9441 



HYDROGRAPHIC MANUAL 



Page 864 



9441. Computation and Adjustment by Using Geographic Positions 



The positions iii a buoy traverse may be computed by geographic positions either 

 on Form 27, Position Computation, Third-Order Triangulation, or on Form 596, 

 Position Computation Traverse. Form 27 is preferable because two positions can 

 be computed on each copy of the form. 



To check traverse computations, the positions shoukl be computed independently 

 by two different persons on separate copies of the form. If the results agree, one set 

 of the computations may be destroyed. 



The adjustment of a traverse computed by geographic positions is shown in table 

 30. The fixed position of the initial buoy is entered in the "Adjusted position" column. 

 The traverse computations are started from this position. In the column "Position 

 from traverse computations," are listed the computed geographic positions of all the 

 buoy stations in the traverse, including that of the terminal buoy, whose fixed position, 

 in addition, is entered in the "Adjusted position" column. The differences in latitude 

 and longitude between the computed and the fixed positions of the terminal buoy are 

 entered on the last horizontal line in the column headed "Adjustment for closure 

 error." This is the closure error of the traverse. This error is proportioned accord- 

 ing to distance from the initial buoy and the proper proportional part is applied to each 

 buoy in the traverse. The proportion is based on the progressive distances entered 

 in the column headed "Sum distance." 



Geographic positions of buoy stations should alw^ays be expressed in degrees, 

 minutes, and meters. This eliminates the many conversions of seconds to meters, and 

 vice versa, and the chance of making errors in such conversions. 



9442. Computation by Rectangular Coordinates 



The positions of stations in a line of traverse buoys may be computed by rectan- 

 gidar coordinates in a manner similar to the computation of land traverses which is 

 explained in any good textbook on elementary surveying. This is the familiar com- 

 putation by latitude and departure, modified to give correct geographic positions. 



