1photo.2target(1) Grass User's Manual photo.2target(1)
2
6 photo.2target - Create 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]
16 Parameters:
18 group=string
19 Name of imagery group
20 map=name
22 Name of image to be rectified which will be initialy drawn on
23 screen.
24 target=name
26 Name of a map from target mapset which will be initialy drawn on
27 screen.
28
30 photo.2target is an imagery function that enables you to mark control
31 points on an image to be ortho-rectified and then input the coordinates
32 of each point for calculation of rectification parameters. Rectifica‐
33 tion is the mapping of an image from one coordinate system to another.
34 The geometry of an image extracted into a GRASS LOCATION having an x,y
35 coordinate system is not planimetric. To create a planimetric image,
36 that is, to convert the x,y coordinate system into a standard coordi‐
37 nate system (for example, the UTM coordinate system or the State Plane
38 coordinate system), points from a map having the standard coordinates
39 must be associated with the same points on the image to be rectified.
40 The ortho-rectification parameters are computed in two phases. The
41 first phase computes a transformation matrix between image (row,col)
42 coordinates and photo (x,y) coordinates relative to the perspective
43 center. The transformation matrix is computed explicitly in the option
44 photo.2image . The second phase, photo.2target, enables you to mark
45 control points on the image and then input the standard coordinates
46 (Easting,Northing, and elevation) to determine the parameters for a
47 three dimensional projective transformation. photo.init
48 may be run before running photo.2target to modify the initial camera
49 exposure station parameters, and/or modify the standard deviation of
50 these parameters. photo.init
51 is not required but generally is helpful.
52 During the process of marking control points and entering standard
54 coordinates, you may compute the RMS (root mean square) error for each
55 control point entered. photo.2target does this by calculating the
56 transformation equation, and then plugging these results into an equa‐
57 tion for RMS error.
58 photo.2target offers a zoom option to locate precisely the point to be
60 marked on an image. This program also offers you the option of acquir‐
61 ing standard coordinates for a marked point from a map layer in the
62 target database, or from a digitizer.
63 To run photo.2target, a graphics monitor is required.
65 The procedure for marking points, entering coordinates, and calculating
67 RMS error is described below.
68 The terminal screen displays the following message:
70 use mouse now...
72 The graphics monitor displays the following screen:
74 +-----------------------------+--------------------------------+
77 |imagery filename (mag) | target filename (mag) |
78 +-----------------------------+--------------------------------+
79 | | |
80 | | |
81 | | |
82 | | |
83 | | |
84 | | |
85 | | |
86 +-----------------------------+--------------------------------+
87 | | |
88 | | |
89 | | |
90 | | |
91 | | |
92 | | |
93 +-----------------------------+--------------------------------+
94 |QUIT ZOOM PLOTCELL ANALYZE | |
95 +-----------------------------+--------------------------------+
96 A pop-down menu like that shown below will be superimposed on the left
99 half of the screen:
100 +----------------------------------------+
103 |Double click on cell file to be plotted |
104 | Double click here to cancel |
105 +----------------------------------------+
106 +--------------------+
107 | Mapset PERMANENT |
108 +---------+----------+
109 |gs13.1 | gs14.1 |
110 +---------+----------+
111 |gs21.1 | gs22.2 |
112 +---------+----------+
113 Any single file in the imagery group may be used to mark points, and
116 you can mark points on more than one file in the imagery group to accu‐
117 mulate the 12 points suggested minimum. Any file in the imagery group
118 can be rectified (using photo.rectify ) based on the rectification
119 parameters computed from these control points.
120 The imagery file you select is displayed in the upper left quadrant of
122 the screen.
123
125 To magnify the displayed file, you must place the mouse cross hairs on
126 the word ZOOM. The following menu will then be displayed at the bottom
127 of the screen:
128 +-------+-----+-------++--------------------+
131 |Cancel | Box | Point ||Select type of ZOOM |
132 +-------+-----+-------++--------------------+
133 You may identifying the zoom window either by using the mouse to make a
136 box, or by using the mouse to mark the center of the window and enter‐
137 ing a magnification factor. The terminal screen will display a mouse
138 button menu to guide you in identifying the window.
