Even wrote: > #correct azimuth to East (GRASS convention): > # this seems to be backwards, but in fact it works so > leave it. > az = float(azimuth) - 90
I'm not into checking-in fudge factors which I don't understand, and I seem to recall that when I wrote that comment I did actually investigate the r.mapcalc algorithm and determine that it was "in fact" doing the right thing, or at least verified the output was correct. GRASS has, for decades, used the mathematical convention of theta measured CCW from the positive x-axis for measuring aspect, not the nautical convention of of degrees measured CW from north. Both ways are neither right nor wrong, it's just the convention used. (a reminder that grass's roots are in modeling and mathematical analysis, not cartography) The typical way to convert between the two conventions is: naut = 90 - theta theta = 90 - naut There is the possiblity that when gdal copied this code from GRASS they only got/rewrote half of it, or lost the matching color table, etc. ?? If you like add it as a wish in the grass trac'er assigned to me, I could dig into it at some time in the future. sorry I don't have much time at all right now to look into itfurther. Only to say that I have looked into this in the past and signed off on it as ok back then (for use within GRASS, no idea about gdal's implimentation). hope that helps a little, Hamish _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
