more geometry heuristics for validate/repair

[bertsky]

We should have heuristics to check for

• polygon containment (overlapping regions, word outside line etc.)
• artifacts from annotation like point or line-like regions
• lines with (way) too much whitespace (bad cropping, or bad segmentation)
• probably even: missing @orientation

Originally posted by @kba in OCR-D/assets#28 (comment)

[bertsky]

BTW, shapely.geometry.polygon.Polygon has very nice API for the first 2 tasks, including contains() and area().

The third could be achieved with ad-hoc binarization and some simple Numpy statistics like count_nonzero() (i.e. pixel-counting), or nonzero() followed by amin() and amax() to get non-white bounds (i.e. area-counting).

And orientation checking could be done in a similar way like deskewing (i.e. entropy based), but with some kind of confidence measure.

[bertsky]

A good reference for additional checks are the validation error classes in Aletheia, p. 118/119.

[kba]

c.f. https://github.com/OCR-D/ocrd_evaluate_segmentation

[bertsky]

c.f. https://github.com/OCR-D/ocrd_evaluate_segmentation

now renamed to https://github.com/OCR-D/ocrd_segment (there will be more processors)

[kba]

https://github.com/OCR-D/ocrd_segment is a better place for this.

[bertsky]

Moved the original issue from core here to have a better reminder of what is left to do.

Out of the original list, we are still somewhere in the first item I think. (We do not yet check whether elements are properly contained within their parents' outline.)

[bertsky]

(We do not yet check whether elements are properly contained within their parents' outline.)

And the question then is, how does repair look like in that case? Shrink the element's polygon or xtend the parent's polygon?