gdal_contour: gdal_contour
In gdalUtils: Wrappers for the Geospatial Data Abstraction Library (GDAL) Utilities

Description Usage Arguments Details Value Author(s) References Examples

R wrapper for gdal_contour: builds vector contour lines from a raster elevation model

gdal_contour(
  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
)

`src_filename`	Character. Any OGR supported readable datasource.
`dst_filename`	Character. The OGR supported output file.
`b`	Numeric. Picks a particular band to get the DEM from. Defaults to band 1.
`a`	Character. Provides a name for the attribute in which to put the elevation. If not provided no elevation attribute is attached.
`threeD`	Logical. (GDAL parameter '3d') Force production of 3D vectors instead of 2D. Includes elevation at every vertex.
`inodata`	Logical. Ignore any nodata value implied in the dataset - treat all values as valid.
`snodata`	Numeric. Input pixel value to treat as "nodata".
`i`	Numeric. Elevation interval between contours.
`f`	Character. Create output in a particular format, default is "ESRI Shapefiles".
`dsco`	Character. Dataset creation option (format specific). Follows "NAME=VALUE" format.
`lco`	Character. Layer creation option (format specific). Follows "NAME=VALUE" format.
`off`	Numeric. Offset from zero relative to which to interpret intervals.
`fl`	Character. Name one or more "fixed levels" to extract.
`nln`	Character. Provide a name for the output vector layer. Defaults to "contour".
`output_Vector`	Logical. Return output dst_filename as a Spatial* object. Currently only works with f="ESRI Shapefile".
`config`	Character. Sets runtime configuration options for GDAL. See https://trac.osgeo.org/gdal/wiki/ConfigOptions for more information.
`ignore.full_scan`	Logical. If FALSE, perform a brute-force scan if other installs are not found. Default is TRUE.
`verbose`	Logical. Enable verbose execution? Default is FALSE.

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 (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).

output vector filename or SpatialLinesDataFrame object.

Jonathan A. Greenberg (gdalUtils@estarcion.net) (wrapper) and Frank Warmerdam (GDAL lead developer).

http://www.gdal.org/gdal_contour.html

# 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)
}