1i.class(1) Grass User's Manual i.class(1)
2
6 i.class - Generates spectral signatures for an image by allowing the
7 user to outline regions of interest.
8 The resulting signature file can be used as input for i.maxlik or as a
9 seed signature file for i.cluster.
10
12 imagery
13
15 i.class
16 i.class help
17 i.class map=name group=name subgroup=name outsig=name [insig=name]
18 [--verbose] [--quiet]
19 Parameters:
21 map=name
22 Name of raster map to be displayed
23 group=name
25 Name of input imagery group
26 subgroup=name
28 Name of input imagery subgroup
29 outsig=name
31 File to contain result signatures
32 insig=name
34 File containing input signatures (seed)
35
37 i.class performs the first pass in the GRASS two-pass supervised image
38 classification process; the GRASS program i.maxlik executes the second
39 pass. Both programs must be run to generate a classified map in GRASS
40 raster format.
41 i.class is an interactive program that allows the user to outline a
43 region on the screen and calculate the spectral signature based on the
44 cells that are within that region. During this process the user will
45 be shown a histogram of the region for each image band. The user can
46 also display the cells of the image bands which fall within a user-
47 specified number of standard deviations from the means in the spectral
48 signature. By doing this, the user can see how much of the image is
49 likely to be put into the class associated with the current signature.
50 The spectral signatures that result are composed of region means and
52 covariance matrices. These region means and covariance matrices are
53 used in the second pass (i.maxlik) to classify the image.
54 Alternatively, the spectral signatures generated by i.class can be used
56 for seed means for the clusters in the i.cluster program.
57
59 At the command line the user is asked to enter the name of the raster
60 map to be displayed during the process of outlining regions. Typi‐
61 cally, the user will want to enter the name of a color composite previ‐
62 ously created by r.composite. However, the user can enter the name of
63 any existing raster map. This leaves the potential for using a raster
64 map not directly derived from the image as a backdrop on which the user
65 can outline the classes of interest.
66 The first screen in the program i.class asks the user for the imagery
68 group and subgroup to be analyzed:
69 LOCATION: location SUPERVISED CLASSIFIER MAPSET: demo
70 Please select the group and subgroup to be analyzed
71 GROUP: spot_______ (list will show available groups)
72 SUBGROUP: 123________ (list will show available subgroups)
73 AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
74 (OR <Ctrl-C> TO CANCEL)
75 The group should contain the imagery bands that the user wishes to
78 classify. The subgroup is a subset of this group. The user must cre‐
79 ate a group and a subgroup by running the GRASS program i.group before
80 running i.class. The subgroup should contain only the image bands that
81 the user wishes to classify. Note that this subgroup must contain more
82 than one band.
83 After the first screen, the program asks the user for the name of the
85 resulting signature file. The signature file is both the output file
86 for i.class and the required input file for the GRASS program i.maxlik.
87 It contains the region means and covariance matrices that are used to
88 classify an image in i.maxlik.
89 After entering the resulting signature file name, the user is asked to
91 enter the name of a seed signature file. This is optional. A "seed"
92 signature file is a previously created signature file. Such a seed
93 signature file may be the result of an earlier run of i.class. The
94 seed signature file is copied into the new resulting signature file
95 before any new signatures are added by i.class. In this way, you can
96 collect the work from several sessions with i.class into one signature
97 file.
98 At this point the i.class graphics screen will be drawn on the graphics
100 monitor and the user will be directed to use the mouse. From this
101 point on the user will primarily work with the mouse, selecting options
102 from the menus and outlining regions on the screen. The only time that
103 the user will need to return to the text terminal is to enter names for
104 the signatures created.
105
107 The display frame layout that i.class uses is represented below for
108 reference.
109 +-----------------------+---------------------------+
110 | | |
111 | | Map Display Frame |
112 | | |
113 | | |
114 | Histogram Display | |
115 | Frame | |
116 | | |
117 | | |
118 | | |
119 | +---------------------------+
120 | | |
121 | | Zoom Display Frame |
122 | | |
123 | | |
124 | | |
125 | | |
126 | | |
127 | | |
128 +-----------------------+---------------------------+
129 | Menu Frame |
130 +---------------------------------------------------+
131
134 All of the menus in the i.class program are displayed across the bottom
135 of the graphics monitor in the Menu Frame. To select an option from
136 one of these menus, simply place the cursor over your selection and
137 press any button on the mouse. Each of the menus is discussed in the
138 following paragraphs.
139 The Command Menu
141 The Command Menu includes the following selections:
142 Zoom
144 This command allows the user to outline a rectangular region in
145 either the Map or Zoom Display Frames and the region is dis‐
146 played, magnified, to fit in the Zoom Display Frame. A red rec‐
147 tangle is drawn in the Map Display Frame, indicating what area
148 the Zoom Display Frame shows.
149 To outline the rectangular region simply use any mouse button to anchor
151 the first corner of the border and then use any button to choose the
152 other corner.
153 Define region
155 This selection takes the user to the Region Menu. This menu
156 includes the options that allow the user to outline a region of
157 interest on the displayed raster map.
158 Redisplay map
160 This selection takes the user to the Redisplay Menu. The Redis‐
161 play Menu allows the user to redraw map display frames.
