Restrict Annotations to Image Bounds

[hennels]

Problem:

Currently, annotations can be placed outside the image. Annotations outside the image can cause problems in downstream processes that assume annotations to be inside the given image and cannot be accurate outside the image when there is no visual context there.

Proposed Solution:

Restricting annotations to the image alone would make annotating slightly harder as having the slack to click outside an image is much easier than following the image border exactly. To keep the annotations inside the image it would help to just clamp/clip any click outside the image to the closest point inside the image. That way the annotator can still use the outside the tile space as slack to help follow the edge of the image to keep annotating the same level of difficulty as today.

Just like the snap to edge that exists for polylines, but for points and polygons you would probably have to just snap to the nearest point inside the image.