1photo.2target(1) Grass User's Manual photo.2target(1)
2
6 photo.2target - Creates control points on an image to be ortho-recti‐
7 fied.
8
10 imagery
11
13 photo.2target
14 photo.2target help
15 photo.2target group=string [map=name] [target=name] [--verbose]
16 [--quiet]
17 Parameters:
19 group=string
20 Name of imagery group
21 map=name
23 Name of image to be rectified which will be initialy drawn on
24 screen.
25 target=name
27 Name of a map from target mapset which will be initialy drawn on
28 screen.
29
31 photo.2target is an imagery function that enables you to mark control
32 points on an image to be ortho-rectified and then input the coordinates
33 of each point for calculation of rectification parameters. Rectifica‐
34 tion is the mapping of an image from one coordinate system to another.
35 The geometry of an image extracted into a GRASS LOCATION having an x,y
36 coordinate system is not planimetric. To create a planimetric image,
37 that is, to convert the x,y coordinate system into a standard coordi‐
38 nate system (for example, the UTM coordinate system or the State Plane
39 coordinate system), points from a map having the standard coordinates
40 must be associated with the same points on the image to be rectified.
41 The ortho-rectification parameters are computed in two phases. The
42 first phase computes a transformation matrix between image (row,col)
43 coordinates and photo (x,y) coordinates relative to the perspective
44 center. The transformation matrix is computed explicitly in the option
45 photo.2image . The second phase, photo.2target, enables you to mark
46 control points on the image and then input the standard coordinates
47 (Easting,Northing, and elevation) to determine the parameters for a
48 three dimensional projective transformation. photo.init
49 may be run before running photo.2target to modify the initial camera
50 exposure station parameters, and/or modify the standard deviation of
51 these parameters. photo.init
52 is not required but generally is helpful.
53 During the process of marking control points and entering standard
55 coordinates, you may compute the RMS (root mean square) error for each
56 control point entered. photo.2target does this by calculating the
57 transformation equation, and then plugging these results into an equa‐
58 tion for RMS error.
59 photo.2target offers a zoom option to locate precisely the point to be
61 marked on an image. This program also offers you the option of acquir‐
62 ing standard coordinates for a marked point from a map layer in the
63 target database, or from a digitizer.
64 To run photo.2target, a graphics monitor is required.
66 The procedure for marking points, entering coordinates, and calculating
68 RMS error is described below.
69 The terminal screen displays the following message:
71 use mouse now...
73 The graphics monitor displays the following screen:
75 +-----------------------------+--------------------------------+
78 |imagery filename (mag) | target filename (mag) |
79 +-----------------------------+--------------------------------+
80 | | |
81 | | |
82 | | |
83 | | |
84 | | |
85 | | |
86 | | |
87 +-----------------------------+--------------------------------+
88 | | |
89 | | |
90 | | |
91 | | |
92 | | |
93 | | |
94 +-----------------------------+--------------------------------+
95 |QUIT ZOOM PLOTCELL ANALYZE | |
96 +-----------------------------+--------------------------------+
97 A pop-down menu like that shown below will be superimposed on the left
100 half of the screen:
101 +------------------------------------------+
104 | Double click on raster map to be plotted |
105 | Double click here to cancel |
106 +------------------------------------------+
107 +--------------------+
108 | Mapset PERMANENT |
109 +---------+----------+
110 |gs13.1 | gs14.1 |
111 +---------+----------+
112 |gs21.1 | gs22.2 |
113 +---------+----------+
114 Any single file in the imagery group may be used to mark points, and
117 you can mark points on more than one file in the imagery group to accu‐
118 mulate the 12 points suggested minimum. Any file in the imagery group
119 can be rectified (using photo.rectify ) based on the rectification
120 parameters computed from these control points.
121 The imagery file you select is displayed in the upper left quadrant of
123 the screen.
