This is a question for those of you with experience in classification and feature extraction from multiband imagery.
I've been using MultiSpec (a program I can highly recommend, that is also public domain) and a couple other pieces of software, but want to start using GRASS for at least some work. So, I want to do some comparisons of GRASS's supervised and unsupervised classification routines with those of other programs I use.
I have a 14-band ASTER image I've imported into GRASS and want to start with an unsupervised classification in a search for a particular set of prehistoric earthworks.
I set up the required groups and subgroups. Then I ran i.clust and it appeared to work fine. I started with 25 classes, as I am looking for some rather fine-scale features, and left the rest of the defaults alone for now. The output text said it ran the appropriate iterations. I had it save a text report and this looked OK. The signature file *looks* OK also and was placed by GRASS in the /group/[name]/subgroup/[name]/sig folder.
I then tried i.maxlik. It produced an output to screen of 25 lines that said
"WARNING: signature 1 is not valid (ill-conditioned) - ignored"
and so forth for signatures 1-25, followed by
i.maxlik ... 0%
It produced no classification map obviously.
I also tried the the i.smap classification routine using the same signature file. It also produced an error:
"WARNING: unable to open signature file AST_1336_clustsig for subgroup nonthermal_bands of group [AST.1336 in satellite].
ERROR: signature file [AST_1336_clustsig] missing or unreadable."
I haven't misspelled anything. I also output my GRASS data (same region window and everything) to a *.lan file and read it into Multispec. I had no trouble doing an unsupervised classification and (happily) it produced potentially interesting results without even futzing with the default values.
Any suggestions?
______________________________
Michael Barton, Professor & Curator
Department of Anthropology
Arizona State University
Tempe, AZ 85287-2402
USA
voice: 480-965-6262; fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton