Multiple regions/signature in i.class

[Michael Shapiro]

I assume you mean that you would like i.class  to  allow  you  to
define  2  or  more  polygons that form a single class instead of
assuming that each polygon is a unique class. It  can't  be  done
with i.class now.

You could get around this  by  using  r.reclass  to  combine  the
classes i.class forced you to separate. This may result in a good
classification and it may not. If the spectral variance would  be
large  if  both  classes  were  combined before classifiying, the
results wouldn't be good. But with the  was  i.class  works  now,
reclassifying after classification kmight give good results.


There will be a new program (i.gensig) that will  allow  multiple
regions  to  be  considered  as  the same class and have a common
signature. It will be part of 4.1  However  it  is  not  part  of
i.class.  You  will  have  to construct the "training polgons" by
digitizing them using an image as  the  backdrop.  i.gensig  will
take this training map and construct signatures for the class you
have defined. You would used either v.digit or r.digit (to be part of
4.1) to create the training map. However, you will not get the
feedback i.class gives you to know if you have constructed "reasonable"
signatures as you create the trainging map. i.gensig was designed to
generate signatures for maps that were ground truthed in part of
the study area.

|
|I have been experimenting with i.class to perform a supervised
|classification of a SPOT image.  Could someone please tell me if
|it is possible to define multiple regions for a single
|information class (or signature)?  I would like to identify
|agricultural fields planted in particular crops and some of these
|are relatively small.  Therefore, I would like to build a signature
|around several training sites in order to increase my
|sample of DNs for each class.  Thanks in advance!
|
|


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Michael Shapiro                        U.S. Army CERL                  
email:   shapiro at amber.cecer.army.mil  Office of GRASS Integration
phone:   (217) 373-7277                P.O. Box 9005                   
fax:     (217) 373-7222                Champaign, Ill. 61826-9005
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