photo.2target(1)	      Grass User's Manual	      photo.2target(1)



_T_h_i_s _i_s _n_o_t _a _c_o_m_m_a_n_d _i_n _i_t_s_e_l_f_, _b_u_t _a_n _o_p_t_i_o_n _t_o _t_h_e _c_o_m_m_a_n_d _i_._o_r_t_h_o_._p_h_o_t_o

NNAAMMEE
       _p_h_o_t_o_._2_t_a_r_g_e_t  -  An  imagery function that enables you to mark control
       points on an image to be ortho-rectified, and  then  input  the	ground
       coordinates of each control point for determination of ortho-rectifica-
       tion parameters. This  establishes  the	absolute  orientation  between
       image pixels and ground coordinates. The ortho-rectification parameters
       are required as input for the GRASS program
	_p_h_o_t_o_._r_e_c_t_i_f_y .
       _(_G_R_A_S_S _I_m_a_g_e_r_y _P_r_o_c_e_s_s_i_n_g _T_o_o_l_)

SSYYNNOOPPSSIISS
       Selected from _i_._o_r_t_h_o_._p_h_o_t_o

DDEESSCCRRIIPPTTIIOONN
       _p_h_o_t_o_._2_t_a_r_g_e_t 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.   Rectifica-
       tion  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  coordi-
       nate  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
       _p_h_o_t_o_._2_i_m_a_g_e .  The second phase, _p_h_o_t_o_._2_t_a_r_g_e_t, 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.  _p_h_o_t_o_._i_n_i_t
	may  be  run before running _p_h_o_t_o_._2_t_a_r_g_e_t to modify the initial camera
       exposure station parameters, and/or modify the  standard  deviation  of
       these parameters.  _p_h_o_t_o_._i_n_i_t
	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.   photo.2target  does  this by calculating the
       transformation equation, and then plugging these results into an  equa-
       tion for RMS error.


       _p_h_o_t_o_._2_t_a_r_g_e_t  offers a zoom option to locate precisely the point to be
       marked on an image. This program also offers you the option of  acquir-
       ing  standard  coordinates  for	a marked point from a map layer in the
       target database, or from a digitizer.


       To run _p_h_o_t_o_._2_t_a_r_g_e_t, 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:


       uussee mmoouussee nnooww......


       The graphics monitor displays the following screen:



       +-----------------------------+--------------------------------+
       |imagery  filename  (mag)     | target  filename  (mag)	      |
       +-----------------------------+--------------------------------+
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       +-----------------------------+--------------------------------+
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       |			     |				      |
       +-----------------------------+--------------------------------+
       |QUIT ZOOM PLOTCELL ANALYZE   |				      |
       +-----------------------------+--------------------------------+



       A  pop-down menu like that shown below will be superimposed on the left
       half of the screen:



		  +----------------------------------------+
		  |Double click on cell file to be plotted |
		  | Double click here to cancel 	   |
		  +----------------------------------------+
			      +--------------------+
			      |  Mapset PERMANENT  |
			      +---------+----------+
			      |gs13.1	| gs14.1   |
			      +---------+----------+
			      |gs21.1	| gs22.2   |
			      +---------+----------+




       Any single file in the imagery group may be used to  mark  points,  and
       you can mark points on more than one file in the imagery group to accu-
       mulate the 12 points suggested minimum.	Any file in the imagery  group
       can  be	rectified  (using  _p_h_o_t_o_._r_e_c_t_i_f_y  ) based on the rectification
       parameters computed from these control points.


       The imagery file you select is displayed in the upper left quadrant  of
       the screen.

ZZOOOOMM
       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 may identifying the zoom window either by using the mouse to make a
       box, or by using the mouse to mark the center of the window and	enter-
       ing  a  magnification factor.  The terminal screen will display a mouse
       button menu to guide you in identifying the window.



MMAARRKKIINNGG PPOOIINNTTSS
       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:		  |
	  +---------------------------------------------------------------+



       You then enter the easting,  northing,  and  elevation  for  the  point
       marked on the image.  If you wish not to enter a coordinate, simply hit
       RETURN to return control to the mouse;  the marked  point  then	disap-
       pears.



