other versions
- jessie 6.4.4-1
i.photo.2target(1grass) | Grass User's Manual | i.photo.2target(1grass) |
NAME¶
i.photo.2target - Creates control points on an image to be ortho-rectified.KEYWORDS¶
imagery, orthorectifySYNOPSIS¶
i.photo.2targetParameters:¶
- group=string
-
- map=name
-
- target=name
-
DESCRIPTION¶
i.photo.2target is an imagery function that enables you to mark control points on an image to be ortho-rectified and then input the coordinates of each point for calculation of rectification parameters. Rectification is the mapping of an image from one coordinate system to another. The geometry of an image extracted into a GRASS LOCATION having an x,y coordinate system is not planimetric. To create a planimetric image, that is, to convert the x,y coordinate system into a standard coordinate system (for example, the UTM coordinate system or the State Plane coordinate system), points from a map having the standard coordinates must be associated with the same points on the image to be rectified. The ortho-rectification parameters are computed in two phases. The first phase computes a transformation matrix between image (row,col) coordinates and photo (x,y) coordinates relative to the perspective center. The transformation matrix is computed explicitly in the option i.photo.2image . The second phase, i.photo.2target, enables you to mark control points on the image and then input the standard coordinates (Easting,Northing, and elevation) to determine the parameters for a three dimensional projective transformation. i.photo.init may be run before running i.photo.2target to modify the initial camera exposure station parameters, and/or modify the standard deviation of these parameters. i.photo.init is not required but generally is helpful. During the process of marking control points and entering standard coordinates, you may compute the RMS (root mean square) error for each control point entered. i.photo.2target does this by calculating the transformation equation, and then plugging these results into an equation for RMS error. i.photo.2target offers a zoom option to locate precisely the point to be marked on an image. This program also offers you the option of acquiring standard coordinates for a marked point from a map layer in the target database, or from a digitizer. To run i.photo.2target, a graphics monitor is required. The procedure for marking points, entering coordinates, and calculating RMS error is described below. The terminal screen displays the following message: use mouse now... The graphics monitor displays the following screen:+------------------------------------------+
| Double click on raster map to be plotted |
| Double click here to cancel |
+------------------------------------------+
+--------------------+
| Mapset PERMANENT |
+---------+----------+
|gs13.1 | gs14.1 |
+---------+----------+
|gs21.1 | gs22.2 |
+---------+----------+
ZOOM¶
To magnify the displayed file, you must place the mouse cross hairs on the word ZOOM. The following menu will then be displayed at the bottom of the screen:+-------+-----+-------++--------------------+
|Cancel | Box | Point ||Select type of ZOOM |
+-------+-----+-------++--------------------+
MARKING POINTS¶
To mark the points on the image that correspond to the points on a standard coordinate system map, you must place the mouse cross hairs on the corresponding location on the image to be marked and press the left hand button on the mouse. A diamond shaped symbol will be marked on the image. The terminal will display the following menu:+------------------------------------+--------------------------+
|Point 1 marked at IMAGE COORDINATES | |
|IMAGE X: 1023.77 | |
|IMAGE Y: -164.41 | |
| | |
+------------------------------------+--------------------------+
|Enter CONTROL COORDINATES as east,north,elevation: |
+---------------------------------------------------------------+
PLOT CELL¶
In addition to acquiring control points from a standard map, you have the option of acquiring the points from a cell-map in the target database. The database map is displayed by placing the mouse cross hairs on the words PLOT CELL. The following line is then displayed at the bottom of the monitor:+-------+---------------------------------------+
|Cancel | Indicate which side should be plotted |
+-------+---------------------------------------+
+------------------------------------------+
| Double click on raster map to be plotted |
| Double click here to cancel |
+------------------------------------------+
+-----------------------------+
| Mapset user1 |
+--------------+--------------+
|tm.rectified | |
+--------------+--------------+
|tm.classified | |
+--------------+--------------+
| Mapset PERMANENT |
+--------------+--------------+
|elevation | geology |
+--------------+--------------+
|slope | soils |
+--------------+--------------+
|aspect | |
+--------------+--------------+
|roads | |
+--------------+--------------+
|streams | |
+--------------+--------------+
|airfields | |
+--------------+--------------+
+-----------------+----------+--------+
|input method -> | keyboard | screen |
+-----------------+----------+--------+
+------------------------------------+--------------------------+
|Point 5 marked at IMAGE COORDINATES | |
|IMAGE X: 1023.77 | |
|IMAGE Y: -164.41 | |
| | |
| | |
|Control Point location | |
|East: 679132.57 | |
|North: 4351080.67 | |
|Elevation: 1010.00 | |
| | |
| | |
| | |
+------------------------------------+--------------------------+
|use mouse now... |
+---------------------------------------------------------------+
ANALYZE¶
After a number of points have been marked (4 to 7), you can check the RMS error of the points marked on the image. This is done by placing the mouse cross hairs on the word ANALYZE at the bottom of the monitor. An error report resembling that shown below is superimposed on the monitor:+-----+------------+------------------------------------------------+
|DONE | PRINT FILE | Double click on point to be included/excluded |
+-----+------------+------------------------------------------------+
QUIT¶
To end the i.photo.2target program place the mouse cross hairs on the word QUIT; the marked control points (including coordinates) will be saved.NOTES¶
During the course of marking control points and computing the ortho-rectification parameters, a matrix inversion error may occur. This is caused by trying to invert a non-singular normal equation matrix. When this situation arises, the status of all previously selected control points are modified, the control points are excluded. Running i.photo.init for the selected imagery group with accurate camera exposure station parameters should remedy the situation. The excluded control points may again be included as described in the section ANALYZE. A good rule of thumb is to mark at least 12 to 15 points which are evenly distributed over the entire imagery group file in order to obtain an accurate transformation parameters for the rectification process. The RMS error may increase with more points added, but the transformation parameters will be more accurate over the entire image. An RMS error of less than or equal to approximately one resolution unit (pixel) for the image being rectified is generally considered acceptable.SEE ALSO¶
i.ortho.photo, i.photo.camera, i.photo.2image, i.photo.init, i.photo.rectifyAUTHOR¶
Mike Baba, DBA Systems, Inc. Last changed: $Date: 2010-12-22 11:05:10 +0100 (Wed, 22 Dec 2010) $ Full index © 2003-2014 GRASS Development TeamGRASS 6.4.4 |