124
126 To magnify the displayed file, you must place the mouse cross hairs on
127 the word ZOOM. The following menu will then be displayed at the bottom
128 of the screen:
129 +-------+-----+-------++--------------------+
132 |Cancel | Box | Point ||Select type of ZOOM |
133 +-------+-----+-------++--------------------+
134 You may identifying the zoom window either by using the mouse to make a
137 box, or by using the mouse to mark the center of the window and enter‐
138 ing a magnification factor. The terminal screen will display a mouse
139 button menu to guide you in identifying the window.
140 It is also possible to start zoom by box with middle mouse button and
142 pan by right mouse button.
143
145 To mark the points on the image that correspond to the points on a
146 standard coordinate system map, you must place the mouse cross hairs on
147 the corresponding location on the image to be marked and press the left
148 hand button on the mouse. A diamond shaped symbol will be marked on
149 the image. The terminal will display the following menu:
150 +------------------------------------+--------------------------+
153 |Point 1 marked at IMAGE COORDINATES | |
154 |IMAGE X: 1023.77 | |
155 |IMAGE Y: -164.41 | |
156 | | |
157 +------------------------------------+--------------------------+
158 |Enter CONTROL COORDINATES as east,north,elevation: |
159 +---------------------------------------------------------------+
160 You then enter the easting, northing, and elevation for the point
163 marked on the image. If you wish not to enter a coordinate, simply hit
164 RETURN to return control to the mouse; the marked point then disap‐
165 pears.
166 Entered point can be canceled by right mouse button click.
168
170 In addition to acquiring control points from a standard map, you have
171 the option of acquiring the points from a cell-map in the target data‐
172 base. The database map is displayed by placing the mouse cross hairs
173 on the words PLOT CELL. The following line is then displayed at the
174 bottom of the monitor:
175 +-------+---------------------------------------+
178 |Cancel | Indicate which side should be plotted |
179 +-------+---------------------------------------+
180 Which side of the monitor is to be plotted is indicated by placing the
183 mouse cross hairs on the half of the monitor screen that you would like
184 to use, and pressing the left mouse button. The following pop-down
185 menu will be superimposed on the half of the screen that was chosen:
186 +------------------------------------------+
189 | Double click on raster map to be plotted |
190 | Double click here to cancel |
191 +------------------------------------------+
192 +-----------------------------+
194 | Mapset user1 |
195 +--------------+--------------+
196 |tm.rectified | |
197 +--------------+--------------+
198 |tm.classified | |
199 +--------------+--------------+
200 | Mapset PERMANENT |
201 +--------------+--------------+
202 |elevation | geology |
203 +--------------+--------------+
204 |slope | soils |
205 +--------------+--------------+
206 |aspect | |
207 +--------------+--------------+
208 |roads | |
209 +--------------+--------------+
210 |streams | |
211 +--------------+--------------+
212 |airfields | |
213 +--------------+--------------+
214 After the map is displayed the following message appears at the bottom
217 of the monitor:
218 +-----------------+----------+--------+
221 |input method -> | keyboard | screen |
222 +-----------------+----------+--------+
223 If you wish to use the plotted map only as a comparative reference, the
226 keyboard can be chosen as the means to input coordinates corresponding
227 to the marked control points. This is done by placing the mouse cross
228 hairs on the word KEYBOARD and pressing the left button on the mouse.
229 If you select the SCREEN option, points marked on the image will auto‐
231 matically be associated with the coordinates from the corresponding
232 points on the target database map, and a corresponding elevation from
233 the cell-file selected for elevation data. In this option, when you
234 mark a point on the image, the following menu is displayed on the ter‐
235 minal:
236 +------------------------------------+--------------------------+
239 |Point 5 marked at IMAGE COORDINATES | |
240 |IMAGE X: 1023.77 | |
241 |IMAGE Y: -164.41 | |
242 | | |
243 | | |
244 |Control Point location | |
245 |East: 679132.57 | |
246 |North: 4351080.67 | |
247 |Elevation: 1010.00 | |
248 | | |
249 | | |
250 | | |
251 +------------------------------------+--------------------------+
252 |use mouse now... |
253 +---------------------------------------------------------------+
254 The coordinates for the target database map are automatically saved as
257 the coordinates corresponding to the marked control point on the image.
