.TH r.regression.line 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBr.regression.line\fR\fR  \- Calculates linear regression from two raster maps: y = a + b*x.
.SH KEYWORDS
raster, statistics, regression
.SH SYNOPSIS
\fBr.regression.line\fR
.br
\fBr.regression.line \-\-help\fR
.br
\fBr.regression.line\fR [\-\fBg\fR] \fBmapx\fR=\fIname\fR \fBmapy\fR=\fIname\fR  [\fBoutput\fR=\fIname\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-g\fR" 4m
.br
Print in shell script style
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBmapx\fR=\fIname\fR \fB[required]\fR" 4m
.br
Map for x coefficient
.IP "\fBmapy\fR=\fIname\fR \fB[required]\fR" 4m
.br
Map for y coefficient
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
ASCII file for storing regression coefficients (output to screen if file not specified).
.SH DESCRIPTION
\fIr.regression.line\fR calculates a linear regression from two
raster maps, according to the formula
.br
.nf
\fC
y = a + b*x
\fR
.fi
where
.br
.nf
\fC
x
y
\fR
.fi
represent the input raster maps.
.PP
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).
.SH NOTES
The results for offset/intercept (a) and gain/slope (b) are
identical to that obtained from R\-stats\(cqs lm() function.
.SH EXAMPLE
Comparison of two DEMs (SRTM and NED, both at 30m resolution),
provided in the North Carolina sample dataset:
.br
.nf
\fC
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
\fR
.fi
.PP
Using the script style flag AND \fIeval\fR to make results
available in the shell:
.br
.nf
\fC
g.region raster=elev_srtm_30m \-p
eval \(gar.regression.line \-g mapx=elev_ned_30m mapy=elev_srtm_30m\(ga
# print result stored in respective variables
echo $a
\-1.659279
echo $b
1.043968
echo $R
0.894038
\fR
.fi
.SH SEE ALSO
\fI
d.correlate,
r.regression.multi,
r.stats
\fR
.SH AUTHORS
Dr. Agustin Lobo \- alobo at ija.csic.es
.br
Updated to GRASS 5.7 Michael Barton, Arizona State University
.br
Script style output Markus Neteler
.br
Conversion to C module Markus Metz
.SH SOURCE CODE
.PP
Available at: r.regression.line source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual