rectifiying image

[Jim Hinthorne]

>I have several maps that have been given to me and inputed
>to the computer via scanner.  The image comes in great
>using r.in.gif, but alas no coordinate system.
>
>No surprise there.  How can I attach a coordinate system
>to the image, if I have several know point on the map?
>
>If any other suggestions can be made to get these maps
>into my grass system, it would be appreciated.
>Thanks for any help.
>
>Kym M. Lenkus
>DAVIDSON LABORATORY
>Stevens Institute of Technology
>
Get the GRASS Image Processing Tutorial from the moon server, and pay close 
attention to the section on rectification/georeferencing.  If you have a lot 
of control points, i.rectify2 does a very nice job, otherwise use i.rectify.

The general sequence of events is:
1. start grass4.1 and create or verify that you have a mapset in the 
location with the desired final coordinates.  exit grass.
2.  start grass4.1 and create or use a location with an x-y coordinate system.
3.  import the images into the cell directory in this x-y mapset.
4.  build header files using r.support and be sure the images display ok.
5.  run i.group and put your "co-registered" bands into a group.
6.  run i.target and specify the destination location and mapset--must be on 
same disk as x-y location.
7.  run i.points and specify the control points (this can take much time and 
reading of manual pages and tutorial.
8.  run i.rectify or i.rectify2
9.  exit grass and reenter grass4.1 in the destination location and mapset 
and check the quality of the registration.

cheers.
Jim Hinthorne                        Voice: 509-963-2826
GIS/Geology                         FAX:   509-963-1047
Central Washington Univ.       E-mail: geol1 at cwu.edu