206 



HYDROGRAPHIC MANUAL 



plotted with a beam compass and metric 

 scale. Dividers can be used for short dis- 

 tances, but they become less accurate when 

 they are spread appreciably. The dm. and dp. 

 distances in meters shall be marked by fine 

 prick points adjacent to each set of projec- 

 tion lines and connected by fine pencil lines 

 discussed in 6-16. As a check of the plot- 

 ting, and to compensate for any possible dis- 

 tortion, the back dms. and dps. must also be 

 plotted from the north parallel and west 

 meridian (Fig. 78). In the event there is 

 distortion, it shall be proportioned between 

 the parallel dm. and parallel dp. lines. The 

 position of the station at the intersection of 

 the final dm. and dp. lines is marked as 

 stated in 6-19. It is symbolized by a red 

 equilateral triangle, 4.5 mm. on a side with 

 base parallel to the lines of latitude and the 

 station name is inked in red (Fig. 79). The 

 symbol is readily formed in pencil by using 

 a thin plastic template having the cut-out 

 triangle and inked lines for orientation, or 

 by drawing the sides tangent to a 2.6 mm. 

 circle. Before inking, the triangulation point 

 shall be verified by the same method or by 

 use of special latitude and longitude scales. 



6-21 Topographic stations. — Reverse 

 blueline prints of photogrammetric compila- 

 tions are furnished on stable plastic material 

 for use in transferring topographic stations 

 and shoreline detail to the smooth sheet (see 

 4-10 to 15). Before transferring a station 

 point, a proportional adjustment must be 



I IT — I 



_L li_L_ 



P" 



rSM 



f- -Badtdp. - 



Tl/ 



■n 



Figure 78. — Control station plotted by dms. and dps. 

 on a distorted sheet. 



made to compensate for any difference be- 

 tween the projections. 



Stations located by planetable methods 

 shall be transferred to the smooth sheet by 

 pricking through a tracing of the topograph- 

 ic or graphic control sheet. The same care 

 is required to adjust differences in the pro- 

 jections. Stations may also be transferred 

 by use of dividers or a beam compass. 



Topographic stations are symbolized by 

 red circles 3.0 mm in diameter (Fig. 79), 

 and the station name is inked in red. Sta- 

 tions which have been marked by a standard 

 topographic disc shall be indicated on the 

 sheet by the letter "m" in parentheses, (m), 

 in black ink. 



6-22 Hydrographic stations. — Hydro- 

 graphic stations are those located by sextant 

 fixes or cuts (see 4-26). They shall be care- 

 fully replotted on the smooth sheet. If there 

 is distortion in the sheet, or if stations are 

 considerable distances away, the position 

 should be computed and the station plotted 

 by dms. and dps. The index of the sounding 

 volume should be carefully inspected to be 

 certain that all available data are used to 

 determine the correct position of the station. 

 Such stations are symbolized by blue circles 

 3.0 mm in diameter and the station names 

 lettered in blue (Fig. 79). 



Where the position of a hydrographic sta- 

 tion is subsequently determined by topo- 

 graphic or photogrammetric methods, the 

 station shall be plotted and symbolized as in 

 6-21. 



6-23 Supplemental stations. — Supple- 

 mental stations are sometimes established 

 during progress of hydrography by spotting 

 on the boat sheet a point which has been 

 identified on a topographic map or air 

 photograph. Unless such points are located 

 later by other methods, they shall be sym- 

 bolized by green circles 3.0 mm in diameter 

 and the station names inked in green (Fig. 

 79). 



6-24 Station names. — Station names on 

 the smooth sheet must always agree with 

 those on the boat sheet, the topographic 

 sheets or photogrammetric compilations, and 



