Note: This document is for an older version of GRASS GIS that will be discontinued soon. You should upgrade, and read the current manual page.

## 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] [--overwrite] [--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 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 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
```

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: Monday Nov 18 20:15:32 2019 in commit: 1a1d107e4f6e1b846f9841c2c6fabf015c5f720d

© 2003-2023 GRASS Development Team, GRASS GIS 7.8.9dev Reference Manual