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r.regression.line.1grass

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=string map2=string [output=string] [--verbose] [--quiet]

Flags:

-g

Print in shell script style

-s

Slower but accurate (applies to FP maps only)

--verbose

Verbose module output

--quiet

Quiet module output

Parameters:

map1=string

Map for x coefficient

map2=string

Map for y coefficient

output=string

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), residuals (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 flag -s select the slower method (applies to FP maps only) which writes out all pixel values individually to the temporary file. The results for offset/intercept (a) and gain/slope (b) are then 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

Last changed: $Date: 2008-01-28 09:24:54 +0100 (lun, 28 gen 2008) $

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