162 Analyze region
164 This selection starts the process of analyzing the currently
165 defined region. A histogram of the defined region will be dis‐
166 played for each band. On the histogram for each band, the mean,
167 standard deviation, minimum cell value and maximum cell value
168 are marked. The histograms are automatically scaled in an
169 attempt to fit the data into the space available, but it is pos‐
170 sible that all of the data will not fit. In this case, as much
171 of the data as possible, centered around the mean, will be dis‐
172 played. After the histograms are displayed, the user will be
173 given the Signature Menu.
174 Quit
176 The user should make this selection to end the session with
177 i.class.
178 The Region Menu
180 The Region Menu contains the following selections:
181 Erase region
183 This selection erases any currently defined region.
184 Draw region
186 This selection allows the user to use the mouse to draw a region
187 on either the Map or Zoom Display Frame. An explanation of
188 which mouse buttons to use is displayed in the Menu Frame. The
189 user does not need to try to complete the region boundary. The
190 last line of the region will be added when the user selects the
191 Complete region option on the Region Menu.
192 Restore last region
194 This selection restores the last region that was drawn. After a
195 region is completed, it will be saved to be restored later.
196 Only one previous region is saved.
197 Complete region
199 This selection completes the region that is currently being
200 drawn. As noted above, it saves the complete region to be
201 restored later, if needed. Once the user has made a complete
202 region, it can be analyzed with the Analyze Region selection on
203 the Command Menu.
204 Done
206 Use this selection to return to the Command Menu.
207 The Redisplay Map Menu
209 The Redisplay Map Menu has the following selections, which are useful
210 to redraw the raster maps displayed in the Map and Zoom Display Frames.
211 Map geographic region
213 This selection causes the raster map in the Map Display Frame to
214 be redrawn.
215 Zoom region
217 This selection causes the Zoom Display Frame to be redrawn.
218 Both
220 This selection causes both the Map and Zoom Display Frames to be
221 redrawn.
222 Cancel
224 Use this selection if you do not want to redisplay either of the
225 above regions. The user will be returned to the Command Menu.
226 The Analyze Region Menu
228 The Analyze Region Menu contains the Signature Menu, which allows the
229 user to set the number of standard deviations and the display color,
230 and then to display (as an overlay) the cells that match the signature
231 within the number of standard deviations specified. Note that once the
232 matching cells are displayed, the Map Display Frame must be redisplayed
233 to see only the original raster map again. The following selections
234 are available on the Signature Menu:
235 Set std dev's
237 This selection allows the user to set the number of standard
238 deviations from the mean for the maximum and minimum range. The
239 maximum and minimum range is used when finding the cells that
240 "match" the signature. The user is presented with a menu of
241 typical choices and an "Other" option. If the "Other" option is
242 selected, enter the number of standard deviations from the key‐
243 board on the text terminal. Otherwise, the selected option will
244 be used. When the number of standard deviations is set, the
245 histograms for each band will be redrawn with the maximum and
246 minimum range marked.
247 Note that the number in parentheses on this selection is the current
249 number of standard deviations.
250 Set color
252 This selection allows the user to set the color for the display
253 of cells that "match" the current signature. The user is pre‐
254 sented with a menu of color choices. The color selected will be
255 used when the Display Matches Menu selection is made.
256 Note that the color in parentheses on this selection is the current
258 color for display.
259 Display matches
261 This selection displays the cells that "match" the current sig‐
262 nature in the current color. A cell "matches" the current sig‐
263 nature if the cell value in each band is between the minimum
264 range and maximum range for that band defined by the number of
265 standard deviations currently set.
266 Done
268 When this selection is chosen, the user will be asked whether or
269 not he/she would like to save the current signature. If the
270 user answers with the "Yes" selection, he/she will be asked to
271 enter a description for the resultant signature file on the text
272 terminal keyboard. The saved signature file description will be
273 used by i.maxlik to name the category that is created from the
274 current signature. After either a "No" answer or the signature
275 description is entered, the user is returned to the Command
276 Menu.
277
279 i.class uses the current MASK to generate the overlay for cells that
280 match a signature. As a result, if a MASK already exists it will be
281 removed during the execution of this program.
282 The cell values in the image bands cannot fall outside of the range of
284 0 to 255. i.class will report an error if they do.
285 i.class, like some of the other imagery programs, does not use the
287 standard GRASS display frames. After running i.class, you will need to
288 create a display frame (e.g., using d.frame or d.erase) before you can
289 use most of the GRASS display (d.) commands.
290 i.group must be run before i.class to create an imagery group and a
292 subgroup containing the image bands to be classified.
293 The user can perform a supervised image classification by running
295 i.class followed by i.maxlik. The user can perform an unsupervised
296 classification by running i.cluster followed by i.maxlik.
297 i.class is interactive and requires the user to be running a graphics
299 display monitor (see d.mon) to run this program.
300
302 The GRASS 4 Image Processing manual
303 d.frame, d.mon, g.region, i.cca, i.cluster, r.composite, i.group,
305 i.maxlik, r.mapcalc
306
308 David Satnik, Central Washington University
309 Last changed: $Date: 2007-06-14 14:18:14 +0200 (Thu, 14 Jun 2007) $
311 Full index
313 © 2003-2008 GRASS Development Team
315GRASS 6.3.0 i.class(1)