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       i.class   -  Generates  spectral  signatures  for an image by allowing the user to outline
       regions of interest.
       The resulting signature file can be used as input for i.maxlik or as a seed signature file
       for i.cluster.


       imagery, classification


       i.class help
       i.class   map=name   group=name   subgroup=name  outsig=name   [insig=name]    [--verbose]

           Name of raster map to be displayed

           Name of input imagery group

           Name of input imagery subgroup

           File to contain result signatures

           File containing input signatures (seed)


       i.class performs the first pass in the  GRASS  two-pass  supervised  image  classification
       process;  the  GRASS program i.maxlik executes the second pass.  Both programs must be run
       to generate a classified map in GRASS raster format.

       i.class is an interactive program that allows the user to outline a region on  the  screen
       and  calculate  the  spectral  signature  based  on the cells that are within that region.
       During this process the user will be shown a histogram of the region for each image  band.
       The  user can also display the cells of the image bands which fall within a user-specified
       number of standard deviations from the means in the spectral signature.   By  doing  this,
       the  user can see how much of the image is likely to be put into the class associated with
       the current signature.

       The spectral signatures that result are composed of region means and covariance  matrices.
       These  region  means  and  covariance  matrices  are used in the second pass (i.maxlik) to
       classify the image.

       Alternatively, the spectral signatures generated by i.class can be used for seed means for
       the clusters in the i.cluster program.


       At  the command line the user is asked to enter the name of the raster map to be displayed
       during the process of outlining regions.  Typically, the user will want to enter the  name
       of  a  color composite previously created by r.composite.  However, the user can enter the
       name of any existing raster map.  This leaves the potential for using  a  raster  map  not
       directly derived from the image as a backdrop on which the user can outline the classes of

       The first screen in the program i.class asks the user for the imagery group  and  subgroup
       to be analyzed:
            Please select the group and subgroup to be analyzed
       GROUP:      spot_______   (list will show available groups)
       SUBGROUP:   123________   (list will show available subgroups)
                          (OR <Ctrl-C> TO CANCEL)

       The group should contain the imagery bands that the user wishes to classify.  The subgroup
       is a subset of this group.  The user must create a group and a  subgroup  by  running  the
       GRASS  program before running i.class.  The subgroup should contain only the image
       bands that the user wishes to classify.  Note that this subgroup must  contain  more  than
       one band.

       After  the first screen, the program asks the user for the name of the resulting signature
       file.  The signature file is both the output file for i.class and the required input  file
       for  the GRASS i.maxlik module.  It contains the region means and covariance matrices that
       are used to classify an image in  i.maxlik.  The signature  file  will  be  saved  in  the
       $MAPSET/group/$GROUP/subgroup/$SUBGROUP/sig/ directory.

       After entering the resulting signature file name, the user is asked to enter the name of a
       seed signature file.  This is optional.  A "seed" signature file is a  previously  created
       signature  file.   Such  a  seed  signature  file  may  be the result of an earlier run of
       i.class.  The seed signature file is copied into the new resulting signature  file  before
       any  new  signatures  are  added  by  i.class.  In this way, you can collect the work from
       several sessions with i.class into one signature file.

       At this point the i.class graphics screen will be drawn on the graphics  monitor  and  the
       user  will  be directed to use the mouse.  From this point on the user will primarily work
       with the mouse, selecting options from the menus and outlining regions on the screen.  The
       only time that the user will need to return to the text terminal is to enter names for the
       signatures created.


       The display frame layout that i.class uses is represented below for reference.
       |                       |                           |
       |                       |    Map Display Frame      |
       |                       |                           |
       |                       |                           |
       |   Histogram Display   |                           |
       |        Frame          |                           |
       |                       |                           |
       |                       |                           |
       |                       |                           |
       |                       +---------------------------+
       |                       |                           |
       |                       |    Zoom Display Frame     |
       |                       |                           |
       |                       |                           |
       |                       |                           |
       |                       |                           |
       |                       |                           |
       |                       |                           |
       |        Menu Frame                                 |


       All of the menus in the i.class program are displayed across the bottom  of  the  graphics
       monitor  in the Menu Frame.  To select an option from one of these menus, simply place the
       cursor over your selection and press any button on  the  mouse.   Each  of  the  menus  is
       discussed in the following paragraphs.

   The Command Menu
       The Command Menu includes the following selections:

              This  command  allows the user to outline a rectangular region in either the Map or
              Zoom Display Frames and the region is displayed, magnified,  to  fit  in  the  Zoom
              Display  Frame.  A red rectangle is drawn in the Map Display Frame, indicating what
              area the Zoom Display Frame shows.

       To outline the rectangular region simply use any mouse button to anchor the  first  corner
       of the border and then use any button to choose the other corner.

       Define region
              This  selection  takes the user to the Region Menu.  This menu includes the options
              that allow the user to outline a region of interest on the displayed raster map.

       Redisplay map
              This selection takes the user to the Redisplay Menu.  The Redisplay Menu allows the
              user to redraw map display frames.

