R/gdal_formats_db.R

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

#' @title Create the database of GDAL supported formats
#' @description The internal function checks if gdal_formats.json (the
#'  database of spectral indices) already exists; if not, it
#'  downloads source files and creates it.
#'  Since on Windows there is an issue in reading the extension of 
#'  a GDAL driver with `reticulate` functions when the package `theia2r`
#'  was already charged, this function can be used only from from
#'  Linux. It is not necessary, since a gdal_formats.json file is
#'  present in the package, but can be used to update the list in accordance
#'  with the formats actually managed by your GDAl installation.
#' @param json_path (optional) The path of the output JSON file.
#'  *Warning*: to create a file which wil be usable by the package,
#'  this option must be left to NA (default location is within the
#'  package installation). Edit this only to create the file in another
#'  place for external use.
#' @param force (optional) Logical: if FALSE (default), the db is created only
#'  if missing or not updated; if TRUE, it is created in any case..
#' @return NULL
#' @author Luigi Ranghetti, phD (2017) \email{ranghetti.l@@irea.cnr.it}
#' @note License: GPL 3.0
#' @importFrom reticulate py_to_r
#' @importFrom jsonlite toJSON fromJSON
#' @importFrom rgdal gdalDrivers
#' @importFrom utils packageVersion

gdal_formats_db <- function(json_path = NA, force = FALSE) {
    
    # check if gdal_formats.json already exists, and if the version is updated we assume that a new version of gdal_formats.json is created at every new package update
    if (is.na(json_path)) {
        json_path <- file.path(system.file("extdata", package = "theia2r"), "gdal_formats.json")
    }
    if (system.file("extdata", "gdal_formats.json", package = "theia2r") == json_path) {
        json_version <- jsonlite::fromJSON(json_path)$pkg_version %>% package_version()
        if (force == FALSE & json_version >= packageVersion("theia2r")) {
            return(invisible(NULL))
        }
    }
    
    # load python modules
    py <- init_python()
    
    # read GDAL drivers
    gdal_driver_list <- list()
    for (i in seq_len((py_to_r(gdal$GetDriverCount()) - 1))) {
        gdal_driver_list[[i]] <- py$gdal$GetDriver(py$py$int(i))
    }
    
    # export vectors of names and extensions
    gdal_driver_ext <- sapply(gdal_driver_list, function(x) {
        unlist(strsplit(paste0(py_to_r(x$GetMetadataItem(py$gdal$DMD_EXTENSIONS)), " "), " "))[1]
    })
    gdal_driver_names <- sapply(gdal_driver_list, function(x) {
        py_to_r(x$ShortName)
    })
    gdal_driver_namext <- data.frame(name = gdal_driver_names, ext = gdal_driver_ext, stringsAsFactors = FALSE)
    
    # read other information using rgdal
    gdal_drivers <- gdalDrivers()
    
    gdal_drivers <- merge(gdal_drivers, gdal_driver_namext, by = "name", all.x = TRUE)
    
    # fix specific formats
    gdal_drivers[gdal_drivers$name == "VRT", "ext"] <- "vrt"
    gdal_drivers[gdal_drivers$name == "ENVI", "ext"] <- "dat"
    
    ## Convert in JSON
    writeLines(jsonlite::toJSON(gdal_drivers, pretty = TRUE), json_path)
    return(invisible(NULL))
    
}