docs/train: document --missing-printspace=project

docs/train.md

@@ -271,6 +271,11 @@ eynollah-training generate-gt pagexml2label \
   -doi "dir of output cropped images"
 ```
 
+Also, note that it can be detrimental to layout training if there are visible segments which
+the annotation does not account for (and thus the model must learn to ignore). So if the images
+are not cropped, the `-ps` _should_ be used. If a PAGE XML file is missing `PrintSpace` (or `Border`)
+annotations, use `-mps` to either `skip` these or `project` (i.e. crop from existing segments).
+
 ## Train a model
 
 ### classification

src/eynollah/training/gt_gen_utils.py

@@ -724,7 +724,11 @@ def get_images_of_ground_truth(
                 print(gt_list[index], "has no Border or PrintSpace - projecting hull of segments")
                 bboxes = list(map(bbox_from_points, coords))
                 left, top, right, bottom = zip(*bboxes)
-                ps_bbox = [min(left), min(top), max(right), max(bottom)]
+                left = max(0, min(left) - 5)
+                top = max(0, min(top) - 5)
+                right = min(x_len, max(right) + 5)
+                bottom = min(y_len, max(bottom) + 5)
+                ps_bbox = [left, top, right, bottom]
             else:
                 print(gt_list[index], "has no Border or PrintSpace - using full page")
                 ps_bbox = [0, 0, None, None]