NAME¶
i.photo.2image - Interactively mark fiducial or reseau points on
an image.
KEYWORDS¶
imagery, orthorectify
SYNOPSIS¶
i.photo.2image
i.photo.2image help
i.photo.2image group=
name [--
verbose] [--
quiet]
Parameters:¶
- group=name
-
Name of imagery group for ortho-rectification
DESCRIPTION¶
i.photo.2image is an imagery function that enables you to mark fiducial
or reseau points on an image to be ortho-rectified and then computes the
image-to-photo coordinate transformation parameters. The coordinates of the
fiducials or reseau marks can be choosen for a camera reference file.
During the process of marking reference points with known photo coordinates, you
may compute the RMS (root mean square) error for each reference point entered.
i.photo.2image does this by calculating the transformation equation
(the same one that is calculated by
i.points ), and then plugging these
results into an equation for RMS error.
i.photo.2image offers a zoom option to locate precisely the fiducial or
reseau point to be marked on an image.
To run
i.photo.2image, a graphics monitor is required.
The procedure for marking fiducial or reseau points, entering known
photo-coordinates, and analyzing the RMS error is described below.
The terminal screen displays this message:
use mouse now...
The graphics monitor displays the following screen:
+---------------------------+---------------------------------+
|imagery | |
+---------------------------+---------------------------------+
| | |
| | |
| | |
| | |
| | |
| | |
| | |
+---------------------------+---------------------------------+
| | |
| | |
| | |
| | |
| | |
| | |
| | |
+---------------------------+---------------------------------+
| | |
+---------------------------+---------------------------------+
A pop-down menu like that shown below will be superimposed on the left half of
the screen:
+------------------------------------------+
| Double click on raster map to be plotted |
| Double click here to cancel |
+------------------------------------------+
+----------------+
|Mapset imagery |
+-------+--------+
|gs13.1 | gs21.1 |
+-------+--------+
|gs14.1 | gs22.2 |
+-------+--------+
Any single file in the imagery group may be used on which to mark points, and
you may mark points on more than one file in the imagery group to accumulate
the suggested minimum number of 4-8 fiducial or ressue points. The imagery
file selected is displayed in the upper left quadrant of the screen.
CAMERA FILE¶
The camera reference file may be viewed by placing the mouse cross hairs on the
words CAMERA. The camera reference file will be displayed in the lower left
quadrant of the display:
|---------------------------------------------------------------|
|Camera Reference File |
|---------------------------------------------------------------|
| CAMERA NAME : camera name |
| CAMERA ID : L1234 |
| CAMERA CFL : 153.021 mm. |
| CAMERA XP : 0.050 mm. |
| CAMERA XP : 0.056 mm. |
| number of fid. 4 |
|---------------------------------------------------------------|
| |
|ID (X PHOTO) mm. (Y PHOTO) mm. |
|_______________________________________________________________|
|1 -105.023 110.123 |
|2 107.987 109.834 |
|3 110.965 -104.329 |
|4 -103.932 -110.352 |
|_______________________________________________________________|
The following menu is displayed at the bottom of the graphics display:
+-----+------+-----------+--------+---------+-------------------+-------------+
|Quit | Zoom | Plot Cell | Camera | Analyze | Input->KEYBOARD | CAMERA FILE |
+-----+------+-----------+--------+---------+-------------------+-------------+
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 |
+-------+-----+-------++--------------------+
You have the option of identifying the zoom window either by using the mouse to
make a box, or by using the mouse to mark the center of the desired window,
and adjusting the magnification factor. The terminal screen will display a
mouse button menu to guide you in identifying the window. The section of the
image within the zoom window will be displayed in the upper right hand
quadrant.
MARKING REFERENCE POINTS¶
To mark the known reference points (fiducial marks, reseau marks, etc.) on the
image, 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.
If you wish to use the camera reference file only as a comparative reference,
then the keyboard can be chosen as the means to input photo coordinates
corresponding to the marked reference points on the image. This is done by
placing the mouse cross hairs on the word KEYBOARD and pressing the left
button on the mouse.
