Practical Surveying for Surveyors' Assistants, Vocational, and High Schools (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 Excerpt: ...be necessary. The base line is taken inside the field when it is possible, as the lengths of the sights is thereby reduced to a minimum; but it is not essential that it be so taken, and it may be all outside of the field or partly inside and partly outside. The only imperative condition--using one base line--is that all corners must be visible from each end of the base line." "In locating the base line care must be taken to avoid small angles, as the sines of small angles change rapidly. (Angles under 150 and over 1650 must be obtained to the nearest 10 sees., which can be done by trebling the angle on the limb of the transit.) In the case of a rectangular field the best location for the base line is parallel to the short axis. This arrangement should be followed as closely as the topography will permit. The more irregular the field, the harder it is to avoid small angles, and more time and thought are required in the selection of the base line than in the case of the rectangular field. The length of the base line depends upon local conditions. In general, the longer it is, the more accurate the results; but it should never be less than one-third the length of the average sight. This is based on the assumption that the instrument used reads to 30 sees., and that each angle is doubled on the limb." Fig. 202 illustrates a field surveyed by the intersection method, AB being the base line, the only line measured. "The traverse method is applicable to any field regardless of the crops or topographical conditions. There is always a strip of land along the fence line that is not cultivated, and an open sight may be had along this strip, so the distance between corners may be chained without interfering with the growing crops. The radiation meth...