This is the command r.regression.linegrass that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
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
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