[GRASSLIST:2671] Re: i.points and composite images

[Paul Kelly]

On Tue, 17 Feb 2004, Kirk R. Wythers wrote:

> I am trying to rectify a series of scanned color images. The images
> were read into an xy location with r.in.gdal, Then the individual rgb
> bands were recombined with r.composite (for simplicities sake). I ran
> i.target to assign each group to the target location (a utm location).
> I was going to remove the individual rgb images (with g.mremove)  and
> rectify the composite image only, however, upon running i.points, I
> don't see the composite image as a selection option (only the rgb bands
> are present).
>
> Is this a strong hint to not remove the rgb bands until after the
> rectification process is complete?

r.in.gdal automatically creates an imagery group and adds the three bands
to it. You should run i.group to add the composite image as well. All 4
images should be in the same group as they cover the same area. You can
mark the points on one and then rectify them all simultaneously. Probably
you already know this.

Really what you should do is use the composite image as a backdrop for
digitising the points in i.points and then rectify the 3 bands. You should
keep them because you are losing information when you combine them.

Paul