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#' gdal_contour
#'
#' R wrapper for gdal_contour: builds vector contour lines from a raster elevation model
#'
#' @param src_filename Character. Any OGR supported readable datasource.
#' @param dst_filename Character. The OGR supported output file.
#' @param b Numeric. Picks a particular band to get the DEM from. Defaults to band 1.
#' @param a Character. Provides a name for the attribute in which to put the elevation. If not provided no elevation attribute is attached.
#' @param threeD Logical. (GDAL parameter '3d') Force production of 3D vectors instead of 2D. Includes elevation at every vertex.
#' @param inodata Logical. Ignore any nodata value implied in the dataset - treat all values as valid.
#' @param snodata Numeric. Input pixel value to treat as "nodata".
#' @param f Character. Create output in a particular format, default is "ESRI Shapefiles".
#' @param dsco Character. Dataset creation option (format specific). Follows "NAME=VALUE" format.
#' @param lco Character. Layer creation option (format specific). Follows "NAME=VALUE" format.
#' @param i Numeric. Elevation interval between contours.
#' @param off Numeric. Offset from zero relative to which to interpret intervals.
#' @param fl Character. Name one or more "fixed levels" to extract.
#' @param nln Character. Provide a name for the output vector layer. Defaults to "contour".
#' @param output_Vector Logical. Return output dst_filename as a Spatial* object. Currently only works with f="ESRI Shapefile".
#' @param config Character. Sets runtime configuration options for GDAL. See https://trac.osgeo.org/gdal/wiki/ConfigOptions for more information.
#' @param ignore.full_scan Logical. If FALSE, perform a brute-force scan if other installs are not found. Default is TRUE.
#' @param verbose Logical. Enable verbose execution? Default is FALSE.
#' @return output vector filename or SpatialLinesDataFrame object.
#' @author Jonathan A. Greenberg (\email{gdalUtils@@estarcion.net}) (wrapper) and Frank Warmerdam (GDAL lead developer).
#' @details This is an R wrapper for the 'gdal_contour' function that is part of the
#' Geospatial Data Abstraction Library (GDAL). It follows the parameter naming
#' conventions of the original function, with some modifications to allow for more R-like
#' parameters. For all parameters, the user can use a single character string following,
#' precisely, the gdal_contour format (\url{http://www.gdal.org/gdal_contour.html}), or,
#' in some cases, can use R vectors to achieve the same end.
#'
#' This function assumes the user has a working GDAL on their system. If the
#' "gdalUtils_gdalPath" option has been set (usually by gdal_setInstallation),
#' the GDAL found in that path will be used. If nothing is found, gdal_setInstallation
#' will be executed to attempt to find a working GDAL that has the right drivers
#' as specified with the "of" (output format) parameter.
#'
#' The user can choose to (optionally) return a RasterBrick of the output file (assuming
#' raster/rgdal supports the particular output format).
#'
#' @references \url{http://www.gdal.org/gdal_contour.html}
#' @examples
#' # We'll pre-check to make sure there is a valid GDAL install
#' # and that raster and rgdal are also installed.
#' # Note this isn't strictly neccessary, as executing the function will
#' # force a search for a valid GDAL install.
#' gdal_setInstallation()
#' valid_install <- !is.null(getOption("gdalUtils_gdalPath"))
#' if(require(raster) && require(rgdal) && valid_install)
#' {
#' # Example from the original gdal_contour documentation:
#' # gdal_contour -a elev dem.tif contour.shp -i 10.0
#' # Choose a DEM:
#' input_dem <- system.file("external/tahoe_lidar_bareearth.tif", package="gdalUtils")
#' # Setup an output filename (shapefile):
#' output_shapefile <- paste(tempfile(),".shp",sep="")
#' contour_output <- gdal_contour(src_filename=input_dem,dst_filename=output_shapefile,
#' a="Elevation",i=5.,output_Vector=TRUE)
#' # Plot the contours using spplot:
#' spplot(contour_output["Elevation"],contour=TRUE)
#' }
#' @import rgdal
#' @export
gdal_contour <- function(
src_filename,dst_filename,
b,a,threeD,inodata,snodata,i,
f="ESRI Shapefile",
dsco,lco,off,fl,nln,
output_Vector=FALSE,
config,
ignore.full_scan=TRUE,
verbose=FALSE)
{
if(output_Vector && (!requireNamespace("rgdal")))
{
warning("rgdal not installed. Please install.packages('rgdal') or set output_Vector=FALSE")
return(NULL)
}
parameter_values <- as.list(environment())
if(verbose) message("Checking gdal_installation...")
gdal_setInstallation(ignore.full_scan=ignore.full_scan)
if(is.null(getOption("gdalUtils_gdalPath"))) return()
# Place all gdal function variables into these groupings:
parameter_variables <- list(
logical = list(
varnames <- c(
"threeD","inodata"
)),
vector = list(
varnames <- c(
)),
scalar = list(
varnames <- c(
"b","snodata","i","off"
)),
character = list(
varnames <- c(
"a","f","fl","nln","src_filename","dst_filename"
)),
repeatable = list(
varnames <- c(
"dsco","lco","config"
))
)
parameter_order <- c(
"b","a","threeD","inodata","snodata",
"f","dsco","lco","i","off","fl","nln",
"src_filename","dst_filename","config"
)
parameter_noflags <- c("src_filename","dst_filename")
parameter_noquotes <- unlist(parameter_variables$vector)
parameter_doubledash <- c("config")
executable <- "gdal_contour"
cmd <- gdal_cmd_builder(
executable=executable,
parameter_variables=parameter_variables,
parameter_values=parameter_values,
parameter_order=parameter_order,
parameter_noflags=parameter_noflags,
parameter_noquotes=parameter_noquotes,
parameter_doubledash=parameter_doubledash,
# gdal_installation_id=gdal_chooseInstallation(hasDrivers=of))
gdal_installation_id=gdal_chooseInstallation())
if(verbose) message(paste("GDAL command being used:",cmd))
cmd_output <- system(cmd,intern=TRUE)
if(output_Vector && f=="ESRI Shapefile")
{
return(
readOGR(dsn=dirname(dst_filename),
layer=remove_file_extension(basename(dst_filename)))
)
# return(brick(dst_filename))
} else
{
return(dst_filename)
}
}
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