[GRASS-user] repair regularly compressed or stretched images

GRASS GRASS user
1

Dear list,

I have hundreds of automatically scanned and manually geocoded maps and at first
sight they fit perfectly at the borders where the 4 control points where set.
But within they are sometimes compressed or stretched regularly. I mean it
occurs only from east to west (column by column) following certain rules
(north to south is fine). So I guess there was a scanner problem from the
beginning.

Now, I would like to compress and stretch all these maps again to fix the
scanner problems somehow. Does anybody has an idea, if this is possible with
GRASS? I am not keen to scan and geocode all images again, so maybe someone
has solved a similar problem already or has a hint?

thanks a lot,
Otto

2

Otto Dassau wrote:

I have hundreds of automatically scanned and manually geocoded maps and at first
sight they fit perfectly at the borders where the 4 control points where set.
But within they are sometimes compressed or stretched regularly. I mean it
occurs only from east to west (column by column) following certain rules
(north to south is fine). So I guess there was a scanner problem from the
beginning.

Now, I would like to compress and stretch all these maps again to fix the
scanner problems somehow. Does anybody has an idea, if this is possible with
GRASS? I am not keen to scan and geocode all images again, so maybe someone
has solved a similar problem already or has a hint?

What is the nature of the distortion? If it's just a constant scale
factor, you can change a map's bounds with r.region. Otherwise, you
can use i.rectify.

--
Glynn Clements <glynn@gclements.plus.com>