733 HYDROGRAPHIC MANUAL Page 674 



is used for each State, where practicable, although in the larger States two or more 

 systems were necessary. These have been computed on two different types of projection : 

 the Lambert conformal conic for those States of an east-west extent proportionately 

 great as compared to their north-south extent; and the transverse Mercator projection 

 for those States with a proportionately great north-south extent. The coordinates on 

 the State systems have been computed for all geographic positions adjusted since 1935 

 and these are published in the official publications of the triangulation of the country. 



Details of these systems, the methods of making the computations and the methods 

 of plotting various types of surveys thereon, are given in several publications. They 

 are given in brief in Serial No. 624, Computation of Traverse by Plane Coordinates, 

 and in fuller detail in Special Publication No. 193, Manual of Plane Coordinate Com- 

 putation; Special Publication No. 194, Manual of Traverse Computation on the 

 Lambert Grid; and Special Publication No. 195, Manual of Traverse Computation 

 on the Transverse Mercator Grid. 



For the coordination of surveys on the systems m type (c) with hydrographic 

 surveys of this Bureau, no information is needed except the knowledge that the survey 

 is on one of the oflB.cial State systems and which system. 



733. Hydrographic Sheets From Air Photographic Surveys 



Where the shoreline and hydrographic control originate with air photographic 

 surveys (see 239) the information for the boat and smooth sheets will be furnished by 

 the Washington Office in the form of reversed tracing-paper prints, ozalid prints, 

 printed sheets, or map projector transfers. The form used will depend upon the con- 

 ditions peculiar to the project and will be stated in the project instructions. 



The short descriptions of stations, for the information of the hydrographer, will 

 be furnished on ozalid prints to be used by the hydrographic party when recovering 

 the stations and building the signals (see 2392). 



7331. Reversed Tracing Paper Prints 



Ordinarily the air photographic survey drawings are forwarded to the Washington 

 Office as soon as the location of the shoreline and the hydrographic control is completed. 

 These are reproduced in the Office to the same scale as the hydrographic surveys and 

 reversed copies are printed in black on tracing paper and furnished the hydrographic 

 parties. The ink used is slow drying and usually the print used in preparing a boat 

 sheet can also be used for preparing the smooth sheet some months later. 



The transfer of the shoreline and control is effected by superimposing the tracing 

 (inked side down) on the boat sheet or smooth sheet, so that corresponding projection 

 intersections are in coincidence, and burnishing down the details. Adjustments for 

 differences in the projections can be made by small shiftings of the tracing (see 7413). 



If the ink has dried before the smooth sheets are prepared, additional tracing-paper 

 prints will be furnished on request. 



7332. Ozalid Prints 



In some cases where the air photographic surveys are made at exactly the same 

 scale as the hydrographic survey and when sufficient time is not available to prepare 

 reversed tracing-paper prints, ozalid prints will be furnished the hydrographic party 

 for transfer of the shoreline and control. 