PPLLOOTT CCEELLLL
       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 data-
       base.   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 |
	   +-------+---------------------------------------+



       Which  side of the monitor is to be plotted is indicated by placing the
       mouse cross hairs on the half of the monitor screen that you would like
       to  use,  and  pressing	the left mouse button.	The following pop-down
       menu will be superimposed on the half of the screen that was chosen:



	   +----------------------------------------+
	   |Double click on cell file to be plotted |
	   | Double click here to cancel	    |
	   +----------------------------------------+

	   +-----------------------------+
	   |   Mapset user1		 |
	   +--------------+--------------+
	   |tm.rectified  |		 |
	   +--------------+--------------+
	   |tm.classified |		 |
	   +--------------+--------------+
	   |   Mapset PERMANENT 	 |
	   +--------------+--------------+
	   |elevation	  | geology	 |
	   +--------------+--------------+
	   |slope	  | soils	 |
	   +--------------+--------------+
	   |aspect	  |		 |
	   +--------------+--------------+
	   |roads	  |		 |
	   +--------------+--------------+
	   |streams	  |		 |
	   +--------------+--------------+
	   |airfields	  |		 |
	   +--------------+--------------+



       After the map is displayed the following message appears at the	bottom
       of the monitor:



	    +-----------------+----------+--------+
	    |input method ->  | keyboard | screen |
	    +-----------------+----------+--------+



       If you wish to use the plotted map only as a comparative reference, the
       keyboard can be chosen as the means to input coordinates  corresponding
       to  the marked control points.  This is done by placing the mouse cross
       hairs on the word KEYBOARD and pressing the left button on the mouse.


       If you select the SCREEN option, points marked on the image will  auto-
       matically  be  associated  with	the coordinates from the corresponding
       points on the target database map, and a corresponding  elevation  from
       the  cell-file  selected  for elevation data.  In this option, when you
       mark a point on the image, the following menu is displayed on the  ter-
       minal:



	  +------------------------------------+--------------------------+
	  |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...						  |
	  +---------------------------------------------------------------+



       The  coordinates for the target database map are automatically saved as
       the coordinates corresponding to the marked control point on the image.

AANNAALLYYZZEE
       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 mon-
       itor:



       +--------------------------------------------------------------------------+
       |								 error
       |
       |#  east    north    target    east    north    east    north	 elev.
       |
       +--------------------------------------------------------------------------+
       |1   0.0     -0.9       1.0     48.5	4.8   79132.5 351080.6	  10.0
       |
       |2  0.4	    1.0       1.3     53.1     7.2   84314.7 399001.4	 239.3
       |
       |3  -1.2     -0.5       0.6     52.8	6.5   67841.4 457682.8	 209.5
       |
       |4  1.1	    0.5       1.3     34.0     9.2   77573.8 352626.4	 432.5
       |
       |5  -2.7     14.0      14.2     48.6  -144.9   79132.6 351080.7	 985.0
       |
       |
       |
       +--------------------------------------------------------------------------+
       |		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 "east" and "north".  In the above report, point number 1
       is 0.0 and -0.9 meters (east and north)	from  the  predicted  location
       calculated  from  the  transformation  equation.  The RMS error for the
       target map is listed under the heading "target".  This is the RMS error
       for  the  east  and  north coordinates of the target map but it is pre-
       sented in the table using one general value.  The overall RMS error  is
       displayed  at  the  bottom of the screen in meters.  Points that create
       high RMS error are displayed in red on the monitor (represented here in
       italics).


       The  image coordinates 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 control point in the target database is given under
       the heading "control" and the subheadings "east","north",  and  "elev".
       If  you	would  like to exclude or include a control point, this can be
       accomplished by placing the mouse cross hairs on the control point num-
       ber  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 rectification parameters.  How-
       ever,  it  can  be retrieved within _p_h_o_t_o_._2_t_a_r_g_e_t at any time by double
       clicking with the mouse as described above.

QQUUIITT
       To end the _p_h_o_t_o_._2_t_a_r_g_e_t program place the mouse  cross	hairs  on  the
       word  QUIT;   the marked control points (including coordinates) will be
       saved.

NNOOTTEESS
       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
       _p_h_o_t_o_._i_n_i_t
	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 accept-
       able.

SSEEEE AALLSSOO
	_i_._o_r_t_h_o_._p_h_o_t_o

       _p_h_o_t_o_._c_a_m_e_r_a

       _p_h_o_t_o_._2_i_m_a_g_e

       _p_h_o_t_o_._i_n_i_t

       _p_h_o_t_o_._r_e_c_t_i_f_y



AAUUTTHHOORR
       Mike Baba,  DBA Systems, Inc.

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_1_1_/_2_7 _0_9_:_1_4_:_1_1 _$



GRASS 5.0						      photo.2target(1)
