enable in-R georeferencing

[EhrmannS]

https://www.esri.com/esri-news/arcuser/spring-2018/understanding-raster-georeferencing

[EhrmannS]

http://www.qgistutorials.com/en/docs/georeferencing_basics.html

[mdsumner]

Hey cool package! For this issue you might be interested in https://github.com/hypertidy/affinething which is for the simple two-point case. The main problem I have is how to make the workflow sensible in an R context?

For the multiple-point cases I was considering using VRT in GDAL via the sf/stars package - but it's a case I very rarely use myself.

[EhrmannS]

To be honest, I haven't put that much thought into the technical implementation. I will study what you did already and perhaps we can develop that further together.

I did prepare a more convenient workflow by enabling zooming in visualise() (via setting a smaller reference window for plotting) and wrote the function gt_locate() for sampling point information. What stopped you to implement a case with more than two points?

[mdsumner]

Just that I don't need it, but I'm interested to help open up the techniques in R