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<EM>i.photo.2image</EM> is an imagery function that enables
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you to mark fiducial or reseau points on an image to be
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ortho-rectified and then computes the image-to-photo
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coordinate transformation parameters. The coordinates of
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the fiducials or reseau marks can be chosen for a camera
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During the process of marking reference points with known
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photo coordinates, you may compute the RMS (root mean
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square) error for each reference point entered.
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<EM>i.photo.2image</EM> does this by calculating the
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transformation equation (the same one that is calculated by
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<EM><A HREF="i.points.html">i.points</A> </EM>),
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and then plugging these results into an equation for RMS
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<EM>i.photo.2image</EM> offers a zoom option to locate
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precisely the fiducial or reseau point to be marked on an
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To run <EM>i.photo.2image</EM>, a graphics monitor is
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The procedure for marking fiducial or reseau points,
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entering known photo-coordinates, and analyzing the RMS
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error is described below.
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The terminal screen displays this message:
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<B>use mouse now...</B>
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The graphics monitor displays the following screen:
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+---------------------------+---------------------------------+
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+---------------------------+---------------------------------+
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+---------------------------+---------------------------------+
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+---------------------------+---------------------------------+
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+---------------------------+---------------------------------+
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A pop-down menu like that shown below will be superimposed on the
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left half of the screen:
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+------------------------------------------+
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| Double click on raster map to be plotted |
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| Double click here to cancel |
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+------------------------------------------+
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Any single file in the imagery group may be used on which to mark
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points, and you may mark points on more than one file
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in the imagery group to accumulate the suggested minimum number of
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4-8 fiducial or ressue points.
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The imagery file selected is displayed in the upper
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left quadrant of the screen.
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The camera reference file may be viewed by placing the mouse
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cross hairs on the words CAMERA. The camera reference file
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will be displayed in the lower left quadrant of the display:
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|---------------------------------------------------------------|
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|Camera Reference File |
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|---------------------------------------------------------------|
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| CAMERA NAME : camera name |
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| CAMERA ID : L1234 |
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| CAMERA CFL : 153.021 mm. |
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| CAMERA XP : 0.050 mm. |
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| CAMERA XP : 0.056 mm. |
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|---------------------------------------------------------------|
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|ID (X PHOTO) mm. (Y PHOTO) mm. |
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|_______________________________________________________________|
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|1 -105.023 110.123 |
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|3 110.965 -104.329 |
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|4 -103.932 -110.352 |
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|_______________________________________________________________|
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The following menu is displayed at the bottom
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of the graphics display:
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+-----+------+-----------+--------+---------+-------------------+-------------+
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|Quit | Zoom | Plot Cell | Camera | Analyze | Input->KEYBOARD | CAMERA FILE |
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+-----+------+-----------+--------+---------+-------------------+-------------+
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To magnify the displayed file, you must
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place the mouse cross hairs on the word ZOOM. The following menu
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will then be displayed at the bottom of the screen:
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+-------+-----+-------++--------------------+
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|Cancel | Box | Point ||Select type of ZOOM |
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+-------+-----+-------++--------------------+
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You have the option of identifying the zoom window either by using
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the mouse to make a box, or by using the mouse to mark the center
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of the desired window, and adjusting the magnification factor.
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The terminal screen will display a mouse button menu to guide you in
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identifying the window. The section of the image within the zoom window
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will be displayed in the upper right hand quadrant.
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<H2>MARKING REFERENCE POINTS</H2>
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To mark the known reference points (fiducial marks, reseau marks, etc.)
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on the image, you must place the mouse cross hairs
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on the corresponding location on the image to be marked and press
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the left hand button on the mouse. A diamond shaped symbol will be marked
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If you wish to use the camera reference file only as a
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comparative reference, then the keyboard can be chosen as
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the means to input photo coordinates corresponding to the marked
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reference points on the image. This is done by placing the mouse
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cross hairs on the word KEYBOARD and pressing the left
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The following menu is displayed on the graphics terminal:
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+------------------------------------+--------------------------+
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|Point 1 marked at IMAGE COORDINATES | |
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+------------------------------------+--------------------------+
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|Enter PHOTO COORDINATES as x and y: |
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+---------------------------------------------------------------+
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You then enter the known (x,y) photo coordinates, relative
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to the perspective center, for the reference
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point marked on the image. If you
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do not wish to enter a coordinate, simply hit RETURN to continue;
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the marked reference point will disappear.
