r.regression.line(1grass) GRASS GIS User's Manual r.regression.line(1grass)
NAME
r.regression.line - Calculates linear regression from two raster maps:
y = a + b*x.
KEYWORDS
raster, statistics, regression
SYNOPSIS
r.regression.line
r.regression.line --help
r.regression.line [-g] mapx=name mapy=name [output=name] [--over-
write] [--help] [--verbose] [--quiet] [--ui]
Flags:
-g
Print in shell script style
--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:
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).
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 re-
sult 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 script style flag AND eval to make results available in the
shell:
g.region raster=elev_srtm_30m -p
eval `r.regression.line -g mapx=elev_ned_30m mapy=elev_srtm_30m`
# print result stored in respective variables
echo $a
-1.659279
echo $b
1.043968
echo $R
0.894038
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)
Accessed: unknown
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GRASS 7.8.7 r.regression.line(1grass)
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