Scanner resolution and cell size

[Michel Wurtz - ENGEES/CEREG]

Rich Shepard wrote:
> What do other folks do when using scanned aerial photos to define cell size?

You can only have an "idea" of an average cell size when scanning
aerial photos, because scale varies with elevation, camera position
and orientation, etc.

The first thing to do is rectifying the image. But you need
some information about the fligh and the camera (at least focal
length, ...), a DEM and the coordinate of some points you can
identify on your image for georeferencing.  If the terrain is flat,
it's simpler (known points is all you need) and i.rectify will do
the job.  If you need a DEM, use i.ortho.photo.  The cell size
after one of this tool is used will be the one set in your current
region.

-- 
Michel Wurtz    ENGEES - CEREG
                1, quai Koch - BP 1039, F-67070 STRASBOURG cedex
                Tel: +33 03.88.24.82.45  Fax: +33 03.88.37.04.97