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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

SEE ALSO

        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

       Last changed: $Date: 2015-10-27 18:40:48 +0100 (Tue, 27 Oct 2015) $

SOURCE CODE

       Available at: r.regression.line source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual