Describe the feature or enhancement you're looking for
It's often easy to find two GCPs, but finding a third can be quite challenging. Reasons this can happen include:
- The map is along a waterfront
- The map depicts an area that's almost completely changed (example: page 44 of Brooklyn, NY 1939 Vol 1).
If you assume that the x- and y-scale of the image are the same, and that there's no skew, then two GCPs are sufficient to define a model. This is a four parameter model, rather than the full six parameter affine model.
So far as I can tell, there's no direct support for this type of model in the IIIF georeference extension. A workaround would be to have a "generate third point" button that would create a new GCP at a location that forms a right triangle with the two existing GCPs. This would get mapped to the point on the map that assumes the same scale in both dimensions and zero skew.
Of course, it's better to find a real third or fourth point. But in a pinch, this would be better than guessing. Maybe the feature could be buried behind a menu to discourage its use.
If this request is linked to a problem, please describe.
(see above)
Describe alternatives you've considered
I usually guess about what features in the water (like a pier) might exist and correspond, and see what looks reasonable.
Additional context
Add any other context or screenshots about the feature request here.
Describe the feature or enhancement you're looking for
It's often easy to find two GCPs, but finding a third can be quite challenging. Reasons this can happen include:
If you assume that the x- and y-scale of the image are the same, and that there's no skew, then two GCPs are sufficient to define a model. This is a four parameter model, rather than the full six parameter affine model.
So far as I can tell, there's no direct support for this type of model in the IIIF georeference extension. A workaround would be to have a "generate third point" button that would create a new GCP at a location that forms a right triangle with the two existing GCPs. This would get mapped to the point on the map that assumes the same scale in both dimensions and zero skew.
Of course, it's better to find a real third or fourth point. But in a pinch, this would be better than guessing. Maybe the feature could be buried behind a menu to discourage its use.
If this request is linked to a problem, please describe.
(see above)
Describe alternatives you've considered
I usually guess about what features in the water (like a pier) might exist and correspond, and see what looks reasonable.
Additional context
Add any other context or screenshots about the feature request here.