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## NAME

r.regression.line - Calculates linear regression from two raster maps: y = a + b*x.

## KEYWORDS

raster, statistics

## SYNOPSIS

r.regression.line
r.regression.line help
r.regression.line [-gs] map1=name map2=name [output=name] [--verbose] [--quiet]

### Flags:

-g
Print in shell script style
-s
This does nothing. It is retained for backwards compatibility
--verbose
Verbose module output
--quiet
Quiet module output

### Parameters:

map1=name
Map for x coefficient
map2=name
Map for y coefficient
output=name
ASCII file for storing regression coefficients (output to screen if file not specified).

## DESCRIPTION

r.regression.line Calculates linear regression from two raster maps, according to the formula y = a + b*x, where x and y represent raster maps. Optionally saves regression coefficients to an 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 the old and the new DEM in Spearfish:
g.region rast=elevation.10m -p
r.regression.line map1=elevation.dem map2=elevation.10m

Using the script style flag AND eval to make results available in the shell:

g.region rast=elevation.10m -p
eval `r.regression.line -g map1=elevation.dem map2=elevation.10m`
echo \$a
479.615

echo \$b
0.645631

echo \$R
0.804441

## AUTHOR

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

Last changed: \$Date: 2013-09-13 19:52:51 -0700 (Fri, 13 Sep 2013) \$