[GRASS-user] Auto-detection of GCP for rectifying image

[Moritz Lennert]

On 06/10/16 11:59, Johannes Radinger wrote:
> Hi GRASS users!
>
> I have an image of a small object (e.g. photograph of blue square
> 15x5cm) which I want to automatically georeference. In addition, the
> image contains 6 points where I know the exact coordinates, i.e. these
> points can be use as ground control points (GCP) for rectifying the
> image. This is basically a experimental setup, and I could use different
> colors or shapes for the GCP; the image itself will then be rather a
> photograph of a fish on a white background than a blue square; I just
> want to test with a simpler setup before.
>
> However, as I want to automatize the step of rectifying/georeferencing I
> am looking for a way to autodetect these six points in the image. I am
> thinking of tools like pattern/face recognition that are able to
> autodetect objects (e.g. eyes, points etc.) and extract their position
> (coordinates) within that image. I assume these coordinates together
> with their "true" position could then be used for rectifying the picture
> using e.g. i.rectify.
>
> Has anyone done this or a similar exercise before and can recommend
> tools and approaches to auto-detect GCP from an image?

I've never used it, but there's i.points.auto in the addons:

https://grass.osgeo.org/grass70/manuals/addons/i.points.auto.html

Moritz