gdallocationinfo: gdallocationinfo

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

Description

R wrapper for gdallocationinfo: raster query tool

Usage

gdallocationinfo(
  srcfile,
  x,
  y,
  coords,
  xml,
  lifonly,
  valonly,
  b,
  overview,
  l_srs,
  geoloc,
  wgs84,
  oo,
  raw_output = TRUE,
  ignore.full_scan = TRUE,
  verbose = FALSE
)

Arguments

srcfile	Character. The source GDAL raster datasource name.
x	Numeric. X location of target pixel. By default the coordinate system is pixel/line unless -l_srs, -wgs84 or -geoloc supplied.
y	Numeric. Y location of target pixel. By default the coordinate system is pixel/line unless -l_srs, -wgs84 or -geoloc supplied.
coords	Character or Matrix. Filename of coordinates (space separated, no header) or a matrix of coordinates.
xml	Logical. The output report will be XML formatted for convenient post processing.
lifonly	Logical. The only output is filenames production from the LocationInfo request against the database (ie. for identifying impacted file from VRT).
valonly	Logical. The only output is the pixel values of the selected pixel on each of the selected bands.
b	Numeric. band. Selects a band to query. Multiple bands can be listed. By default all bands are queried.
overview	Numeric. overview_level. Query the (overview_level)th overview (overview_level=1 is the 1st overview), instead of the base band. Note that the x,y location (if the coordinate system is pixel/line) must still be given with respect to the base band.
l_srs	Character. srs def. The coordinate system of the input x, y location.
geoloc	Logical. Indicates input x,y points are in the georeferencing system of the image.
wgs84	Logical. Indicates input x,y points are WGS84 long, lat.
oo	Character. "NAME=VALUE". (starting with GDAL 2.0) Dataset open option (format specific)
raw_output	Logical. Dump the raw output of the gdallocationinfo (default=TRUE). If not, attempt to return a matrix of data.
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.

Details

This is an R wrapper for the 'gdallocationinfo' 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 gdalinfo format (http://www.gdal.org/gdallocationinfo.html), or, in some cases, use R vectors to achieve the same end.

This utility is intended to provide a variety of information about a pixel. Currently it reports three things:

The location of the pixel in pixel/line space. The result of a LocationInfo metadata query against the datasource - currently this is only implemented for VRT files which will report the file(s) used to satisfy requests for that pixel. The raster pixel value of that pixel for all or a subset of the bands. The unscaled pixel value if a Scale and/or Offset apply to the band. The pixel selected is requested by x/y coordinate on the commandline, or read from stdin. More than one coordinate pair can be supplied when reading coordinatesis from stdin. By default pixel/line coordinates are expected. However with use of the -geoloc, -wgs84, or -l_srs switches it is possible to specify the location in other coordinate systems.

The default report is in a human readable text format. It is possible to instead request xml output with the -xml switch.

For scripting purposes, the -valonly and -lifonly switches are provided to restrict output to the actual pixel values, or the LocationInfo files identified for the pixel.

It is anticipated that additional reporting capabilities will be added to gdallocationinfo in the future.

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.

Value

Character or matrix (if valonly=T & raw_output=F)

Author(s)

Jonathan A. Greenberg ([e-mail]) (wrapper) and Frank Warmerdam (GDAL lead developer).

References

http://www.gdal.org/gdallocationinfo.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(valid_install)
{
	src_dataset <- system.file("external/tahoe_highrez.tif", package="gdalUtils")
	# Raw output of a single coordinate:
	gdallocationinfo(srcfile=src_dataset,x=10,y=10)

	# A matrix of coordinates and a clean, matrix output:
	coords <- rbind(c(10,10),c(20,20),c(30,30))
	gdallocationinfo(srcfile=src_dataset,coords=coords,valonly=TRUE,raw_output=FALSE)
}

gearslaboratory/gdalUtils documentation built on Feb. 17, 2020, 8:09 a.m.