No subject

Joyce Anne Nagle nagle at
Tue Jan 12 13:46:35 EST 1993

We are trying to orthorectify an image with i.ortho.rectify,
and have found the following problems:

1.  When we leave the X,Y, Z, kappa, phi, omega blank, and let the program solve
for them, the resulting image has a scale about twice as large as it should be
when overlaid on the DEM that we are rectifying to.

2.  When we put in approximate X,Y, Z values, the scale looks more nearly
correct, but it apparently takes these values as the truth rather than as 
approximations. (when we give it slightly different X,Y,Z values, the image is
translated exactly the same amount as the difference)

3. In all cases, the resulting image remains square, and it should really
be more trapezoidal, since one side of the photo is approximately 2500feet
higher elevatiion than the other.

Also does anyone know what algorithms are used in this module? Or have
references to this?

Are there any experts out there who would like to give us advice?


Emily Bryant
Dept. of Earth Sciences
Dartmouth College
emily.bryant at

Joyce A. Nagle
U.S. Army Cold Regions Research and Engineering Laboratory (CRREL)
Remote Sensing and GIS Center        email:  nagle at
72 Lyme Road                         phone:  (603) 646-4161 / 4100
Hanover, NH  03755-1290              fax:    (603) 646-4278

More information about the grass-user mailing list