Provided by: grass-doc_7.0.3-1build1_all 
NAME
r.univar - Calculates univariate statistics from the non-null cells of a raster map.
Statistics include number of cells counted, minimum and maximum cell values, range, arithmetic mean,
population variance, standard deviation, coefficient of variation, and sum.
KEYWORDS
raster, statistics, univariate statistics, zonal statistics
SYNOPSIS
r.univar
r.univar --help
r.univar [-get] map=name[,name,...] [zones=name] [output=name] [percentile=float[,float,...]]
[separator=character] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
-g
Print the stats in shell script style
-e
Calculate extended statistics
-t
Table output format instead of standard output format
--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 raster map(s)
zones=name
Raster map used for zoning, must be of type CELL
output=name
Name for output file (if omitted or "-" output to stdout)
percentile=float[,float,...]
Percentile to calculate (requires extended statistics flag)
Options: 0-100
Default: 90
separator=character
Field separator
Special characters: pipe, comma, space, tab, newline
Default: pipe
DESCRIPTION
r.univar calculates the univariate statistics of one or several raster map(s). This includes the number
of cells counted, minimum and maximum cell values, range, arithmetic mean, population variance, standard
deviation, coefficient of variation, and sum. Statistics are calculated separately for every
category/zone found in the zones input map if given. If the -e extended statistics flag is given the 1st
quartile, median, 3rd quartile, and given percentile are calculated. If the -g flag is given the results
are presented in a format suitable for use in a shell script. If the -t flag is given the results are
presented in tabular format with the given field separator. The table can immediately be converted to a
vector attribute table which can then be linked to a vector, e.g. the vector that was rasterized to
create the zones input raster.
When multiple input maps are given to r.univar, the overall statistics are calculated. This is useful for
a time series of the same variable, as well as for the case of a segmented/tiled dataset. Allowing
multiple raster maps to be specified saves the user from using a temporary raster map for the result of
r.series or r.patch.
NOTES
As with most GRASS raster modules, r.univar operates on the raster array defined by the current region
settings, not the original extent and resolution of the input map. See g.region.
This module can use large amounts of system memory when the -e extended statistics flag is used with a
very large region setting. If the region is too large the module should exit gracefully with a memory
allocation error. Basic statistics can be calculated using any size input region.
Without a zones input raster, the r.quantile module will be significantly more efficient for calculating
percentiles with large maps.
For calculating univariate statistics from a raster map based on vector polygon map and uploads
statistics to new attribute columns, see v.rast.stats.
EXAMPLE
In this example, the raster polygon map basins in the North Carolina sample dataset is used to calculate
raster statistics for zones for elevation raster map:
g.region raster=basins -p
This will set and print computational region in the format:
projection: 99 (Lambert Conformal Conic)
zone: 0
datum: nad83
ellipsoid: a=6378137 es=0.006694380022900787
north: 228500
south: 215000
west: 630000
east: 645000
nsres: 10
ewres: 10
rows: 1350
cols: 1500
cells: 2025000
Check basin’s IDs using:
r.category basins
This will print them in the format:
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
Visualization of them underlying elevation map can be created as:
d.mon wx0
d.rast map=elevation
r.colors map=elevation color=grey
d.rast map=basins
r.colors map=basins color=bgyr
d.legend raster=basins use=2,4,6,8,10,12,14,16,18,20,22,24,26,28,30
d.barscale
Figure: Zones (basins, opacity: 60%) with underlying elevation map for North Carolina sample dataset.
Then statistics for elevation can be calculated separately for every zone, i.e. basin found in the zones
parameter:
r.univar -t map=elevation zones=basins separator=comma \
output=basin_elev_zonal.csv
This will print information in the format:
zone,label,non_null_cells,null_cells,min,max,range,mean,mean_of_abs,
stddev,variance,coeff_var,sum,sum_abs2,,116975,0,55.5787925720215,
133.147018432617,77.5682258605957,92.1196971445722,92.1196971445722,
15.1475301152556,229.447668592576,16.4433129773355,10775701.5734863,
10775701.57348634,,75480,0,61.7890930175781,110.348838806152,
48.5597457885742,83.7808205765268,83.7808205765268,11.6451777476995,
135.610164775515,13.8995747088232,6323776.33711624,6323776.33711624
6,,1137,0,66.9641571044922,83.2070922851562,16.2429351806641,
73.1900814395257,73.1900814395257,4.15733292896409,17.2834170822492,
5.68018623179036,83217.1225967407,83217.12259674078,,80506,
0,67.4670791625977,147.161514282227, ...
Comma Separated Values (CSV) file is best viewed through a spreadsheet program such as Microsoft Excel,
Libre/Open Office Calc or Google Docs:
Figure: Raster statistics for zones (basins, North Carolina sample dataset) viewed through Libre/Open
Office Calc
TODO
To be implemented mode, skewness, kurtosis.
SEE ALSO
g.region, r3.univar, r.mode, r.quantile, r.series, r.stats, r.stats.quantile, r.stats.zonal,
r.statistics, v.rast.stats, v.univar
AUTHORS
Hamish Bowman, Otago University, New Zealand
Extended statistics by Martin Landa
Multiple input map support by Ivan Shmakov
Zonal loop by Markus Metz
Last changed: $Date: 2015-09-02 13:27:57 +0200 (Wed, 02 Sep 2015) $
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