2394 



HYDROGRAPHIC MANUAL 



Page 102 



ig) The sextometer method (see 2382), where the distance to be measured from the station located 

 by the radial plot does not exceed 250 meters. The distance and azimuth shall be shown on the boat 

 sheet as in method (6) . Stations so located shall be symbolized by blue circles on the boat and smooth 

 sheets as in (e). 



2394. Supplemental Stations 



Infrequently and in extraordinary circumstances, the liydrographer will require 

 supplemental stations which he is not prepared to locate by one of the methods listed 

 in 2393. These can sometimes be selected from, or located by reference to, the map 

 or photographic detail as described here. All stations so located shall be symbolized 

 by circles, 3 mm in diameter, in green ink on the boat and smooth sheets, 



A. SELECTED FROM MAP DETAIL 



If necessary, points on the planimetric map or boat sheet, which have not been 

 indicated by circles but w^hich are well-defined detail, such as small buildings, dock 

 comers, sharp rocky pomts, and forks of streams may be used as hydrographic signals. 

 Supplemental stations may be located by reference measurements to such detail, if 

 the objects themselves are not convenient for use as signals or as sites for the erection 

 of signals. Since some of the objects may have been located by proportional adjust- 

 ment rather than by intersection when the map was compiled, signal location from 

 such detail must be avoided whenever practicable. 



B. LOCATED FROM PHOTOGRAPHIC DETAIL 



If the photographs are available in the field and are of recent date, photographic 

 detail may be identified on the ground at, or near, which signals may be built. Such 



Figure 16.— Method of adjusted distances. 



FiouRE 17.— Paper-strip method. 



detail may include small detached rocks, ends and forks of small sloughs, intersections 

 of fences or ditches, small clumps of brush, sharp or distinctive points of land or 

 vegetation, and other ground detail which can be located on the photographs within 0.3 

 to 0.4 mm. 



