surveying iii (topographic and geodetic surveys) - Modern Prepper

PART B - MEASURING ANGLES3-11. Triangulation. Triangulation affords a rapid and accurate method of surveying a large area byeliminating the necessity of measuring the length of every line. In any triangle, if we know the values ofall three angles and the length of one side of the triangle, we can calculate the length of the other twosides. Having calculated the length of the unknown sides, we can use them as sides of known length foradjacent triangles. With this simple procedure, we could continue and calculate lengths throughout theentire series of connected triangles. However, we need not measure all three angles. The properties of atriangle are such that if we can measure any two angles, we can compute the value of the third.a. This procedure does not guarantee that the calculated value of the unknown angle will be its truevalue. Any error in the original measurement will be reflected in the calculated angle; therefore, therewould be no tangible reference for adjusting the triangulation on completion of the survey. Certaininstruments and field techniques are employed which greatly reduce the possibility of error. Many ofthese techniques will be brought to your attention during the remainder of this lesson. Certainmathematical computations are applied to the data so that any error is distributed throughout the entiresystem. This is the primary task of the data computer. The persistent elimination of conditions likely tocause errors makes their occurrences rare and allows for isolation and immediate remedy.b. Accuracy should be maintained throughout the triangulation. Use care when operatinginstruments, and pay strict attention to the methods. Observing the proper methods ensures thatsystematic and accidental errors are kept within the prescribed limits and that no part of the systemexhibits undue weakness.3-12. Theodolites. A theodolite is a precision surveying instrument used for the accurate measurementof angles. It consists of an alidade with a telescope. It is mounted on a base carrying an accuratelygraduated horizontal circle and equipped with necessary levels and reading devices. The alidade usuallycarries a graduated vertical circle. There are two general types of theodolites, repeating and direction. Arepeating theodolite is designed so that successive measures of an angle may be accumulated on agraduated circle. The reading of the accumulated sum is divided by the number of repetitions to obtainthe observed angle. On a direction theodolite, the circle remains fixed while the telescope is pointed ona number of signals in succession. The circle is read for each direction. The direction theodolite is thepreferred instrument used in higher-order triangulation. The quality of a theodolite is not measured byits size or the minutes on the least reading of the micrometers, but by the beat measure of excellence inits performance in actual fieldwork.3-13. Wild T-3 Precision Theodolite. Refer to Figure 3-4, page 3-16. The wild T-3 precisiontheodolite is a 0.2-second, prism microscope type of direction theodolite and is a satisfactory first-orderinstrument. The principal operating characteristic of this type of instrument is the method of reading thecircles by means of an auxiliary telescope (microscope) alongside the sighting telescope. Both sides ofthe circle are reflected simultaneously in this reading microscope through a chain of prisms. A3-15 EN0593