Hamish wrote: > I am working with MODIS Aqua imagery in HDF4 format. (level 3) > http://oceancolor.gsfc.nasa.gov/PRODUCTS/ > > The Chlorophyll-a concentration data comes in log form, 0-65535. > Plotting the data with a bcyr color rules makes it look great. > > I added a mini-tutorial here: > http://grass.gdf-hannover.de/wiki/MODIS > > > The metadata (available through gdalinfo) gives the formula and test > points to convert to mg/m^3: > r.mapcalc "${map}.chlor_a = 10^(($Slope * $map) + $Intercept)"
> ie a histogram of that starts high and exponentially drops to 0. By 2.0 > there are few data cells left, but real data continues up to the max in > areas having plankton blooms. > > > So how to make nice color rules for that? 'r.colors -g' does the opposite > of what I want, Odd. Theoretically, it should do exactly what you want. > 'r.colors -e' shows some more detail but isn't really > right. A custom one using 'r.univar precentile=,,,,' cues shows some more > but isn't smooth and is a pain. > > > Any ideas? Could G_log_colors() be turned on its head to make a > G_exp_colors() function and associated 'r.colors -x' flag? Would it work? It could be done easily enough, although I'm not sure how useful it would be. -- Glynn Clements <[EMAIL PROTECTED]> _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev