Surveying and tables by Wentworth G. A. (George Albert) 1835-1906

Author:Wentworth, G. A. (George Albert), 1835-1906
Language: eng
Format: epub
Tags: Surveying
Publisher: Boston, Ginn
Published: 1903-03-25T05:00:00+00:00

^-'"D

Fig. 40

Let AB (Fig. 40) represent an inaccessible line whose extremities A and B only are known, and B invisible from A.

Set flagstaffs at convenient points, C and D. Find the bearings and lengths of AC, CD, and DB, and then proceed to find the latitude and departure oiAB.

Example.

lowing notes (see Eig. 40):

Suppose that we have the fol-

LAND SURVEYING

63

The northing of AB is AE = 2.06, and the easting, EB = 8.04. These numbers may be entered in the tablet in the columns N. and E., opposite the side AB.

If the bearing and length of AB are required,

tan BAE =

BE 8.04

AE

Hence, the angle BAE = 75° J Also,

2.06

= 3.903.

AB = ^AE* + TH? = V8.04 2 + 2.06 2 = 8.30. Therefore, the bearing and length of AB are N. 76° 38' E. and 8.30.

To make a Plot. A plot or map may be drawn to any desired scale. If a line 1 inch in length in the plot represents a line 1 chain in length, the plot is said to be drawn to a scale of 1 chain to an inch. In this case (Fig. 41) the plot is drawn to a scale of 8 chains to an inch.

Draw the line NAS to represent the meridian, and lay off the first northing 4.B'=8.14. Through B draw an indefinite line perpendicular to NS and lay off B'B, the first easting, = 2.96. Draw AB ; then the line AB represents the first side of the field. Through B draw BC n perpendicular to BB\ and make BC" = 1.71, the first southing. Through C" draw C"C perpendicular to BC", and equal to 4.70, the second easting. Draw BC. The line BC represents the second side of the field. Proceed in like manner until the field is completely represented. The extremity of the last line F*A, measured from F\ should fall at A. test of the accuracy of the plot

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