The following menu is displayed on the graphics terminal:
+------------------------------------+--------------------------+
|Point 1 marked at IMAGE COORDINATES | |
|east: 1023.77 | |
|north: 506.56 | |
| | |
| | |
| | |
| | |
| | |
+------------------------------------+--------------------------+
|Enter PHOTO COORDINATES as x and y: |
+---------------------------------------------------------------+
You then enter the known (x,y) photo coordinates, relative to the perspective
center, for the reference point marked on the image. If you do not wish to
enter a coordinate, simply hit RETURN to continue; the marked reference point
will disappear.
If you select the CAMERA FILE option, then reference points marked on the image
will be associated with selected photo coordinates from the displayed camera
reference file. In this option, when you mark a point on the image, the
following menu is displayed on the graphics terminal:
-------------------------------------------------------------
CANCEL Double click on the fiducial mark to be referenced
-------------------------------------------------------------
If you would like to select the photo coordinates of a displayed reference mark,
this can be accomplished by placing the mouse cross hairs on the reference
point to be selected and pressing the left button on the mouse twice. After a
reference point is selected from the display, you are prompted with "Look
ok? (Y/N)". If you respond with no, the reference point is ignored. If
you respond with yes, the following is displayed on the terminal:
+----------------------------------------+--------------------------+
|Point 1 marked at IMAGE COORDINATES | |
|east: 1023.77 | |
|north: 1065.41 | |
| | |
| | |
|Point 1 referenced at PHOTO COORDINATES | |
|X: -105.023 | |
|Y: 110.122 | |
| | |
| | |
| | |
| | |
| | |
+----------------------------------------+--------------------------+
| use mouse now... |
+----------------------------------------+--------------------------+
The photo coordinates and the corresponding image coordinates are automatically
saved in the photo_points file associated with the imagery group.
ANALYZE¶
After a number of points have been marked (4 to 8), 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 the one shown below is superimposed on the monitor:
+--------------------------------------------------------------------+
| error image photo |
| |
|# row col photo east north x y |
|1 0.0 -0.9 1.0 1048.5 -144.8 -105.023 110.122 |
|2 0.4 1.0 1.3 2153.1 -567.2 107.987 109.834 |
|3 -1.2 -0.5 0.6 1452.8 -476.5 110.965 -104.329 |
|4 1.1 0.5 1.3 1034.0 -109.2 -103.932 -110.352 |
| |
+--------------------------------------------------------------------+
| overall rms error: 4.46 |
+--------------------------------------------------------------------+
The following menu then appears at the bottom of the monitor:
+-----+-------+------+-----------------------------------------------+
|DONE | PRINT | FILE | Double click on point to be included/excluded |
+-----+-------+------+-----------------------------------------------+
The RMS error for the image is given under the column TITLEd "error"
and subTITLEd "row" and "col". In the above report, point
number 1 is 0.0 rows and -0.9 columns from the predicted location calculated
from the transformation equation. The RMS error for the photo coordinates is
listed under the heading "photo". This is the RMS error for the x
and y coordinates of the photo coordinates but it is presented in the table
using one general value. The overall RMS error is displayed at the bottom of
the screen in milimeters. Points that create high RMS error are displayed in
red on the monitor (represented here in italics).
The location of the point marked on the imagery group file is given under the
heading "image" and the subheadings "east" and
"north". The location of the point in the photo coordinates is given
under the heading "photo" and the subheadings "x" and
"y". If you would like to exclude or include a point, this can be
accomplished by placing the mouse cross hairs on the point number to be
included (if the point is absent) or excluded (if the point is displayed) and
pressing the left button on the mouse twice. When a point is excluded, it is
not afterwards included in the calculation of the RMS error, or included in
the final transformation matrix. However, it can be retrieved within
i.photo.2image at any time by double clicking with the mouse as
described above.
QUIT¶
To end the
i.photo.2image program place the mouse cross hairs on the word
QUIT; the marked reference points (including coordinates) will be saved.
NOTES¶
A good rule of thumb is to mark at least 4 to 8 points which are evenly
distributed over the perimeter of the imagery group file in order to obtain an
accurate transformation equation for the rectification process. The RMS error
may increase with more points added, but the transformation equation will be
more accurate.
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.2target,
i.photo.init, i.photo.rectify
AUTHOR¶
Mike Baba, DBA Systems, Inc.
Last changed: $Date: 2010-12-22 11:05:10 +0100 (Wed, 22 Dec 2010) $
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