r.what - GRASS manual
Author: GRASS Development Team
Description: r.what: Queries raster maps on their category values and category labels.
Keywords: raster, querying, position

## 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 [-nfricv] map=name[,name,...] [coordinates=east,north] [points=name] [null_value=string] [output=name] [separator=character] format=name [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
-v
  Show the category for vector points map
--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
format=name [required]
  Output format
  Options: plain, json
  Default: plain
  plain: Plain text output
  json: JSON (JavaScript Object Notation)
cache=integer
  Size of point cache
  Default: 500

## 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 with cats

Coordinates can be read from existing vector points map by specifying points option. Other features than points or centroids are ignored. Using the v flag you can get also the cat for each feature. 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 -v

    1|145096.859150|154534.264884||39
    2|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

## SEE ALSO

r.category, r.report, r.stats, r.series, r.univar, v.what, v.what.rast, v.what.vect

## AUTHORS

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

## SOURCE CODE

Available at: r.what source code (history)

Latest change: Monday Dec 22 18:07:47 2025 in commit: cd86ea812e29ba28776cf5a102bf59288f49ce41

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