1i.vpoints(1) Grass User's Manual i.vpoints(1)
2
6 i.vpoints - Set registration points for an imagery group from a vector
7 map or keyboard entry.
8
10 imagery
11
13 i.vpoints
14 i.vpoints help
15 i.vpoints group=string
16 Parameters:
18 group=string
19 Name of imagery group to be registered
20
22 This program enables the user to identify coordinate pairs of points
23 from a vector map or keyboard entry and corresponding points in an
24 image to be rectified. The map coordinate values of each point are used
25 to calculate a transformation matrix. The operator may then use the
26 i.rectify program to rectify the image using the transformation matrix
27 coefficients calculated from the control point file created in
28 i.vpoints. The
29 i.rectify program performs a first, second or third order transforma‐
30 tion of the image.
31 The first step is to display the unrectified image and corresponding
33 vector map data. The operator would then mark corresponding control
34 point locations on the image and map. To identify the precise location
35 of a point to be marked, i.vpoints has a zoom option. In addition to
36 marking control points on an image to be rectified and inputting their
37 world coordinate values using the keyboard, i.vpoints has the option
38 to simultaneously display vector map data available in the targeted
39 database, and identify on the vector map the location of the corre‐
40 sponding marked points. When this option is chosen, the coordinate
41 values are input automatically. Any GRASS map layer or vector map in
42 the targeted database LOCATION can be displayed using i.vpoints. The
43 i.vpoints program also has the capability of overlaying (i.e., warping)
44 the vector data onto the raster image to visually check the accuracy of
45 the registration based on the current set of active control points.
46 During the process of marking points and entering map coordinates, the
47 user can compute the RMS (root mean square) error for each point
48 entered. The i.vpoints program does this by calculating a transforma‐
49 tion equation (the same one that is calculated in the GRASS program
50 i.rectify 2). Coefficients are computed for the equation. The coeffi‐
51 cients are then used in the equation along with the x,y coordinates of
52 the marked points. The results are plugged into an equation for RMS
53 error. The interpretation of RMS error is described in the ANALYZE
54 subsection.
55 The procedures for marking control points (registration points), dis‐
57 playing vector map layers, overlaying vector maps onto the raster
58 image, and calculating RMS error are described in the following sec‐
59 tions .
60 To enter the program (the i.vpoints program requires the use of a
62 graphics monitor) type i.vpoints: i.vpoints
63 The first prompt in the program asks for the imagery group to be regis‐
65 tered . . .
66 Enter imagery group to be registered
67 Enter 'list' for a list of existing imagery groups
68 Enter 'list -f' for a verbose listing
69 Hit RETURN to cancel request
70 >
71 For example, >list
72 might produce the following response:
74 <list>
75 Available groups
76 - - - - - - - - - - - - - - - - - - - - - - - - - -
77 test
78 - - - - - - - - - - - - - - - - - - - - - - - - - -
79 whereas, >list -f
80 might produce the following response
82 Available groups
83 - - - - - - - - - - - - - - - - - - - - - - - - - -
84 test
85 photo in PERMANENT
86 res2 in tifftest
87 - - - - - - - - - - - - - - - - - - - - - - - - - -
88 The imagery group entered above should contain the files that you wish
89 to rectify. After entering the group to be registered, the terminal
90 screen displays the message:
91 >test
92 <test>
93 Use mouse now . . .
94 And the color graphics monitor displays the following screen:
95 Any single file in the imagery group may be used to mark points, and
97 points can be marked on more than one file in the imagery group to
98 accumulate the suggested minimum number of points (3 for a 1st order
99 transformation, 6 for a 2nd order, and 10 for a 3rd order). Any file
100 in the imagery group can be subsequently rectified (using i.rectify)
101 based on the transformation matrix computed from these points.
102 The chosen file is displayed in the upper left quadrant of the monitor
104 at a default magnification based on the extent of the current active
105 window.
106 RASTER IMAGE
108 The raster image option on the menu at the bottom of the window allows
110 the user to display any single file in the imagery group in the upper
111 right quadrant of the window screen. The option provides the same file
112 selection pick list as is presented when you first enter the i.vpoints
113 program. When you select this option, the program will erase the data
114 contained in all of the four quadrant windows and will reinitialize all
115 program values.
116 VECTOR MAPS
118 The vector maps option on the menu at the bottom of the screen allows
120 the user to display vector map data in the upper right quadrant of the
121 screen. After selecting the vector map layer to display, a menu selec‐
122 tion bar appears along the bottom on the screen. This pick list is used
123 to select the line color (blue, gray, green, red, white, or yellow) for
124 the selected vector data layer.
125 Refresh
127 The refresh option on the main menu allows the user to "refresh" or re-
129 draw the displayed vector data. This function will erase all outlines
130 showing the limits of previously zoomed areas. A "yes/no" roompt will
131 appear:
132 Refresh Map ? NO YES
133 Zoom
136 To enlarge a raster or vector image, place the mouse cross hairs on the
138 word zoom on the main menu and press the left button. The following
139 menu will be displayed at the bottom. of the screen:
140 CANCEL BOX POINT Select type of zoom
141 You have the option to identify the map extent of the zoom window
142 using either the mouse to define a box, or the mouse to mark a center
143 point from which to enlarge the image. The box option first prompts
144 you to identify a starting corner for the zoom region and then allows
145 you to define the area to be zoomed using a rubber band box. The
146 prompts appear as follows...
147 CANCEL Mark the first corner of region
148 CANCEL Define the region
149 After marking the first corner of the region to be enlarged, hold down
150 the left button and move the mouse to change the size and shape of the
151 rubber band box. After defining the area to be enlarged, press the
152 right button to accept it.
153 The point method for enlarging an image will display a mouse menu to
155 guide you in selecting the appropriate enlargement. To enlarge or
156 reduce the magnification factor, place the cursor on the "+" or "-" box
157 and press the left button on the mouse.
158 You may zoom either the raster or the vector display.
160 Upon accepting the new region limits, the raster or vector data are
162 redisplayed in either the lower left (raster) or lower right (vector)
163 windows.
164 The extent of the zoomed area is outlined on the unzoomed image in the
166 main window area.
167 While the main menu is displayed, you can mark corrosponding control
169 points on the raster and vector images or enter map coordinates from
170 the keyboard. If you are using coordinates taken from a reference map,
171 circle these points and then use whatever means you have available to
172 identify as precisely as possible the coordinate values for these
173 points. Digitizing software is recommended, especially GRASS v.digit.
174 Once you have determined the standard coordinates (for example, UTM's)
175 of each circled point, you are ready to mark the points on the dis‐
176 played image.
177 To mark the points on the image, that correspond to the points on the
179 standard coordinate map, place the mouse cross hairs on the point on
180 the image to be marked (you will probably have to ZOOM to find the
181 exact spot) and press the left hand button on the mouse. A diamond
182 shaped symbol will be marked on the image. The text monitor will dis‐
183 play the following screen:
184 Point 1 marked on the image at
185 East: 1023.77
186 North: -164.41
187 Enter coordinates as east north:
188 Analyze
189 After a number of points have been marked (a minimum of 4 for a 1st
191 order transformation, 7 for a 2nd order, and 11 for a 3rd order), the
192 RMS error of the points marked on the image can be checked. This is
193 done by placing the cross hairs on the word ANALYZE on the main menu at
194 the bottom of the monitor. The following error report is superimposed
195 on the monitor:
196 error image target
197 # col row target east north east north
198 1 -0.9 0.0 1.0 1048.5 -144.8 679132.5 4351080.6
200 2 1.0 0.4 1.3 2153.1 -567.2 684314.7 4399001.4
201 .
202 .
203 .
204 Overall rms error 76.85
205 The RMS error for the image being rectified is recorded under the col‐
206 umn "error" and subTITLEd "row' and "col". In the above report, the
207 marked point number 1 is 0.0 rows and -0.9 columns from the predicted
208 location calculated by the transformation equation. The RMS error for
209 the target database map is recorded under the heading "error" and the
210 subheading "target". This is the RMS error for the east and the north
211 coordinate values of the target map, but it is represented in the table
212 using one general value. The overall RMS error for the image is dis‐
213 played at the bottom of the screen in meters. Points that generate a
214 high RMS error are displayed in red on the monitor. The x,y coordinate
215 values of the point marked on the image being rectified are recorded
216 under the heading "image" and the subheadings "east" and "north". The
217 standard coordinate values of the point in the target database are
218 recorded under the heading "target" and the subheadings "east" and
219 "north". If the user would like to exclude or include a point, this
220 can be accomplished by placing the mouse cross hairs on the point num‐
221 ber to be included (if the point is absent) or excluded (if the point
222 is displayed) and then pressing the left button on the mouse twice.
223 When a point is excluded, it is not included in the calculation of the
224 RMS error, or included in the final transformation matrix. However, it
225 can be retrieved within i.vpoints at any time by double clicking with
226 the mouse as described above.
227 The following menu appears at the bottom of the monitor:
229 DONE PRINT FILE OVERLAY DELETE ON Transformation -
230 -> 1st ORDER Double click on point to be DELETED
231 Selecting DELETE ON will toggle the option to DELETE OFF, the toggle
232 option is used to allow the user to physically remove a control point
233 from the POINTS file instead of just flagging it as an non-active ref‐
234 erence point.
235 Overlay
237 Overlay allows the user to overlay the vector map(s) onto the raster
239 image. Overlay can be used to warp (register) and display the selected
240 vector file data on top of the raster image contained in the upper left
241 window of the color screen. An inverse coordinate transformation is
242 performed using the currently active order of transformation (i.e.,
243 first, second, or third).
244 Overlay vectors on raster image NO YES
245 By selecting the 1st ORDER option, the user may select the order of
246 transformation desired:
247 1st Order 2nd Order 3rd Order
248 The program will immediately recalculate the RMSE and the number of
249 points required.
250 Quit
252 To exit the i.vpoints program, place the mouse cross hairs on the word
254 QUIT at the bottom of the monitor and all of the marked points (includ‐
255 ing coordinates) will be saved.
256
258 GRASS Tutorial: Image Processing
259 g.mapsets
261 i.group
262 i.points
263 i.rectify
264 i.target
265
267 William R. Enslin, Michigan State University Center for Remote Sensing
268 Radim Blazek (update to GRASS 5.7)
269 Hamish Bowman (finish GRASS 6 porting)
270 Last changed: $Date: 2006/06/28 15:52:42 $
272 Full index
274GRASS 6.2.2 i.vpoints(1)