i.rectify(1)	       Grass User's Manual	     i.rectify(1)



NNAAMMEE
       ii..rreeccttiiffyy   - rectifies an image by computing a coordinate
       transformation for each pixel in the image  based  on  the
       control points created by _i_._p_o_i_n_t_s or _i_._v_p_o_i_n_t_s.
       _(_G_R_A_S_S _I_m_a_g_e _P_r_o_c_e_s_s_i_n_g _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       ii..rreeccttiiffyy

DDEESSCCRRIIPPTTIIOONN
       _i_._r_e_c_t_i_f_y  uses	the control points identified in _i_._p_o_i_n_t_s
       or _i_._v_p_o_i_n_t_s to calculate a transformation matrix based on
       a   first, second, or third order polynomial and then con-
       verts x,y cell coordinates to standard map coordinates for
       each  pixel  in	the  image.   The result is a planimetric
       image with a transformed coordinate system (i.e.,  a  dif-
       ferent coordinate system than before it was rectified).


       _i_._p_o_i_n_t_s  or  _i_._v_p_o_i_n_t_s	must be run before _i_._r_e_c_t_i_f_y, and
       both programs are required to rectify an image.	An  image
       must be rectified before it can reside in a standard coor-
       dinate LOCATION, and therefore be analyzed with the  other
       map layers in the standard coordinate LOCATION.	Upon com-
       pletion of _i_._r_e_c_t_i_f_y, the rectified image is deposited  in
       the target standard coordinate LOCATION.  This LOCATION is
       selected using _i_._t_a_r_g_e_t.

PPrrooggrraamm PPrroommppttss
       The first prompt in the program asks for the name  of  the
       group containing the files to be rectified.

	    Enter the group containing files to be rectified
	    Enter 'list' for a list of existing imagery groups
	    Enter 'list -f' for a verbose listing
	    Hit RETURN to cancel request
	    >

       This  is  the  same  imagery  group  that  was selected in
       _i_._p_o_i_n_t_s or _i_._v_p_o_i_n_t_s and the group that contains the cell
       files  with  the  marked  points  and their associated map
       coordinates.  You  are  then  asked  to	select	the  cell
       file(s) within the group to be rectified:

       Please  select  the file(s) to rectify by naming an output
       file

	      spot1.1 in mapsetname	 .............
	      spot1.2 in mapsetname	 .............
	      spot1.3 in mapsetname	 .............
	      spotclass1 in mapsetname	 spotrectify1.

	      spotreject1 in mapsetname  .............

       (enter list by any name to get a  list  of  existing  cell
       files)

       AFTER COMPLETING ALL ANSWERS, HIT <ESC> TO CONTINUE
		  (OR<Ctrl-C> TO CANCEL)

       More  than one cell file may be rectified at a time.  Each
       cell file should be given a unique output file name.


       Next, you are asked to select one of two windows regions:

	 Please select one of the following options
	 1.  Use the current window in the target location
	 2.  Determine the smallest window which covers the image
	 >

       The  _i_._r_e_c_t_i_f_y  program	will only rectify that portion of
       the image or cell file that occurs within the chosen  win-
       dow region, and only that portion of the cell file will be
       relocated in the target database.  It is important  there-
       fore,  to  check  the  current mapset window in the target
       LOCATION if choice number one is selected.


       If you are rectifying a file with plans	to  patch  it  to
       another	file  using  the  GRASS  program  _r_._p_a_t_c_h, choose
       option number one, the current window in the target  loca-
       tion.   This  window,  however, must be the default window
       for the target LOCATION.  When a file being  rectified  is
       smaller	than the default window in which it is being rec-
       tified, zeros are added to the rectified  file.	 Patching
       files of the same size that contain 0/non-zero data, elim-
       inates the possibility  of  a  no-data  line  the  patched
       result.	This is because, when the images are patched, the
       zeros in the image are "covered" with non-zero pixel  val-
       ues.   When rectifying files that are going to be patched,
       rectify all of the files using the same default window.


       By selecting the 1st ORDER option, the user may select the
       order of transformation desired:

       Select  order  of  transformation    1st Order	2nd Order
       3rd Order

       The program will immediately recalculate the RMSE and  the
       number of points required.

   LLiinneeaarr aaffffiinnee ttrraannssffoorrmmaattiioonn ((11sstt oorrddeerr ttrraannssffoorrmmaattiioonn))
       x' = ax + by +c y' = Ax + Bt +C

       The a,b,c,A,B,C are determined by least squares regression
       based on the control points entered.  This  transformation
       applies	scaling,  translation  and rotation.  It is NOT a
       general purpose rubber-sheeting,  nor  is  it  ortho-photo
       rectification  using  a	DEM, not second order polynomial,
       etc.  It can be used if (1) you have geometrically correct
       images,	and  (2)  the terrain or camera distortion effect
       can be ignored.

   PPoollyynnoommiiaall TTrraannssffoorrmmaattiioonn MMaattrriixx ((22nndd,,  33dd  oorrddeerr  ttrraannssffoorrmmaa--
       ttiioonn))
       The ANALYZE function has been changed to support calculat-
       ing the registration coefficients using a  first,  second,
       or  third order transformation matrix.  The number of con-
       trol points required for a selected order  of  transforma-
       tion (represented by n) is ((n + 1) * (n + 2) / 2)

       or  3,  6, and 10 respectively. It is strongly recommended
       that one or more additional points be identified to  allow
       for an overly- determined transformation calculation which
       will generate the Root Mean Square (RMS) error values  for
       each  included  point.	The  RMS error values for all the
       included control points are immediately recalculated  when
       the user selects a different transformation order from the
       menu bar.  The polynomial equations are performed using	a
       modified Gaussian elimination method.

   PPrrooggrraamm EExxeeccuuttiioonn
       _i_._r_e_c_t_i_f_y  will	run  in  the background and notify you by
       mail when it is finished.


       Note:  The rectified image or rectified cell files will be
       located	in  the  target LOCATION when the program is com-
       pleted.	The original unrectified files are  not  modified
       or removed.


       Note:  In  interactive mode it is possible to define a new
       file name for the target images. This is  (currently)  not
       provided in command line mode.

NNOOTTEESS
       _i_._r_e_c_t_i_f_y  uses	nearest  neighbor  resampling  during the
       transformation choosing the actual pixel that has its cen-
       tre  nearest to the point location in the image. Advantage
       of this method is that the pixel brightness of  the  image
       is  kept as _i_._r_e_c_t_i_f_y rearranges the geometry of the image
       pixels.

SSEEEE AALLSSOO
       _G_R_A_S_S _T_u_t_o_r_i_a_l_: _I_m_a_g_e _P_r_o_c_e_s_s_i_n_g



       _m_._p_r_o_j_,	_s_._p_r_o_j_,  _s_._p_r_o_j_,   _v_._p_r_o_j_,   _i_._g_r_o_u_p_,	_i_._p_o_i_n_t_s_,
       _i_._p_o_i_n_t_s_3_, _i_._v_p_o_i_n_t_s_, _i_._r_e_c_t_i_f_y_3_, _i_._t_a_r_g_e_t


AAUUTTHHOORR
       William	R.  Enslin, Michigan State University, Center for
       Remote Sensing


       Modified for GRASS 5.0 by:

       Luca Palmeri (palmeri@ux1.unipd.it)

       Bill Hughes

       Pierre de Mouveaux (pmx@audiovu.com)
       CMD mode by Bob Covill

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_3 _$



GRASS 5.0					     i.rectify(1)
