72 



ANGULAR SURVEYING 



SOLUTION. The area S' of GDH is equal to 5 3.58 = 1 .42 A., 

 or 14.2 sq. ch. Substituting in the formula, 



8.93 sin 61 



PROBLEMS ON INACCESSIBLE LINES 

 Problem I. To determine the length of a line, AB, whose one 

 end A is accessible and the other end B, is visible but not accessible. 



Set the transit at A, 

 Fig. 3, and turn off 

 an angle BAC, which, 



Jl 



if practicable, should 

 be made equal to 90. 

 Measure along AC a 

 distance of about 300 

 or 400 ft., and measure 

 the angle C. Then, if 



FIG. 3 



4=90, AB = AC tan 

 C. For any other angle 



sin B 

 Problem II. To 



determine the angle between two lines A B and CD, whose point of 

 intersection P is inaccessible; also, the distances BP and DP. 



This problem is of frequent occurrence in railroad work, the 

 two given lines being the center lines of two tracks that are 

 to be connected by a curve. 



Measure the distance BD, Fig. 4, and the angles K and L. 



BD sin L 

 Then, M= 180- (K+L), I = K+L, BP=~ : , and 



DP = 



BD sin K 

 sin M 



sin M 



