gdalUtils (version 2.0.1.5)

gdal_contour: gdal_contour

Description

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

Usage

gdal_contour(src_filename, dst_filename, b, a, threeD, inodata, snodata, i,
  f = "ESRI Shapefile", dsco, lco, off, fl, nln, output_Vector = FALSE,
  ignore.full_scan = TRUE, verbose = FALSE)

Arguments

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".

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.

Value

• output vector filename or SpatialLinesDataFrame object.

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 (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

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)
}

Run the code above in your browser using DataCamp Workspace