139 It is also possible to start zoom by box with middle mouse button and
141 pan by right mouse button.
142
144 To mark the points on the image that correspond to the points on a
145 standard coordinate system map, you must place the mouse cross hairs on
146 the corresponding location on the image to be marked and press the left
147 hand button on the mouse. A diamond shaped symbol will be marked on
148 the image. The terminal will display the following menu:
149 +------------------------------------+--------------------------+
152 |Point 1 marked at IMAGE COORDINATES | |
153 |IMAGE X: 1023.77 | |
154 |IMAGE Y: -164.41 | |
155 | | |
156 +------------------------------------+--------------------------+
157 |Enter CONTROL COORDINATES as east,north,elevation: |
158 +---------------------------------------------------------------+
159 You then enter the easting, northing, and elevation for the point
162 marked on the image. If you wish not to enter a coordinate, simply hit
163 RETURN to return control to the mouse; the marked point then disap‐
164 pears.
165 Entered point can be canceled by right mouse button click.
167
169 In addition to acquiring control points from a standard map, you have
170 the option of acquiring the points from a cell-map in the target data‐
171 base. The database map is displayed by placing the mouse cross hairs
172 on the words PLOT CELL. The following line is then displayed at the
173 bottom of the monitor:
174 +-------+---------------------------------------+
177 |Cancel | Indicate which side should be plotted |
178 +-------+---------------------------------------+
179 Which side of the monitor is to be plotted is indicated by placing the
182 mouse cross hairs on the half of the monitor screen that you would like
183 to use, and pressing the left mouse button. The following pop-down
184 menu will be superimposed on the half of the screen that was chosen:
185 +----------------------------------------+
188 |Double click on cell file to be plotted |
189 | Double click here to cancel |
190 +----------------------------------------+
191 +-----------------------------+
193 | Mapset user1 |
194 +--------------+--------------+
195 |tm.rectified | |
196 +--------------+--------------+
197 |tm.classified | |
198 +--------------+--------------+
199 | Mapset PERMANENT |
200 +--------------+--------------+
201 |elevation | geology |
202 +--------------+--------------+
203 |slope | soils |
204 +--------------+--------------+
205 |aspect | |
206 +--------------+--------------+
207 |roads | |
208 +--------------+--------------+
209 |streams | |
210 +--------------+--------------+
211 |airfields | |
212 +--------------+--------------+
213 After the map is displayed the following message appears at the bottom
216 of the monitor:
217 +-----------------+----------+--------+
220 |input method -> | keyboard | screen |
221 +-----------------+----------+--------+
222 If you wish to use the plotted map only as a comparative reference, the
225 keyboard can be chosen as the means to input coordinates corresponding
226 to the marked control points. This is done by placing the mouse cross
227 hairs on the word KEYBOARD and pressing the left button on the mouse.
228 If you select the SCREEN option, points marked on the image will auto‐
230 matically be associated with the coordinates from the corresponding
231 points on the target database map, and a corresponding elevation from
232 the cell-file selected for elevation data. In this option, when you
233 mark a point on the image, the following menu is displayed on the ter‐
234 minal:
235 +------------------------------------+--------------------------+
238 |Point 5 marked at IMAGE COORDINATES | |
239 |IMAGE X: 1023.77 | |
240 |IMAGE Y: -164.41 | |
241 | | |
242 | | |
243 |Control Point location | |
244 |East: 679132.57 | |
245 |North: 4351080.67 | |
246 |Elevation: 1010.00 | |
247 | | |
248 | | |
249 | | |
250 +------------------------------------+--------------------------+
251 |use mouse now... |
252 +---------------------------------------------------------------+
253 The coordinates for the target database map are automatically saved as
256 the coordinates corresponding to the marked control point on the image.
