New postprocess function label_regions

The new function uses the new printspace estimator to classify each
region as either margin or printspace. It is right now implemented as a
volume postprocess method.

src/htrflow_core/utils/geometry.py

@@ -363,3 +363,29 @@ def is_twopage(img, strip_width=0.1, threshold=0.2):
     if np.min(strip) < np.sort(levels)[int(w * threshold)]:
         return middle - half_strip + np.argmin(strip)
     return None
+
+
+class RegionLocation:
+    PRINTSPACE = "printspace"
+    MARGIN_LEFT = "margin_left"
+    MARGIN_RIGHT = "margin_right"
+    MARGIN_TOP = "margin_top"
+    MARGIN_BOTTOM = "margin_bottom"
+
+
+def get_region_location(printspace: Bbox, region: Bbox) -> RegionLocation:
+    """Get location of `region` relative to `printspace`
+
+    The side margins extends to the top and bottom of the page. If the
+    region is located in a corner, it will be assigned to the left or
+    right margin and not the top or bottom margin.
+    """
+    if region.center.x < printspace.xmin:
+        return RegionLocation.MARGIN_LEFT
+    elif region.center.x > printspace.xmax:
+        return RegionLocation.MARGIN_RIGHT
+    elif region.center.y > printspace.ymax:
+        return RegionLocation.MARGIN_TOP
+    elif region.center.y < printspace.ymin:
+        return RegionLocation.MARGIN_BOTTOM
+    return RegionLocation.PRINTSPACE

src/htrflow_core/volume/postprocess.py

@@ -1,5 +1,6 @@
 from copy import deepcopy
 
+from htrflow_core.utils.geometry import estimate_printspace, get_region_location
 from htrflow_core.volume import volume
 
 
@@ -43,3 +44,22 @@ def is_noise(node: volume.BaseDocumentNode, threshold: float = 0.8):
         conf = sum(child.get("text_result").top_score() for child in node) / len(node.children)
         return conf < threshold
     return False
+
+
+def label_regions(volume: volume.Volume, key="region_location"):
+    """Label volume's regions
+
+    Labels each top-level segment of the volume as one of the five
+    region types specified by geometry.RegionLocation. Saves the label
+    in the node's data dictionary under `key`.
+
+    Arguments:
+        volume: Input volume
+        key: Key used to save the region label. Defaults to
+            "region_location".
+    """
+
+    for page in volume:
+        printspace = estimate_printspace(page.image)
+        for node in page:
+            node.add_data(**{key: get_region_location(printspace, node.bbox)})