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

[Johannes Radinger]

On Fri, Oct 23, 2015 at 10:17 AM, Moritz Lennert <
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?

/Johannes



>
>
> Moritz
>
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