## NAME

i.rectify3 - An imagery function that rectifies an image by computing a coordinate transformation for each cell (pixel) in the image using the transformation parameters generated by the GRASS program i.points3.
(GRASS Image Processing Program)

## SYNOPSIS

i.rectify3

## DESCRIPTION

i.rectify3 rectifies an image by using the transformation paramters generated by i.points3. Rectification is the process by which the geometry of an image is made planimetric. This is accomplished by mapping (transforming) an image from one coordinate system to another. In i.rectify3, the coefficients computed by i.points3 are used in an equation to convert x,y coordinates to standard map coordinates for each cell in the image. The user can select either a POLYNOMIAL, ORTHO-PHOTO, or LANDSAT-TM transformation using i.points3. The result of i.rectify3 is an image with a standard map coordinate system. Upon completion of the program the rectified image is deposited in a previously targeted GRASS LOCATION_NAME and MAPSET.

The GRASS programs i.target and i.points3 must be run prior to i.rectify3.

The first prompt in the program asks the user for the name of the group containing the raster map layers to be rectified.

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

The user is then asked to select the map layer(s) within the group to be rectified:

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

               spot.1 in demo:.........
               spot.2 in demo:.........
               spot.3 in demo:.........
               spotclass in demo:spotrectify..
               spotreject in demo:.........

           (Enter list by any name to get a list of existing raster files)

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

More than one raster map layer may be rectified at a time. Each raster map layer should have a unique output file name.

Next the user is asked to select one of two geographic region settings:

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

i.rectify3 will only rectify that portion of the image that occurs within the chosen geographic region setting. Only that portion will be relocated in the target data base. It is therefore important to check the current geographic region settings in the target location if choice number one is selected.

## NOTES

The rectification process may take an hour or more depending on the resolution of the image, the number of files, and the size of the geographic region definition.

The rectified (raster) image will be located in the target LOCATION when the program is completed. The original unrectified raster map layers are not modified or removed.

## SEE ALSO

GRASS Tutorial: Image Processing

m.proj, s.proj, s.proj, v.proj, i.group, i.points3, i.rectify, i.target

## AUTHOR

Mike Baba, DBA Systems.

Michael Shapiro, U. S. Army Construction Engineering Research Laboratory wrote the original i.rectify program, from which the new program was developed.

Last changed: $Date: 2002/01/25 05:45:33 $