figure 2-3 are quadrilaterals. This is the simplest and most economical figure usedto give a double determination or check on the length of the line, as computed through the quadrilateral.This figure will be used as the go forward line or base for the succeeding figure. In first-ordertriangulation, the figures must be such that they afford a double check and all stations are occupied.Single triangles should not be used in first-order triangulation and only rarely in second-ordertriangulation.2-36. Acceptable Error of Angle Measurements. Together with the criterion of length agreementbetween bases, and almost equal in importance, are the requirements limiting the acceptable error ofangle measurements. The limits imposed on angular errors serve to maintain a uniform accuracy alongthe chain of triangles. The specifications for procuring the required accuracy make use of other criteria,such as the number and strength of the geometrical figures between adjacent bases, the observation ofastronomical azimuths at specified intervals, and the accuracy of baseline measurements. All of theserequirements are subsidiary to the controlling tests of the agreement between the measured and thecomputed length of a base and the limits specified for angle errors, and they are essential in securingsustained accuracy and control.2-37. Standards of Accuracy. In review, the following standards of accuracy are rigidly applied tofield observations in order to obtain consistent results in procuring the required precision. Therequirements will vary, depending on the classification of the triangulation, be it first order or secondorder. Baseline-measurement accuracy. The strength of a single figure in a network. The sum of the strengths of figures (R1) between baselines. The maximum single-triangle closure. The average triangle closure between bases.2-21 EN0593