On Thu, Jul 4, 2013 at 11:13 AM, Moritz Lennert <mlenn...@club.worldonline.be> wrote: > As you might have gathered from my other messages on the list, we are > currently running tests of i.segment in our department. A few questions came > up (with my attempts at answers). > > > *************************** >> >> I had a look at the results, they are interesting. Maybe you could also >> try >> a combination of panchromatic, red and near-infrared bands and leave the >> other bands out. If it is possible to give different weights to the bands, >> then maybe 2 for the pan, 1 for red and 1 for NIR. > > > I think that is possible, but I have to check how. I imagine you would > work at the resolution of the pan for this...
You could first resample the pan band to the resolution of the other bands, then r.mapcalc - multiply the pan band with 2 and use i.segment -w. > >> >> Regarding the size of the segments, we generally combine different >> segmentations, fine and coarse, depending on the type of objects that we >> have to classify. We also combine different segmentations because then we >> can use the classification of a fine segmentation as attribute for >> classifying a coarse segmentation (e.g. counting trees or houses in a >> large >> segment). Here we have very small segments and also very large ones >> together >> in the results, it is a bit different. > > > So to be able to do what you do now, you would need homogenous segment > sizes, i.e. not only a minsize (which I set fairly low in this first > trial: 2 pixels), but also the equivalent of a maxsize. Then, if you set the > two fairly close to each other (i.e. minsize=900 and maxsize=1100 to get > segments of +/- 1000 pixels). This is currently controlled with the threshold value. I am not sure if a max size makes sense. There might be homogenous objects with identical pixel values (difference = 0) that are larger than a given max size. Splitting such objects to respect a max size would be arbitrary. I would rather try to find a good combination of threshold and minsize, and do hierachical segmentation using the output of the previous run as input for the next run with increasing threshold. Technically, a maxsize option is possible for i.segment. Markus M > > I'll see how that can be achieved with the currently implemented module. > ******************************* > > Any hints on possible answers to these issues ? > > Moritz _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev