[GRASSLIST:5949] Image registration

[John Doucette]

Dear all:

I am learning to use Grass for geologic projects.  I have made significant
progress in this direction but still have far to go.

My immediate need is to bring scanned images of geologic lithology and
structural overlays into Grass and then to digitize lines and polygons over
them.  My searches of the net and manual pages have lead me to believe that
this is possible.  My field mapping was done on mylar overlays and I have a
total of about 34 8-1/2x11" overlays covering my field area.

I have learned how to bring the overlays into grass as raster images using
r.in.tiff after setting the regions north, south, east, and west to the
pixel dimensions of the images.  Then I know how to group images together
using i.group.  I am somewhat comfortable with using i.target to indicate
the destinations region that the image will be projected into and can set up
points using i.points.

My questions are:

1. If I am using mylar overlays on a utm grid is it then necessary to mark
10-12 points on each overlay sheet before I try to use i.rectify or is there
a simpler way using a lesser number of points?

2. If I rectify say 34 images can/should  I then merge them somehow withing
Grass?

3. Is this even a method I should try to use?  Would I be better off
digitizing lines and polygons in a cad or gis program and importing dxf or
shape files?

Any help would be appreciated.

John