GRASS GIS manual: r.what

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here

NAME

r.what - Queries raster maps on their category values and category labels.

KEYWORDS

raster, querying, position

SYNOPSIS

r.what

r.what --help

r.what [-nfric] map=name[,name,...] [coordinates=east,north] [points=name] [null_value=string] [output=name] [separator=character] [cache=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-n: Output header row
-f: Show the category labels of the grid cell(s)
-r: Output color values as RRR:GGG:BBB
-i: Output integer category values, not cell values
-c: Turn on cache reporting
--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

map=name[,name,...] [required]: Name of existing raster map(s) to query
coordinates=east,north: Coordinates for query
points=name: Name of vector points map for query; Or data source for direct OGR access
null_value=string: String representing NULL value; Default: *
output=name: Name for output file (if omitted or "-" output to stdout)
separator=character: Field separator; Special characters: pipe, comma, space, tab, newline; Default: pipe
cache=integer: Size of point cache; Default: 500

DESCRIPTION
EXAMPLES
NOTE
TODO
SEE ALSO
AUTHOR

DESCRIPTION

r.what outputs the category values and (optionally) the category labels associated with user-specified locations on raster input map(s). Locations are specified as geographic x,y coordinate pairs (i.e., pair of eastings and northings); the user can also (optionally) associate a label with each location.

The input coordinates can be entered directly on the command line via coordinates parameter, or redirected via stdin from an input text file, script, or piped from another program (like v.out.ascii). Coordinates can be given also as a vector points map (points).

If none of the above input methods are used and the module is run from the terminal prompt, the program will interactively query the user for point locations and labels.

Each line of the input consists of an easting, a northing, and an optional label, which are separated by spaces. In interactive mode, the word "end" must be typed after the last pair of input coordinates.

r.what output consists of the input geographic location and label, and, for each user-named raster map layer, the category value, and (if the -f label flag is specified) the category label associated with the cell(s) at this geographic location.

EXAMPLES

Input coordinates given as an option

The module's coordinates parameter can be used to enter coordinate pairs directly. The maximum number of pairs will be limited by your system's maximum input line length (e.g. 4096 characters).

g.region raster=landuse96_28m,aspect -p
r.what map=landuse96_28m,aspect coordinates=633614.08,224125.12,632972.36,225382.87 -f

633614.08|224125.12||2|Low Intensity Developed|209.5939|209 degrees ccw from east
632972.36|225382.87||15|Southern Yellow Pine|140.7571|140 degrees ccw from east

Input coordinates given as a vector points map

Coordinates can be read from existing vector points map by specifying points option. Other features than points or centroids are ignored. Example: query North Carolina county number for each community college:

g.region raster=boundary_county_500m -p
r.what map=boundary_county_500m points=comm_colleges

145096.859150|154534.264884||39
616341.437150|146049.750884||51
...

Input coordinates given as a vector points map, output into CSV file

Coordinates can be read from existing vector points map by specifying points option. Other features than points or centroids are ignored. The output is stored in a CSV file including header row. Example: query North Carolina county number for each community college:

g.region raster=boundary_county_500m -p
r.what map=boundary_county_500m points=comm_colleges \
       separator=comma output=result.csv -n
       
cat result.csv 
easting,northing,site_name,boundary_county_500m
145096.859150,154534.264884,,39
616341.437150,146049.750884,,51
410595.719150,174301.828884,,71
...

Input from a text file containing coordinates

The contents of an ASCII text file can be redirected to r.what as follows. If we have a file called input_coord.txt containing the whitespace separated coordinates and optionally labels, the resulting raster map values are extracted:

cat input_coord.txt 
633614.08 224125.12 site 1
632972.36 225382.87 site 2

r.what map=landuse96_28m,aspect < input_coord.txt

633614.08|224125.12|site 1|2|209.5939
632972.36|225382.87|site 2|15|140.7571

Input from standard input on the command line

Input coordinates may be given directly from standard input (stdin), for example (input data appears between the "EOF" markers):

r.what map=landuse96_28m,aspect << EOF
633614.08 224125.12 site 1
632972.36 225382.87 site 2
EOF

633614.08|224125.12|site 1|2|209.5939
632972.36|225382.87|site 2|15|140.7571

echo "633614.08 224125.12" | r.what map=landuse96_28m,aspect

633614.08|224125.12||2|209.5939

Input coordinates piped from another program

The input coordinates may be "piped" from the standard output (stdout) of another program. In the next example, vector point coordinates are piped from the v.out.ascii module.

v.out.ascii comm_colleges separator=space | r.what map=boundary_county_500m

145096.8591495|154534.26488388|1|39
616341.4371495|146049.75088388|2|51
410595.7191495|174301.82888388|3|71
...

Output containing raster map category labels

Here we use the -f label flag to enable the output of category labels associated with the raster cell(s), as well as values (categorical maps only).

r.what -f map=landuse96_28m,aspect << EOF
633614.08 224125.12 site 1
632972.36 225382.87 site 2
EOF

633614.08|224125.12|site 1|2|Low Intensity Developed|209.5939|209 degrees ccw from east
632972.36|225382.87|site 2|15|Southern Yellow Pine|140.7571|140 degrees ccw from east

NOTE

The maximum number of raster map layers that can be queried at one time is 400.

TODO

Fix 400 maps limit

AUTHOR

Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
Vector point input added by Martin Landa, Czech Technical University in Prague, Czech Republic

Last changed: $Date: 2016-03-08 00:08:23 -0800 (Tue, 08 Mar 2016) $

SOURCE CODE

Available at: r.what source code (history)