ABSTRACT
The set of information that defined shape, size, origin and orientation of coordinate systems established for positioning points on the Earth's surface defined a geodetic datum. Geodetic surveys have been used to establish horizontal and vertical accuracy of reference monuments and serve as the basis for generating or checking existing survey designs. In the computing practice, coordinate reference systems (CRSs) are applied to spatial points with attribute data, referring to vector point surveyed vertices, or to raster data, referring to georeferenced orthoimagery from aerial or orbital surveys. CRS can be described in R by a European Petroleum Survey Group (EPSG) code or a definition of proj4string. Using R packages, it is possible to evaluate a wide variety of CRS. This enables to check and assign a coordinate system to point attribute vector type data, determine the Euclidean distance and compare with geodetic and spherical distance between vertices. Calculations of plane, geodetic and spherical areas are performed. Area determinations in SIRGAS-2000, SAD-69, Chua and Córrego Alegre 1961 ellipsoids in Brazil are compared. A digital elevation model Shuttle Radar Topography Mission (SRTM) is used as an example of transformation of geographic projection WGS-84 to SIRGAS-2000 in a raster type file.