257
259 After a number of points have been marked (4 to 7), you can check the
260 RMS error of the points marked on the image. This is done by placing
261 the mouse cross hairs on the word ANALYZE at the bottom of the monitor.
262 An error report resembling that shown below is superimposed on the mon‐
263 itor:
264 +--------------------------------------------------------------------------+
267 | error
268 |
269 |# east north target east north east north elev.
270 |
271 +--------------------------------------------------------------------------+
272 |1 0.0 -0.9 1.0 48.5 4.8 79132.5 351080.6 10.0
273 |
274 |2 0.4 1.0 1.3 53.1 7.2 84314.7 399001.4 239.3
275 |
276 |3 -1.2 -0.5 0.6 52.8 6.5 67841.4 457682.8 209.5
277 |
278 |4 1.1 0.5 1.3 34.0 9.2 77573.8 352626.4 432.5
279 |
280 |5 -2.7 14.0 14.2 48.6 -144.9 79132.6 351080.7 985.0
281 |
282 |
283 |
284 +--------------------------------------------------------------------------+
285 | overall rms error: 4.46
286 |
287 +--------------------------------------------------------------------------+
288 The following menu then appears at the bottom of the monitor:
291 +-----+------------+------------------------------------------------+
294 |DONE | PRINT FILE | Double click on point to be included/excluded |
295 +-----+------------+------------------------------------------------+
296 The RMS error for the image is given under the column TITLEd "error"
299 and subTITLEd "east" and "north". In the above report, point number 1
300 is 0.0 and -0.9 meters (east and north) from the predicted location
301 calculated from the transformation equation. The RMS error for the
302 target map is listed under the heading "target". This is the RMS error
303 for the east and north coordinates of the target map but it is pre‐
304 sented in the table using one general value. The overall RMS error is
305 displayed at the bottom of the screen in meters. Points that create
306 high RMS error are displayed in red on the monitor (represented here in
307 italics).
308 The image coordinates of the point marked on the imagery group file is
310 given under the heading "image" and the subheadings "east" and "north".
311 The location of the control point in the target database is given under
312 the heading "control" and the subheadings "east","north", and "elev".
313 If you would like to exclude or include a control point, this can be
314 accomplished by placing the mouse cross hairs on the control point num‐
315 ber to be included (if the point is absent) or excluded (if the point
316 is displayed) and pressing the left button on the mouse twice. When a
317 point is excluded, it is not afterwards included in the calculation of
318 the RMS error, or included in the final rectification parameters. How‐
319 ever, it can be retrieved within photo.2target at any time by double
320 clicking with the mouse as described above.
321
323 To end the photo.2target program place the mouse cross hairs on the
324 word QUIT; the marked control points (including coordinates) will be
325 saved.
326
328 During the course of marking control points and computing the ortho-
329 rectification parameters, a matrix inversion error may occur. This is
330 caused by trying to invert a non-singular normal equation matrix. When
331 this situation arises, the status of all previously selected control
332 points are modified, the control points are excluded. Running
333 photo.init
334 for the selected imagery group with accurate camera exposure station
335 parameters should remedy the situation. The excluded control points
336 may again be included as described in the section ANALYZE.
337 A good rule of thumb is to mark at least 12 to 15 points which are
339 evenly distributed over the entire imagery group file in order to
340 obtain an accurate transformation parameters for the rectification
341 process. The RMS error may increase with more points added, but the
342 transformation parameters will be more accurate over the entire image.
343 An RMS error of less than or equal to approximately one resolution unit
345 (pixel) for the image being rectified is generally considered accept‐
346 able.
347
349 i.ortho.photo, photo.camera, photo.2image, photo.init, photo.rectify
350
352 Mike Baba, DBA Systems, Inc.
353 Last changed: $Date: 2006/04/21 12:56:35 $
355 Full index
357GRASS 6.2.2 photo.2target(1)