STADIA AND PLANE-TABLE SURVEYING 109 



along the line ab, move the table horizontally until the tele- 

 scope is accurately directed to B. The table is then clamped 

 and another point, as c, may be platted by directing the tele- 

 scope to C and at the same time having the edge of the alidade 

 ruler in contact with the point a; the line ax is then drawn and 

 the distance AC, measured by stadia or otherwise, is laid off 

 to scale, giving the point c. 



Plotting by Intersection. After the line ax in the preceding 

 example has been drawn, the point c can be located without 

 measuring the distance ac. This is done by moving the table 



f>Jne Tab/a at C 

 FIG. 3 



to B, platting the line by in a manner similar to line ax, and 

 then bringing these two lines to intersection. 



Platting by Resection. When the plane table is set up on 

 a point C, Fig. 3, not platted on the board, and the points A 

 and B have already been platted, measure the distances CA 

 and CB. Then, with these distances, to the scale of the map, 

 as radii, swing arcs from a and b as centers. The point 

 of intersection of these arcs is the platted position of the 

 point C, and the table can then be oriented in the usual manner. 



The Three-Point Problem. Let the plane table be set over 



