## NAME

r.regression.line

## 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 (Mon, 28 Jan 2008) $

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