Page 77 control and signal building 224 



224. Connection With Triangulation of Other Organizations 



Independent schemes of triangulation, which have been estabhshed in the project 

 area by other organizations, shall be connected to the triangulation of this Bureau 

 by strong figures in such a way that their positions may be computed and adjusted on 

 the North American datum of 1927, provided this is feasible. This provides additional 

 control for the contemporary surveys and for any future surveys in this particular area 

 by any agency. Such connections are especially desirable to the control stations of the 

 United States Corp^ of Engineers, which are located in harbors and along inland navi- 

 gable waterways, and the positions of their stations are valuable to the Bureau both for 

 the control of surveys and for cartographic purposes. 



Where a connection is to be made to triangulation of other agencies, a line connection 

 is preferable to a point connection, because a comparison of the length and azimuth will 

 give valuable data to be used in adjusting the scheme (see last paragraph on page 15, 

 Special Publication No. 120, Manual of Fhst-Order Triangulation). If neither method 

 is feasible, a connection by topographic methods should be made (see 236) . 



Representatives of other survey agencies should be contacted personally or by 

 correspondence to ascertain what control exists within the project area, and to obtain 

 positions and descriptions of stations and copies of the schemes. The latter will show 

 the disposition of the stations and the area covered by the survey. To tie in the scheme 

 properly, a connection should be made at three places strategically selected so that 

 an adjustment of the triangulation of the other agency can be made to fit the triangula- 

 tion of this Bureau. 



If practicable, the positions of stations established by other organizations should be 

 determined in lieu of establishing new stations nearby, provided the station marks are 

 in good condition and the station sites are in suitable locations. In such instances, two 

 standard Coast and Geodetic Survey reference marks shall be established at each station. 

 The disks shall be stamped with the name given to the station by the establishing 

 .organization, followed by the initials of that agency and the year the reference marks 

 are set, and numbered 1 and 2, provided no other Coast and Geodetic Survey reference 

 marks have been previously established at the station. 



Under no circumstances shall survey station marks of other 'organizations be 

 altered or amended by stamping. Neither shall they be moved, replaced, or reset unless 

 the project instructions so specify. • However, they should be reinforced with concrete 

 or by other methods that will tend to prolong their existence, especially if the mark is a 

 little loose or in danger of being dislodged from its original position. Special precautions 

 must be taken not to disturb or move the station mark in any way. 



225. Recovery of Stations 



Where new triangulation is connected to previously established triangulation, it is 

 necessary to verify the identification and recovery of the old stations, and to check 

 distances and directions to reference marks to ensure that the station marks have not 

 been moved. The two stations at the ends of the old line must be occupied and obser- 

 vations made to a third station of the original scheme. If the measured angles check the 

 original observations, the recovery of the old stations is assured. 



To assist in keeping current the records of descriptions of triangulation stations, 

 as well as to provide control for hydrographic surveys, the sites of all previously estab- 

 lished control stations within the area of the survey should be visited, if practicable, 

 and a thorough search made for each station and its reference marks. A report shall 



