R/projpar.R

In pobsteta/theia2r: An R toolbox to find, download and preprocess Sentinel-2 data

#' @title Return a parameter used in a WRT projection
#' @description Return the value of a parameter (or the name) present in
#'  the WKT of the given proj4string.
#' @param proj4string The proj4string to be named (a character or a [CRS]
#'  object).
#' @param par Character corresponding to the parameter name.
#' @param abort logical: if TRUE, the function aborts in case an invalid
#'  proj4string is passed; if FALSE (default), the function returns NA,
#'  and a warning is shown.
#' @return A character with the content of the parameter (NULL if the
#'  parameter is not recognised) or the name of the projection, and an
#'   attribute `proj4string` with the input projection checked using
#'  [sf::st_crs()].
#'
#' @author Luigi Ranghetti, phD (2017) \email{ranghetti.l@@irea.cnr.it}
#' @note Python is needed.
#' @export
#' @importFrom reticulate r_to_py py_to_r
#' @importFrom sf st_as_text st_crs
#' @importFrom magrittr '%>%'
#'
#' @examples \dontrun{
#' projpar('+init=epsg:4326', 'Unit')
#' }

projpar <- function(proj4string, par, abort = FALSE) {
    
    # import python modules
    py <- init_python()
    
    crs_check <- tryCatch(st_crs2(proj4string), error = function(e) {
        st_crs(NA)
    })
    
    if (is.na(crs_check$proj4string)) {
        return(NA)
    }
    
    proj4_wkt <- st_as_text(crs_check) %>% r_to_py() %>% py$osr$SpatialReference()
    proj4_par <- proj4_wkt$GetAttrValue(par) %>% py_to_r()
    
    attr(proj4_par, "proj4string") <- crs_check$proj4string
    
    return(proj4_par)
    
}


#' @name projname
#' @rdname projpar
#' @export
#' @importFrom sp is.projected CRS
#' @examples \dontrun{
#' projname('+init=epsg:4326')
#' }

projname <- function(proj4string, abort = FALSE) {
    
    proj4_name <- projpar(proj4string, "geogcs")
    
    if (is.projected(CRS(attr(proj4_name, "proj4string")))) {
        proj4_name <- projpar(proj4string, "projcs")
    }
    proj4_name <- gsub("\\_", " ", proj4_name)
    
    return(proj4_name)
    
}