Add Ground Control Points support

[paulinus]

There should be an option to use GCP while reconstructing. This should be used when aligning the reconstruction and during bundle adjustment.

[btchouston]

Please @paulinus can you tell me when is gcp used inside the reconstruction ?
Is it absolutely necessary for images to have exif data ?

[YanNoun]

Ground control points supports can be found here : https://www.opensfm.org/docs/using.html#ground-control-points.

@btchouston regarding your questions :

• GCP are used through the SfM reconstruction process during bundle adjustment.
• No necessarily, but it will definitely helps and makes the difference between a bad or average reconstruction and a very good one.