R/list_indices.R

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

#' @title List spectral indices
#' @description Return a table with attributes of the spectral indices
#'  computable with the package.
#' @param values A vector of attributes which will be returned, being
#'  one or more within the followings:
#'  - `n_index`: internal index identifiers;
#'  - `name`: index name;
#'  - `longname`: index description;
#'  - `link`: URL to the index description page;
#'  - `s2_formula`: expression containing the formula to compute the index;
#'  - `s2_formula_mathml`: MathML version of the formula;
#'  - `checked`: logical (TRUE for verified indices);
#'  - `a`, `b`, `x`: parameter values (NA for non required parameters).
#' @param pattern A regular expression on index names.
#' @return A data.frame with the required information. The table contains
#'  also the following attributes:
#'  - `creation_date`: timestamp of the creation date of the indices archive;
#'  - `pkg_version`: version of the `theia2r` package used to
#'      create the indices archive.
#' @export
#' @importFrom jsonlite fromJSON
#' @import data.table
#' @author Luigi Ranghetti, phD (2017) \email{ranghetti.l@@irea.cnr.it}
#' @note License: GPL 3.0
#' @examples \dontrun{
#' list_indices(c('name','longname'))
#' }

list_indices <- function(values, pattern = "") {
    
    # generate indices.json if missing
    create_indices_db()
    
    # read indices database
    json_path <- system.file("extdata", "indices.json", package = "theia2r")
    indices <- jsonlite::fromJSON(json_path)
    
    # select requested values from the table
    for (sel_par in c("a", "b", "x")) {
        if (is.null(indices$indices[[sel_par]])) {
            indices$indices[[sel_par]] <- as.numeric(NA)
        }
    }
    indices$indices <- indices$indices[grep(pattern, indices$indices$name), values]
    attr(indices$indices, "pkg_version") <- package_version(indices$pkg_version)
    attr(indices$indices, "creation_date") <- as.POSIXct(indices$creation_date)
    
    # return requested values
    return(indices$indices)
    
}