       Analyze region
              This  selection  starts  the  process of analyzing the currently defined region.  A
              histogram of the defined region will be displayed for each band.  On the  histogram
              for  each  band,  the mean, standard deviation, minimum cell value and maximum cell
              value are marked.  The histograms are automatically scaled in an attempt to fit the
              data  into  the  space  available, but it is possible that all of the data will not
              fit.  In this case, as much of the data as possible, centered around the mean, will
              be  displayed.   After  the  histograms  are  displayed, the user will be given the
              Signature Menu.

              The user should make this selection to end the session with i.class.

   The Region Menu
       The Region Menu contains the following selections:

       Erase region
              This selection erases any currently defined region.

       Draw region
              This selection allows the user to use the mouse to draw a region on either the  Map
              or  Zoom  Display Frame.  An explanation of which mouse buttons to use is displayed
              in the Menu Frame.  The user does not need to try to complete the region  boundary.
              The last line of the region will be added when the user selects the Complete region
              option on the Region Menu.

       Restore last region
              This selection restores the  last  region  that  was  drawn.   After  a  region  is
              completed,  it  will  be  saved  to be restored later.  Only one previous region is

       Complete region
              This selection completes the region that is currently being drawn.  As noted above,
              it  saves  the  complete region to be restored later, if needed.  Once the user has
              made a complete region, it can be analyzed with the Analyze Region selection on the
              Command Menu.

              Use this selection to return to the Command Menu.

   The Redisplay Map Menu
       The Redisplay Map Menu has the following selections, which are useful to redraw the raster
       maps displayed in the Map and Zoom Display Frames.

       Map geographic region
              This selection causes the raster map in the Map Display Frame to be redrawn.

       Zoom region
              This selection causes the Zoom Display Frame to be redrawn.

              This selection causes both the Map and Zoom Display Frames to be redrawn.

              Use this selection if you do not want to redisplay either  of  the  above  regions.
              The user will be returned to the Command Menu.

   The Analyze Region Menu
       The  Analyze  Region  Menu  contains  the Signature Menu, which allows the user to set the
       number of standard deviations and the display color, and then to display (as  an  overlay)
       the  cells  that  match  the signature within the number of standard deviations specified.
       Note that once the matching cells are displayed, the Map Display Frame must be redisplayed
       to  see only the original raster map again.  The following selections are available on the
       Signature Menu:

       Set std dev's
              This selection allows the user to set the number of standard  deviations  from  the
              mean for the maximum and minimum range.  The maximum and minimum range is used when
              finding the cells that "match" the signature.  The user is presented with a menu of
              typical  choices  and  an "Other" option.  If the "Other" option is selected, enter
              the number  of  standard  deviations  from  the  keyboard  on  the  text  terminal.
              Otherwise,  the  selected  option  will  be  used.   When  the  number  of standard
              deviations is set, the histograms for each band will be redrawn  with  the  maximum
              and minimum range marked.

       Note  that  the  number in parentheses on this selection is the current number of standard

       Set color
              This selection allows the user to set the color  for  the  display  of  cells  that
              "match" the current signature.  The user is presented with a menu of color choices.
              The color selected will be used when the Display Matches Menu selection is made.

       Note that the color in parentheses on this selection is the current color for display.

       Display matches
              This selection displays the cells that "match" the current signature in the current
              color.   A  cell  "matches" the current signature if the cell value in each band is
              between the minimum range and maximum range for that band defined by the number  of
              standard deviations currently set.

              When  this  selection is chosen, the user will be asked whether or not he/she would
              like to save the current signature.  If the user answers with the "Yes"  selection,
              he/she will be asked to enter a description for the resultant signature file on the
              text terminal keyboard.  The saved signature  file  description  will  be  used  by
              i.maxlik  to  name  the category that is created from the current signature.  After
              either a "No" answer or the signature description is entered, the user is  returned
              to the Command Menu.


       i.class  uses  the  current MASK to generate the overlay for cells that match a signature.
       As a result, if a MASK already exists it will be removed  during  the  execution  of  this

       The  cell values in the image bands cannot fall outside of the range of 0 to 255.  i.class
       will report an error if they do.

       i.class, like some of the other imagery programs, does not use the standard GRASS  display
       frames.   After  running  i.class,  you  will  need to create a display frame (e.g., using
       d.frame or d.erase) before you can use most of the GRASS display (d.) commands. must be run before i.class to create an imagery group and  a  subgroup  containing
       the image bands to be classified.

       The  user  can  perform  a  supervised image classification by running i.class followed by
       i.maxlik.  The user can  perform  an  unsupervised  classification  by  running  i.cluster
       followed by i.maxlik.

       i.class is interactive and requires the user to be running a graphics display monitor (see
       d.mon) to run this program.


       The GRASS 4 Image Processing manual

       d.frame, d.mon, g.region, i.cca, i.cluster, r.composite,, i.maxlik, r.mapcalc


       David Satnik, Central Washington University

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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