1i.rectify(1) Grass User's Manual i.rectify(1)
2
6 i.rectify - Rectifies an image by computing a coordinate transforma‐
7 tion for each pixel in the image based on the control points
8
10 imagery
11
13 i.rectify
14 i.rectify help
15 i.rectify [-ca] group=string [input=string[,string,...]] exten‐
16 sion=string order=integer [--verbose] [--quiet]
17 Flags:
19 -c
20 Use curr. region settings in target location (def.=calculate small‐
21 est area)
22 -a
24 Rectify all images in group
25 --verbose
27 Verbose module output
28 --quiet
30 Quiet module output
31 Parameters:
33 group=string
34 Name of imagery group
35 input=string[,string,...]
37 Name of input raster map(s)
38 extension=string
40 Output file extension (inputfile(s) + extension)
41 order=integer
43 Rectification polynom order (1-3)
44
46 i.rectify uses the control points identified in i.points or i.vpoints
47 to calculate a transformation matrix based on a first, second, or
48 third order polynomial and then converts x,y cell coordinates to stan‐
49 dard map coordinates for each pixel in the image. The result is a
50 planimetric image with a transformed coordinate system (i.e., a differ‐
51 ent coordinate system than before it was rectified).
52 i.points or i.vpoints must be run before i.rectify, and both programs
54 are required to rectify an image. An image must be rectified before it
55 can reside in a standard coordinate LOCATION, and therefore be analyzed
56 with the other map layers in the standard coordinate LOCATION. Upon
57 completion of i.rectify, the rectified image is deposited in the target
58 standard coordinate LOCATION. This LOCATION is selected using i.tar‐
59 get.
60
62 The first prompt in the program asks for the name of the group contain‐
63 ing the files to be rectified.
64 Enter the group containing files to be rectified
65 Enter 'list' for a list of existing imagery groups
66 Enter 'list -f' for a verbose listing
67 Hit RETURN to cancel request
68 >
69 This is the same imagery group that was selected in i.points or
70 i.vpoints and the group that contains the raster maps with the marked
71 points and their associated map coordinates. You are then asked to
72 select the raster map(s) within the group to be rectified:
73 Please select the file(s) to rectify by naming an output file
74 spot1.1 in mapsetname .............
75 spot1.2 in mapsetname .............
76 spot1.3 in mapsetname .............
77 spotclass1 in mapsetname spotrectify1.
78 spotreject1 in mapsetname .............
80 (enter list by any name to get a list of existing raster maps)
81 AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
82 (OR<Ctrl-C> TO CANCEL)
83 More than one raster map may be rectified at a time. Each cell file
84 should be given a unique output file name.
85 Next, you are asked to select one of two windows regions:
87 Please select one of the following options
88 1. Use the current window in the target location
89 2. Determine the smallest window which covers the image
90 >
91 The i.rectify program will only rectify that portion of the image or
92 raster map that occurs within the chosen window region, and only that
93 portion of the cell file will be relocated in the target database. It
94 is important therefore, to check the current mapset window in the tar‐
95 get LOCATION if choice number one is selected.
96 If you are rectifying a file with plans to patch it to another file
98 using the GRASS program r.patch, choose option number one, the current
99 window in the target location. This window, however, must be the
100 default window for the target LOCATION. When a file being rectified is
101 smaller than the default window in which it is being rectified, zeros
102 are added to the rectified file. Patching files of the same size that
103 contain 0/non-zero data, eliminates the possibility of a no-data line
104 the patched result. This is because, when the images are patched, the
105 zeros in the image are "covered" with non-zero pixel values. When rec‐
106 tifying files that are going to be patched, rectify all of the files
107 using the same default window.
108 Select the order of transformation desired with the order option:
110 1st Order 2nd Order 3rd Order
111 The program will immediately recalculate the RMSE and the number of
112 points required.
113 Linear affine transformation (1st order transformation)
115 x' = ax + by +c
116 y' = Ax + Bt +C
117 The a,b,c,A,B,C are determined by least squares regression based on the
119 control points entered. This transformation applies scaling, transla‐
120 tion and rotation. It is NOT a general purpose rubber-sheeting, nor is
121 it ortho-photo rectification using a DEM, not second order polynomial,
122 etc. It can be used if (1) you have geometrically correct images, and
123 (2) the terrain or camera distortion effect can be ignored.
124 Polynomial Transformation Matrix (2nd, 3d order transformation)
126 The ANALYZE function has been changed to support calculating the regis‐
127 tration coefficients using a first, second, or third order transforma‐
128 tion matrix. The number of control points required for a selected
129 order of transformation (represented by n) is
130 ((n + 1) * (n + 2) / 2)
131 or 3, 6, and 10 respectively. It is strongly recommended that one or
133 more additional points be identified to allow for an overly- determined
134 transformation calculation which will generate the Root Mean Square
135 (RMS) error values for each included point. The RMS error values for
136 all the included control points are immediately recalculated when the
137 user selects a different transformation order from the menu bar. The
138 polynomial equations are performed using a modified Gaussian elimina‐
139 tion method.
140 Program Execution
142 Note: The rectified image or rectified raster maps will be located in
143 the target LOCATION when the program is completed. The original unrec‐
144 tified files are not modified or removed.
145
147 i.rectify uses nearest neighbor resampling during the transformation
148 choosing the actual pixel that has its centre nearest to the point
149 location in the image. Advantage of this method is that the pixel
150 brightness of the image is kept as i.rectify rearranges the geometry of
151 the image pixels.
152 If i.rectify starts normally but after some time the following text is
154 seen:
155 GIS ERROR: error while writing to temp file
156 the user may try the flag -c (or the module needs more free space on
157 the hard drive).
158
160 The GRASS 4 Image Processing manual
161 g.transform, r.proj, v.proj, i.group, i.points, i.vpoints, i.target
163
165 William R. Enslin, Michigan State University, Center for Remote Sensing
166 Modified for GRASS 5.0 by:
168 Luca Palmeri (palmeri@ux1.unipd.it)
169 Bill Hughes
170 Pierre de Mouveaux (pmx@audiovu.com)
171 CMD mode by Bob Covill
172 Last changed: $Date: 2007-06-14 14:18:14 +0200 (Thu, 14 Jun 2007) $
174 Full index
176 © 2003-2008 GRASS Development Team
178GRASS 6.3.0 i.rectify(1)