Global 2.5 Minute Geoid Undulations, a big raster from multiple files. We just create a temporary virtual raster from the source files, and return as a RasterLayer.
read_geoid(xylim = NULL, force = FALSE)an extent, in longlat, or an object that provides one
if TRUE ignore cached virtual saved file, and recompute (try this if it otherwise fails)
RasterLayer, longitude latitue grid of geoid level
Each file is an ESRI GRID raster data set of 2.5-minute geoid undulation values covering a 45 x 45 degree area. Each raster file has a 2.5-minute cell size and is a subset of the global 2.5 x 2.5-minute grid of pre-computed geoid undulation point values found on the EGM2008-WGS 84 Version web page. This ESRI GRID format represents a continuous surface of geoid undulation values where each 2.5-minute raster cell derives its value from the original pre-computed geoid undulation point value located at the SW corner of each cell.
if (FALSE) {
geoid <- read_geoid()
}