[GRASS-user] Problems running g.gui.gcp

[Moritz Lennert]

On 23/10/15 10:56, Johannes Radinger wrote:
>
>
> On Fri, Oct 23, 2015 at 10:17 AM, Moritz Lennert
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>
>     On 22/10/15 16:25, Johannes Radinger wrote:
>
>         Dear GRASS users,
>
>         Today I wanted to try the georectification tool g.gui.gcp in
>         GRASS 7 for
>         the first time. I was basically following the description on the
>         GRASS
>         wiki (https://grasswiki.osgeo.org/wiki/Georeferencing). In
>         particular, I
>         have a photograph from my camera with known reference points which I
>         load into an unprojected XY location. My target location should
>         also be
>         a XY location as the picture is taken from a "virtual" coordinate
>         system. Inside my target XY-location I try to open g.gui.gcp and
>         select
>         raster, and the location and mapset where my photograph is
>         stored. When
>         I want to click next I get following error/message: "You must
>         select a
>         valid location and mapset in order to continue" and I can't
>         proceed with
>         the rectification. Just this GUI message appears, no
>         error/warning in
>         the grass console etc. I am puzzled how to interpret that? What
>         is wrong
>         with the location/mapset? The mapset I've selected is existing
>         (I can
>         select it from the dropdown menu). I tried to select any other
>         location/mapset but receive always the same message.
>
>
>
>     Georectification is for georeferencing to a projected system. It
>     does not make sense to georeference to an XY-location.
>
>     I see two options for you:
>
>     - Import you image directely into the target region and use r.region
>     to adjust its boundary coordinates
>     - Define your own projection system to fit your needs.
>
>
> So far as I understand georectification and orthorectification in
> particular is to rectify a picture/photo/image based on spatially
> defined ground control points which might not be done by just adjusting
> the boundary coordinates. BTW I also tried the European LAEA coordinate
> system (EPSG 3035) as a target location which is not working either here
> in my machine/setup (same message as already mentioned). Here
> (https://www.dropbox.com/s/snjzd8eu7b8115k/2015-10-22%2015.26.30.jpg?dl=0)
> you can find a a photo (*.jpg) which is an "areal" photo with known 3d
> coordinates for the single points (ground control points). I think this
> example clarifies and illustrates what I intend to do and why the target
> system can also be a XY location in my opinion. A rectification of this
> image should make the lines of the grid more or less parallel. Or do I
> get something completely wrong?

Actually, I was wrong: I don't get any complaint trying to use g.gui.gcp 
to georectify from XY to XY. So there seems to be an issue with your XY 
locations.

Have you tried recreating the locations from scratch ?

Moritz