name: r.regression.line description: Calculates linear regression from two raster maps: y = a + b*x. keywords: [ raster, statistics, regression ]
r.regression.line
Calculates linear regression from two raster maps: y = a + b*x.
r.regression.line [-g] mapx=name mapy=name [output=name] format=name [--overwrite] [--verbose] [--quiet] [--qq] [--ui]
Example:
r.regression.line mapx=name mapy=name format=plain
grass.script.parse_command("r.regression.line", mapx, mapy, output=None, format="plain", flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)
Example:
gs.parse_command("r.regression.line", mapx="name", mapy="name", format="json")
Parameters
mapx=name [required]
Map for x coefficient
mapy=name [required]
Map for y coefficient
output=name
ASCII file for storing regression coefficients (output to screen if file not specified).
format=name [required]
Output format
Allowed values: plain, shell, json
Default: plain
plain: Human readable text output
shell: shell script style text output
json: JSON (JavaScript Object Notation)
-g
Print in shell script style [deprecated]
This flag is deprecated and will be removed in a future release. Use format=shell instead.
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--qq
Very quiet module output
--ui
Force launching GUI dialog
mapx : str, required
Map for x coefficient
Used as: input, raster, name
mapy : str, required
Map for y coefficient
Used as: input, raster, name
output : str, optional
ASCII file for storing regression coefficients (output to screen if file not specified).
Used as: output, file, name
format : str, required
Output format
Used as: name
Allowed values: plain, shell, json
plain: Human readable text output
shell: shell script style text output
json: JSON (JavaScript Object Notation)
Default: plain
flags : str, optional
Allowed values: g
g
Print in shell script style [deprecated]
This flag is deprecated and will be removed in a future release. Use format=shell instead.
overwrite: bool, optional
Allow output files to overwrite existing files
Default: False
verbose: bool, optional
Verbose module output
Default: False
quiet: bool, optional
Quiet module output
Default: False
superquiet: bool, optional
Very quiet module output
Default: False
DESCRIPTION
r.regression.line calculates a linear regression from two raster maps, according to the formula
y = a + b*x
where
x
y
represent the input raster maps.
Optionally, it saves regression coefficients as a ASCII file. The result includes the following coefficients: offset/intercept (a) and gain/slope (b), correlation coefficient (R), number of elements (N), means (medX, medY), standard deviations (sdX, sdY), and the F test for testing the significance of the regression model as a whole (F).
NOTES
The results for offset/intercept (a) and gain/slope (b) are identical to that obtained from R-stats's lm() function.
EXAMPLE
Comparison of two DEMs (SRTM and NED, both at 30m resolution), provided in the North Carolina sample dataset:
g.region raster=elev_srtm_30m -p
r.regression.line mapx=elev_ned_30m mapy=elev_srtm_30m
y = a + b*x
a (Offset): -1.659279
b (Gain): 1.043968
R (sumXY - sumX*sumY/N): 0.894038
N (Number of elements): 225000
F (F-test significance): 896093.366283
meanX (Mean of map1): 110.307571
sdX (Standard deviation of map1): 20.311998
meanY (Mean of map2): 113.498292
sdY (Standard deviation of map2): 23.718307
Using the shell format option AND eval to make results available in the shell:
g.region raster=elev_srtm_30m -p
eval `r.regression.line mapx=elev_ned_30m mapy=elev_srtm_30m format=shell`
# print result stored in respective variables
echo $a
-1.659279
echo $b
1.043968
echo $R
0.894038
Using the JSON format option and Python to parse the output:
import grass.script as gs
data = gs.parse_command(
"r.regression.line", mapx="elev_ned_30m", mapy="elev_srtm_30m", format="json"
)
print(data)
Possible JSON Output:
{
"a": -1.6592786233805945,
"b": 1.0439679629649166,
"R": 0.8940383063008781,
"N": 225000,
"F": 896093.366283,
"x_mean": 110.30757108713786,
"x_stddev": 20.311997672696272,
"y_mean": 113.49829166406644,
"y_stddev": 23.718306793642626
}
SEE ALSO
d.correlate, r.regression.multi, r.stats
AUTHORS
Dr. Agustin Lobo - alobo at ija.csic.es
Updated to GRASS 5.7 Michael Barton, Arizona State University
Script style output Markus Neteler
Conversion to C module Markus Metz
SOURCE CODE
Available at: r.regression.line source code
(history)
Latest change: Tuesday Jul 01 19:42:35 2025 in commit 4ae5cc2