Methods of the amendment of the former charts compiled from the astronomical data.
|dc.description.abstract||With the completion of triangulation nets in Japan by the Land Survey Department in 1922, geodetic latitude and longitude were decided to be adopted for the compilation of chart instead of astronomical coordinates. Immediately after this decision, most of the astronomical survey data were damaged by fire of the great earthquake in 1923. Therefore, the actual reductions from astronomical to geodetic coordinates were carried out on the assumption that the triangulation points of the Hydrographic Office were coincident with those of the Land Survey Department, causing inevitably the following errors of some amount: (1) Error of astronomical observation spots amounts to 20”－30”（ 1s-2s, 0.5 km -1 km) in some cases. (Observational errors, deviation of plumb line) (2) Since the triangulation data were adjusted to astronomical base line, overestimating the accuracies of astronomical observations, the resulting charts may contain some distortion in figure. (3) After the World War II, on some assumption, Kobayasi reamended the charts which had been prepared from the astronomical data. But these reamended charts may still have error of some 100 m. Methods of reamendment to these charts are: (i) The errors due to the error of astronomical base line: The corrections to longitude and latitude shall be obtained by the method of least squares so as to minimize the differences between values of longitude and latitude of control points on charts and those of the same points on the topographical maps of the Land Survey Department (present Geographical Survey Institute), on each chart. Then the meridians and parallels shall be shifted for these corrections without changing the figure, and magnification shall be corrected by photograph. (ii) The distortion of figure: , The distortion can only be rectified by optical method using the topographical map and aerophotograph, at a temporary measure.||en_US|
|dc.title||Methods of the amendment of the former charts compiled from the astronomical data.||en_US|
|dc.bibliographicCitation.title||Report of Hydrographic and Oceanographic Researches||en_US|