My suggestion is again to rewrite it a C program (not sure, based on r.univar code?). I found a couple of bugs in the script and I am (as you) not sure that it does what it promises to do).
Markus Nikos Alexandris wrote: > > I have submitted some comments upon the documentation of > the "r.regression.line" script in > http://wald.intevation.org/tracker/?func=detail&aid=552&group_id=21&atid=207 > > Now I have 2 questions. > > Apologies if I miss some obvious things but I am confused! > > Here it goes: > > 1. I don't understand why (in lines 84 and 85 in the > r.regression.line script) "sumsqX=sumsqX/tot" and > "sumsqY=sumsqY/tot" ? > > 2. I can't understand the differences in the following... : > I created two raster maps with the same MASK, each > containing only 6 pixels with the following values: > > mapA: 326 641 1336 2020 3197 3484 > mapB: 432 850 931 1956 2582 2622 > > For mapA "r.univar" gives: > n: 6 > minimum: 326 > maximum: 3484 > range: 3158 > mean: 1834 > mean of absolute values: 1834 > standard deviation: 1194.44 > variance: 1.4267e+06 > variation coefficient: 65.1278 % > sum: 11004) > > For mapB... : > n: 6 > minimum: 432 > maximum: 2622 > range: 2190 > mean: 1562.17 > mean of absolute values: 1562.17 > standard deviation: 866.145 > variance: 750207 > variation coefficient: 55.4451 % > sum: 9373) > > In openoffice calc (some of) the respective results are: > > For mapA: > MIN: 326 > MAX: 3484 > AVERAGE: 1834 > STDEV: 1308,45 > VAR: 1,71E+06 > SUM: 11004 > > For mapB: > MIN: 432 > MAX: 2622 > AVERAGE: 156217 > STDEV: 948,81 > VAR: 9,00E+05 > SUM: 9373 > > > Based on r.regression.line I get > > for map1=mapA and map2=mapB: > > a b R N F medX sdX medY sdY > 0.000458151 0.809242 0.99157 1021726 -0.98321 0.01077 > 5.3038 0.00917369 4.32854 > > and > > for map1=mapB and map2=mapB: > a b R N F medX sdX medY sdY > -0.000375823 1.21498 0.99157 1021726 -0.98321 0.00917369 > 4.32854 0.01077 5.3038 > > "R" is Pearson's correlation coefficient (as correctly > defined in the script "r.regression.line" in line 83 but > wrongly expressed as "sumXY - sumX*sumY/tot" in the > print-out in line 101). > > In openoffice-calc I get for these: > MapA MapB > 326 432 1,350792 Slope m > 641 850 0,138835 standard error of the slope > 1336 931 0,959458 RSQ (Square of "r") > 2020 1956 94,662802 4,000000 F value from the variance > analysis std error of regression for Y > 3197 2582 8213134,001379 sum of squared deviation of > estimated Y values from their linear mean > 3484 2622 > > or > > MapB MapB > 432 326 0,710293 Slope m > 850 641 0,073004 standard error of the slope > 931 1336 0,959458 RSQ > 1956 2020 94,662802 4,000000 F value from the variance > analysis std error of regression for Y > 2582 3197 4318750,949062 sum of squared deviation of > estimated Y values from their linear mean > 2622 3484 > > > (How is really r.regression.line functioning? Trying to > interpret the script is not that easy for me since I lack > of some basics in scripting) > > > Thank you, > > Nikos. > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > > -- View this message in context: http://www.nabble.com/Problems-with-v.external-tf4944319.html#a14167166 Sent from the Grass - Users mailing list archive at Nabble.com. _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
