PLANE TABLE. 



25 



from the base line. From A and B the points G, D, E, 

 and F are intersected, and one sight is taken on G, 

 which is obviously too nearly in line with the base line 

 to be accurately intersected. Subsequently the table 

 is set up at C and oriented by taking sights on A, B, 

 D } E, and F. It is then easy to intersect G, and also get 



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FIG. 6. Plane-table method in which the table is set up at two stations and the 

 remaining three are located by intersections. 



a sight on H, which was not visible before. 77 may be 

 intersected from G. (See fig. 7.) 



A fourth method is employed when the table must 

 be set up at an unknown point from which three or 

 more known points are visible. This is the " three- 

 point problem," in which the suveyor "picks up" his 