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If you select the CAMERA FILE option, then reference points
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marked on the image will be associated with selected photo
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coordinates from the displayed camera reference file. In this option,
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when you mark a point on the image, the following menu is
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displayed on the graphics terminal:
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-------------------------------------------------------------
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CANCEL Double click on the fiducial mark to be referenced
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-------------------------------------------------------------
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If you would like to select the photo coordinates of a displayed
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reference mark, this can be accomplished by placing the mouse
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cross hairs on the reference point to be selected and pressing
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the left button on the mouse twice. After a reference point is selected
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from the display, you are prompted with "Look ok? (Y/N)".
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If you respond with no, the reference point is ignored.
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If you respond with yes, the following is displayed on the terminal:
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+----------------------------------------+--------------------------+
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|Point 1 marked at IMAGE COORDINATES | |
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|Point 1 referenced at PHOTO COORDINATES | |
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+----------------------------------------+--------------------------+
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+----------------------------------------+--------------------------+
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The photo coordinates and the corresponding image coordinates are
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automatically saved in the photo_points file associated with the imagery
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After a number of points have been marked (4 to 8), you can
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check the RMS error of the points marked on the image. This is done
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by placing the mouse cross hairs on the word ANALYZE at the bottom
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of the monitor. An error report resembling the one shown below
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is superimposed on the monitor:
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+--------------------------------------------------------------------+
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| error image photo |
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|# row col photo east north x y |
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|1 0.0 -0.9 1.0 1048.5 -144.8 -105.023 110.122 |
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|2 0.4 1.0 1.3 2153.1 -567.2 107.987 109.834 |
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|3 -1.2 -0.5 0.6 1452.8 -476.5 110.965 -104.329 |
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|4 1.1 0.5 1.3 1034.0 -109.2 -103.932 -110.352 |
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+--------------------------------------------------------------------+
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| overall rms error: 4.46 |
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+--------------------------------------------------------------------+
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The following menu then appears at the bottom of the monitor:
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+-----+-------+------+-----------------------------------------------+
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|DONE | PRINT | FILE | Double click on point to be included/excluded |
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+-----+-------+------+-----------------------------------------------+
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The RMS error for the image is given under the column
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TITLEd "error" and subTITLEd "row" and "col". In the above
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report, point number 1 is 0.0 rows and -0.9 columns from
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the predicted location calculated from the transformation
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equation. The RMS error for the photo coordinates is
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listed under the heading "photo". This is the RMS error
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for the x and y coordinates of the photo coordinates but it
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is presented in the table using one general value. The
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overall RMS error is displayed at the bottom of the screen
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in milimeters. Points that create high RMS error are
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displayed in red on the monitor (represented here in
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The location of the point marked on the imagery group file
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is given under the heading "image" and the subheadings
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"east" and "north". The location of the point in the photo
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coordinates is given under the heading "photo" and the
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subheadings "x" and "y". If you would like to exclude or
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include a point, this can be accomplished by placing the
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mouse cross hairs on the point number to be included (if
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the point is absent) or excluded (if the point is
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displayed) and pressing the left button on the mouse
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twice. When a point is excluded, it is not afterwards
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included in the calculation of the RMS error, or included
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in the final transformation matrix. However, it can be
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retrieved within <EM>i.photo.2image</EM> at any time by
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double clicking with the mouse as described above.
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To end the <EM>i.photo.2image</EM> program place the mouse cross hairs
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on the word QUIT; the marked reference points (including coordinates)
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A good rule of thumb is to mark at least 4 to 8 points which are
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evenly distributed over the perimeter of the imagery
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group file in order to obtain
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an accurate transformation equation for the rectification process.
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The RMS error may increase with more points added, but the
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transformation equation will be more accurate.
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An RMS error of less than or equal to approximately one resolution
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unit (pixel) for the image being rectified is generally considered
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<A HREF="i.ortho.photo.html">i.ortho.photo</A>,
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<A HREF="i.photo.camera.html">i.photo.camera</A>,
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<A HREF="i.photo.2target.html">i.photo.2target</A>,
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<A HREF="i.photo.init.html">i.photo.init</A>,
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<A HREF="i.photo.rectify.html">i.photo.rectify</A>
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Mike Baba, DBA Systems, Inc.
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<i>Last changed: $Date: 2012-02-25 14:38:11 +0100 (Sat, 25 Feb 2012) $</i>