![]() A NEW EARTH MODEL INCLUSION (DATUM OR ELLIPSES) IN SPRINGA new Earth model can be included in SPRING through a carefully edition of the “datum” file, stored at <c:>\<spring installation folder>\<etc>. In order to do this it is required to have the datum parameters: (1) major semi-axis or equatorial radius, (2) flattening, (3) translation in X, (4) translation in Y, (5) translation in Z. These parameters are normally computed and published by the Geodesy and Cartographic official agencies of each country. In the “datum” structured file the first element is an integer number that identifies the existing projections in SPRING. These identifiers have to be kept and they can not, by no means, be changed. The identifiers actually valid are: (0) NOPROJECTION (does not edit this line), (1) UTM, (2) MERCATOR, (3) GAUSS, (4) LAMBERT MILLION, (5) LAMBERT, (6) POLYCONIC, (7) LATLONG, (8) POLAR STEREOGRAPHIC, (9) BIPOLAR OBLIQUE, (10) ALBERS, (11) MILLER. The second element in the “datum” structured file is the name used by SPRING in the projection interface for each datum. The next elements are the parameters described above, in the first paragraph of this document. It is important to notice that there are three situations where the three last parameters (the translations) can be null: (a)When the countries official datum is used as reference for any other datum. In Brazil, for instance, the current datum is the SAD-69 and it is the datum used as reference in SPRING. Its parameters are: 6378160, 3.352892e-03, 0, 0, 0. Any other datum has to have the translations separating its origin from the SAD-69 origin. (b)When the datum used as a reference is a global datum, geocentered, such as the WGS-84, the parameters have to be 6378137, 3.352811e-03, 0, 0, 0.. Any other datum have to have the translations separating its origin from the WGS-84 origin. (c)When just an ellipsoid is used as a reference. For the Hayford ellipsoid, also known as international ellipsoid from 1924, the parameters must be 6378388, 3.367003e-03, 0, 0, 0. Suppose that a SPRING user in Bolivia wants to personalize the Spring “datum” file for using the UTM projection. It is possible to use the WGS-84 as a reference and define the translations for the local datum, PSAD-56, referred to the WGS-84. Remember that the UTM projection has identifier 1. The edited file can have the lines presented below. In this example the Bolivian user that selects an UTM projection has the Earth Models WGS-84 and PSAD-56 available, as well as the Hayford and Clarke ellipsoids. 1 WGS84 6.378137e+06 3.352811e-03 0.000000e+00 0.000000e+00 0.000000e+00 1 PSAD56 6.378388e+06 3.367003e-03 -2.700000e+02 1.880000e+02 -3.880000e+02 1 Hayford 6.378388e+06 3.367003e-03 0.000000e+00 0.000000e+00 0.000000e+00 1 Clarke 6.378206e+06 3.390060e-03 0.000000e+00 0.000000e+00 0.000000e+00 It is wisely to remember that the translations have to be inserted carefully to guarantee that SPRING makes the datum change for the new one adequately. That is because it is important to use the official parameters computed by the Geodesy and Cartographical offices in each country. The changes performed for a certain projection can be repeated for other projections as far as the parameters are changed adequately. Remember, also, that all other lines with the identifiers for other projections and datum parameters must be kept in the “datum” structure file. Finally, keep the edited file with the same name without extension.
![]() |