RSAGA: SAGA Geoprocessing and Terrain Analysis

#' RSAGA: SAGA Geoprocessing and Terrain Analysis in R
#'
#' RSAGA provides direct access to SAGA GIS functions
#' including, for example, a comprehensive set
#' of terrain analysis algorithms for calculating local
#' morphometric properties (slope, aspect, curvature),
#' hydrographic characteristics (size, height, and
#' aspect of catchment areas), and other process-related
#' terrain attributes (potential incoming solar radiation,
#' topographic wetness index, and more).
#' In addition, (R)SAGA provides functions for importing
#' and exporting different grid file formats, and tools
#' for preprocessing grids, e.g. closing gaps or filling
#' sinks.
#'
#' RSAGA adds a framework for creating custom-defined
#' focal functions, e.g. specialized filter and terrain
#' attributes such as the topographic wind shelter index,
#' within R.  This framework can be used to apply predict
#' methods of fitted statistical models to stacks of grids
#' representing predictor variables.  Furthermore,
#' functions are provided for conveniently picking
#' values at point locations from a grid using kriging
#' or nearest neighbour interpolation.
#'
#' RSAGA requires SAGA GIS (versions 2.3.1 LTS - 9.7.2)
#' are currently supported) and its user-contributed
#' modules to be available on your computer. These
#' can be downloaded under GPL from
#' <https://sourceforge.net/projects/saga-gis/>.
#' Please check the help page for
#' [rsaga.env()] to make sure that RSAGA
#' can find your local installation of SAGA. You may
#' need to 'tell' RSAGA where to find SAGA GIS.
#'
#' Thanks to Olaf Conrad, Andre Ringeler and all the
#' other SAGA GIS developers and contributors of
#' this excellent geocomputing tool! Thanks to Rainer
#' Hurling, Johan van de Wauw, Massimo Di Stefano and
#' others for helping to adapt SAGA to and test it on
#' unix and Max OSX.
#'
#' @references Brenning, A., 2008. Statistical geocomputing combining R and
#'  SAGA: The example of landslide susceptibility analysis with
#'  generalized additive models. In J. Boehner, T. Blaschke and
#'  L. Montanarella (eds.), SAGA - Seconds Out (= Hamburger
#'  Beitraege zur Physischen Geographie und
#'  Landschaftsoekologie, vol. 19), p. 23-32.
#'
#'  Conrad, O., Bechtel, M., Bock, M., Dietrich, H., Fischer, E., Gerlitz, L., Wichmann,
#'  V., & Boehner, J. (2015). System for Automated Geoscientific Analyses (SAGA) v. 2.1.4.
#'  *Geoscientific Model Development*, 8, 1991-2007
#'
#' @author Alexander Brenning, Donovan Bangs and Marc Becker
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