258
260 After a number of points have been marked (4 to 7), you can check the
261 RMS error of the points marked on the image. This is done by placing
262 the mouse cross hairs on the word ANALYZE at the bottom of the monitor.
263 An error report resembling that shown below is superimposed on the mon‐
264 itor:
265 +--------------------------------------------------------------------------+
268 | error
269 |
270 |# east north target east north east north elev.
271 |
272 +--------------------------------------------------------------------------+
273 |1 0.0 -0.9 1.0 48.5 4.8 79132.5 351080.6 10.0
274 |
275 |2 0.4 1.0 1.3 53.1 7.2 84314.7 399001.4 239.3
276 |
277 |3 -1.2 -0.5 0.6 52.8 6.5 67841.4 457682.8 209.5
278 |
279 |4 1.1 0.5 1.3 34.0 9.2 77573.8 352626.4 432.5
280 |
281 |5 -2.7 14.0 14.2 48.6 -144.9 79132.6 351080.7 985.0
282 |
283 |
284 |
285 +--------------------------------------------------------------------------+
286 | overall rms error: 4.46
287 |
288 +--------------------------------------------------------------------------+
289 The following menu then appears at the bottom of the monitor:
292 +-----+------------+------------------------------------------------+
295 |DONE | PRINT FILE | Double click on point to be included/excluded |
296 +-----+------------+------------------------------------------------+
297 The RMS error for the image is given under the column TITLEd "error"
300 and subTITLEd "east" and "north". In the above report, point number 1
301 is 0.0 and -0.9 meters (east and north) from the predicted location
302 calculated from the transformation equation. The RMS error for the
303 target map is listed under the heading "target". This is the RMS error
304 for the east and north coordinates of the target map but it is pre‐
305 sented in the table using one general value. The overall RMS error is
306 displayed at the bottom of the screen in meters. Points that create
307 high RMS error are displayed in red on the monitor (represented here in
308 italics).
309 The image coordinates of the point marked on the imagery group file is
311 given under the heading "image" and the subheadings "east" and "north".
312 The location of the control point in the target database is given under
313 the heading "control" and the subheadings "east","north", and "elev".
314 If you would like to exclude or include a control point, this can be
315 accomplished by placing the mouse cross hairs on the control point num‐
316 ber to be included (if the point is absent) or excluded (if the point
317 is displayed) and pressing the left button on the mouse twice. When a
318 point is excluded, it is not afterwards included in the calculation of
319 the RMS error, or included in the final rectification parameters. How‐
320 ever, it can be retrieved within photo.2target at any time by double
321 clicking with the mouse as described above.
322
324 To end the photo.2target program place the mouse cross hairs on the
325 word QUIT; the marked control points (including coordinates) will be
326 saved.
327
329 During the course of marking control points and computing the ortho-
330 rectification parameters, a matrix inversion error may occur. This is
331 caused by trying to invert a non-singular normal equation matrix. When
332 this situation arises, the status of all previously selected control
333 points are modified, the control points are excluded. Running
334 photo.init
335 for the selected imagery group with accurate camera exposure station
336 parameters should remedy the situation. The excluded control points
337 may again be included as described in the section ANALYZE.
338 A good rule of thumb is to mark at least 12 to 15 points which are
340 evenly distributed over the entire imagery group file in order to
341 obtain an accurate transformation parameters for the rectification
342 process. The RMS error may increase with more points added, but the
343 transformation parameters will be more accurate over the entire image.
344 An RMS error of less than or equal to approximately one resolution unit
346 (pixel) for the image being rectified is generally considered accept‐
347 able.
348
350 i.ortho.photo, photo.camera, photo.2image, photo.init, photo.rectify
351
353 Mike Baba, DBA Systems, Inc.
354 Last changed: $Date: 2006-12-15 11:10:21 +0100 (Fri, 15 Dec 2006) $
356 Full index
358 © 2003-2008 GRASS Development Team
360GRASS 6.3.0 photo.2target(1)