[GRASSLIST:5906] Re: Scanned images - how to assign coordinates for the first time

[Eric G. Miller]

On Fri, Mar 28, 2003 at 10:29:55PM -0800, John Doucette wrote:
> I seem to be having a conceptual problem with Grass and images.  I
> would like to bring a scanned image into Grass and to assign
> coordinates to the image and then probably save it as a geotiff or
> geojpg.  I thought i.rectify would be the ticket but after trying to
> do so and reading the manual pages I now think that i.rectify is only
> for use with an already rectified image and actually seems to be used
> to transform an already rectified image rather than to assign
> coordinate for the first time.  So how does one put coordinates on a
> scanned image the first time?  Can this be done in Grass or do I have
> to go out and get a multi-hundred/thousand dollar program to assign
> coordinates to a scanned map that doesn't have coordinates assigned
> yet?

i.rectify is exactly the tool.  There's an old image processing tutorial
on the GRASS websites that is still mostly accurate regarding various
procedures.  Actually locating the registration points is handled by
other tools (i.vpoints, etc...).  Registration points are merely a cross
walk (Pixel(X,Y) maps to Coordinate(E,N)) and can be written in a text
editor!

-- 
echo ">gra.fcw at 2ztr< eryyvZ .T pveR" | rot13 | reverse