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 (a) and gain (b), residuals (R),
number of elements (N), medians (medX, medY), standard deviations
(sdX, sdY), and the F test for testing the significance of the
regression model as a whole (F).
EXAMPLE
Comparison of the old and the new DEM in Spearfish: