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 [--verbose] [--quiet]
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:
63 i.vpoints
64 The first prompt in the program asks for the imagery group to be regis‐
66 tered . . .
67 Enter imagery group to be registered
68 Enter 'list' for a list of existing imagery groups
69 Enter 'list -f' for a verbose listing
70 Hit RETURN to cancel request
71 >
72 For example,
73 >list
74 might produce the following response:
76 <list>
77 Available groups
78 - - - - - - - - - - - - - - - - - - - - - - - - - -
79 test
80 - - - - - - - - - - - - - - - - - - - - - - - - - -
81 whereas,
82 >list -f
83 might produce the following response
85 Available groups
86 - - - - - - - - - - - - - - - - - - - - - - - - - -
87 test
88 photo in PERMANENT
89 res2 in tifftest
90 - - - - - - - - - - - - - - - - - - - - - - - - - -
91 The imagery group entered above should contain the files that you wish
92 to rectify. After entering the group to be registered, the terminal
93 screen displays the message:
94 >test
95 <test>
96 Use mouse now . . .
97 And the color graphics monitor displays the following screen:
98 Any single file in the imagery group may be used to mark points, and
100 points can be marked on more than one file in the imagery group to
101 accumulate the suggested minimum number of points (3 for a 1st order
102 transformation, 6 for a 2nd order, and 10 for a 3rd order). Any file
103 in the imagery group can be subsequently rectified (using i.rectify)
104 based on the transformation matrix computed from these points.
105 The chosen file is displayed in the upper left quadrant of the monitor
107 at a default magnification based on the extent of the current active
108 window.
109 RASTER IMAGE
111 The raster image option on the menu at the bottom of the window allows
113 the user to display any single file in the imagery group in the upper
114 right quadrant of the window screen. The option provides the same file
115 selection pick list as is presented when you first enter the i.vpoints
116 program. When you select this option, the program will erase the data
117 contained in all of the four quadrant windows and will reinitialize all
118 program values.
119 VECTOR MAPS
121 The vector maps option on the menu at the bottom of the screen allows
123 the user to display vector map data in the upper right quadrant of the
124 screen. After selecting the vector map layer to display, a menu selec‐
125 tion bar appears along the bottom on the screen. This pick list is used
126 to select the line color (blue, gray, green, red, white, or yellow) for
127 the selected vector data layer.
128 Refresh
130 The refresh option on the main menu allows the user to "refresh" or re-
132 draw the displayed vector data. This function will erase all outlines
133 showing the limits of previously zoomed areas. A "yes/no" roompt will
134 appear:
135 Refresh Map ? NO YES
136 Zoom
139 To enlarge a raster or vector image, place the mouse cross hairs on the
141 word zoom on the main menu and press the left button. The following
142 menu will be displayed at the bottom. of the screen:
143 CANCEL BOX POINT Select type of zoom
144 You have the option to identify the map extent of the zoom window
145 using either the mouse to define a box, or the mouse to mark a center
146 point from which to enlarge the image. The box option first prompts
147 you to identify a starting corner for the zoom region and then allows
148 you to define the area to be zoomed using a rubber band box. The
149 prompts appear as follows...
150 CANCEL Mark the first corner of region
151 CANCEL Define the region
152 After marking the first corner of the region to be enlarged, hold down
153 the left button and move the mouse to change the size and shape of the
154 rubber band box. After defining the area to be enlarged, press the
155 right button to accept it.
156 The point method for enlarging an image will display a mouse menu to
158 guide you in selecting the appropriate enlargement. To enlarge or
159 reduce the magnification factor, place the cursor on the "+" or "-" box
160 and press the left button on the mouse.
161 You may zoom either the raster or the vector display.
163 Upon accepting the new region limits, the raster or vector data are
165 redisplayed in either the lower left (raster) or lower right (vector)
166 windows.
167 The extent of the zoomed area is outlined on the unzoomed image in the
169 main window area.
170 While the main menu is displayed, you can mark corrosponding control
172 points on the raster and vector images or enter map coordinates from
173 the keyboard. If you are using coordinates taken from a reference map,
174 circle these points and then use whatever means you have available to
175 identify as precisely as possible the coordinate values for these
176 points. Digitizing software is recommended, especially GRASS v.digit.
177 Once you have determined the standard coordinates (for example, UTM's)
178 of each circled point, you are ready to mark the points on the dis‐
179 played image.
180 To mark the points on the image, that correspond to the points on the
182 standard coordinate map, place the mouse cross hairs on the point on
183 the image to be marked (you will probably have to ZOOM to find the
184 exact spot) and press the left hand button on the mouse. A diamond
185 shaped symbol will be marked on the image. The text monitor will dis‐
186 play the following screen:
187 Point 1 marked on the image at
188 East: 1023.77
189 North: -164.41
190 Enter coordinates as east north:
191 Analyze
192 After a number of points have been marked (a minimum of 4 for a 1st
194 order transformation, 7 for a 2nd order, and 11 for a 3rd order), the
195 RMS error of the points marked on the image can be checked. This is
196 done by placing the cross hairs on the word ANALYZE on the main menu at
197 the bottom of the monitor. The following error report is superimposed
198 on the monitor:
199 error image target
200 # col row target east north east north
201 1 -0.9 0.0 1.0 1048.5 -144.8 679132.5 4351080.6
203 2 1.0 0.4 1.3 2153.1 -567.2 684314.7 4399001.4
204 .
205 .
206 .
207 Overall rms error 76.85
208 The RMS error for the image being rectified is recorded under the col‐
209 umn "error" and subTITLEd "row' and "col". In the above report, the
210 marked point number 1 is 0.0 rows and -0.9 columns from the predicted
211 location calculated by the transformation equation. The RMS error for
212 the target database map is recorded under the heading "error" and the
213 subheading "target". This is the RMS error for the east and the north
214 coordinate values of the target map, but it is represented in the table
215 using one general value. The overall RMS error for the image is dis‐
216 played at the bottom of the screen in meters. Points that generate a
217 high RMS error are displayed in red on the monitor. The x,y coordinate
218 values of the point marked on the image being rectified are recorded
219 under the heading "image" and the subheadings "east" and "north". The
220 standard coordinate values of the point in the target database are
221 recorded under the heading "target" and the subheadings "east" and
222 "north". If the user would like to exclude or include a point, this
223 can be accomplished by placing the mouse cross hairs on the point num‐
224 ber to be included (if the point is absent) or excluded (if the point
225 is displayed) and then pressing the left button on the mouse twice.
226 When a point is excluded, it is not included in the calculation of the
227 RMS error, or included in the final transformation matrix. However, it
228 can be retrieved within i.vpoints at any time by double clicking with
229 the mouse as described above.
230 The following menu appears at the bottom of the monitor:
232 DONE PRINT FILE OVERLAY DELETE ON Transformation -
233 -> 1st ORDER Double click on point to be DELETED
234 Selecting DELETE ON will toggle the option to DELETE OFF, the toggle
235 option is used to allow the user to physically remove a control point
236 from the POINTS file instead of just flagging it as an non-active ref‐
237 erence point.
238 Overlay
240 Overlay allows the user to overlay the vector map(s) onto the raster
242 image. Overlay can be used to warp (register) and display the selected
243 vector map data on top of the raster image contained in the upper left
244 window of the color screen. An inverse coordinate transformation is
245 performed using the currently active order of transformation (i.e.,
246 first, second, or third).
247 Overlay vectors on raster image NO YES
248 By selecting the 1st ORDER option, the user may select the order of
249 transformation desired:
250 1st Order 2nd Order 3rd Order
251 The program will immediately recalculate the RMSE and the number of
252 points required.
253 Quit
255 To exit the i.vpoints program, place the mouse cross hairs on the word
257 QUIT at the bottom of the monitor and all of the marked points (includ‐
258 ing coordinates) will be saved.
259
261 The GRASS 4 Image Processing manual
262 g.mapsets
264 i.group
265 i.points
266 i.rectify
267 i.target
268
270 William R. Enslin, Michigan State University Center for Remote Sensing
271 Radim Blazek (update to GRASS 5.7)
272 Hamish Bowman (finish GRASS 6 porting)
273 Last changed: $Date: 2007-06-14 14:18:14 +0200 (Thu, 14 Jun 2007) $
275 Full index
277 © 2003-2008 GRASS Development Team
279GRASS 6.3.0 i.vpoints(1)