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@@ -1,8 +1,18 @@
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<h2>DESCRIPTION</h2>
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-<em>r.regression.line</em> Calculates linear regression from two raster maps,
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-according to the formula y = a + b*x, where x and y represent raster maps.
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-Optionally saves regression coefficients to an ASCII file.
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+<em>r.regression.line</em> calculates a linear regression from two
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+raster maps, according to the formula
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+<div class="code"><pre>
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+y = a + b*x
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+</pre></div>
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+where
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+<div class="code"><pre>
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+x
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+y
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+</pre></div>
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+represent the input raster maps.
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+<p>
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+Optionally, it saves regression coefficients as a ASCII file.
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The result includes the following coefficients:
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offset/intercept (a) and gain/slope (b), correlation coefficient (R),
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number of elements (N), means (medX, medY), standard deviations
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@@ -15,29 +25,43 @@ identical to that obtained from R-stats's lm() function.
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<h2>EXAMPLE</h2>
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-Comparison of the old and the new DEM in Spearfish:
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+Comparison of two DEMs (SRTM and NED, both at 30m resolution),
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+provided in the North Carolina sample dataset:
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+
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<div class="code"><pre>
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-g.region raster=elevation.10m -p
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-r.regression.line map1=elevation.dem map2=elevation.10m
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+g.region raster=elev_srtm_30m -p
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+r.regression.line mapx=elev_ned_30m mapy=elev_srtm_30m
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+ y = a + b*x
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+ a (Offset): -1.659279
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+ b (Gain): 1.043968
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+ R (sumXY - sumX*sumY/N): 0.894038
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+ N (Number of elements): 225000
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+ F (F-test significance): 896093.366283
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+ meanX (Mean of map1): 110.307571
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+ sdX (Standard deviation of map1): 20.311998
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+ meanY (Mean of map2): 113.498292
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+ sdY (Standard deviation of map2): 23.718307
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</pre></div>
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<p>
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Using the script style flag AND <em>eval</em> to make results
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available in the shell:
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<div class="code"><pre>
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-g.region raster=elevation.10m -p
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-eval `r.regression.line -g map1=elevation.dem map2=elevation.10m`
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+g.region raster=elev_srtm_30m -p
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+eval `r.regression.line -g mapx=elev_ned_30m mapy=elev_srtm_30m`
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+
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+# print result stored in respective variables
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echo $a
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-479.615
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+-1.659279
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echo $b
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-0.645631
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+1.043968
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echo $R
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-0.804441
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+0.894038
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</pre></div>
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-<h2>AUTHOR</h2>
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+<h2>AUTHORS</h2>
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Dr. Agustin Lobo - alobo at ija.csic.es<br>
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Updated to GRASS 5.7 Michael Barton, Arizona State University<br>
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Markus Neteler