OMR Search: Add class for creating ngrams of information extracted from MEI

app/public/cantusdata/helpers/mei_processing/bounding_box_utils.py

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+"""
+Module containing utilities for the manipulation of bounding boxes 
+obtained from MEI files.
+"""
+
+from typing import List, Tuple, Dict
+import json
+from collections import defaultdict
+from .mei_parsing_types import Zone
+
+
+def combine_bounding_boxes_single_system(bounding_boxes: List[Zone]) -> Zone:
+    """
+    Combing a list of bounding boxes contained within a single system into
+    one bounding box with no rotation.
+
+    NOTE: This function does not handle cases where any of the bounding boxes
+    has a rotation != 0. The rotation is currently ignored, but Issue #834 has
+    been created to rectify this.
+
+    :param bounding_boxes: A list of bounding boxes. See mei_parsing_types.Zone for
+        the structure of a bounding box.
+    :return: A single bounding box that contains the contents of all the given
+        bounding boxes and has rotation = 0.
+    """
+    # Collect the upper-left ("ulx", "uly") and lower-right ("lrx", "lry") vertex
+    # coordinates of each bounding box
+    ulx_list: List[int] = []
+    uly_list: List[int] = []
+    lrx_list: List[int] = []
+    lry_list: List[int] = []
+    for box in bounding_boxes:
+        ulx_list.append(box["coordinates"][0])
+        uly_list.append(box["coordinates"][1])
+        lrx_list.append(box["coordinates"][2])
+        lry_list.append(box["coordinates"][3])
+    comb_ulx = min(ulx_list)
+    comb_uly = min(uly_list)
+    comb_lrx = max(lrx_list)
+    comb_lry = max(lry_list)
+
+    return {"coordinates": (comb_ulx, comb_uly, comb_lrx, comb_lry), "rotate": 0}
+
+
+def combine_bounding_boxes(bounding_boxes: List[Tuple[Zone, int]]) -> List[Zone]:
+    """
+    Combine bounding boxes that may cross multiple systems. This function
+    takes a list of bounding boxes and the system number that each box
+    belongs to, and returns a list of bounding boxes, one for each system.
+
+    :param bounding_boxes: A list of 2-tuples, each containing (1) a bounding
+        box and (2) the system number that the bounding box belongs to.
+    :return: A list of bounding boxes, one for each system.
+    """
+    # Create a dictionary to store the bounding boxes for each system
+    system_boxes: Dict[int, List[Zone]] = defaultdict(list)
+    for box, system in bounding_boxes:
+        system_boxes[system].append(box)
+
+    # Combine the bounding boxes for each system, in system order
+    combined_boxes = []
+    for _, boxes in sorted(system_boxes.items()):
+        combined_boxes.append(combine_bounding_boxes_single_system(boxes))
+
+    return combined_boxes
+
+
+def stringify_bounding_boxes(bounding_boxes: List[Zone]) -> str:
+    """
+    Convert a list of bounding box types to a string for indexing. The
+    string encodes some JSON, an array of objects, each of which
+    represents a bounding box:
+
+        [
+            {"ulx":  , # X-coordinate of upper left corner of box
+            "uly":  , # Y-coordinate of upper left corner of box
+            "width": , # Height of the box
+            "height":  }, # Width of the box
+            ...
+        ]
+
+    :param bounding_box: A list of bounding boxes (Zone type)
+    :return: A string representation of the bounding boxes
+    """
+    bbox_strings: List[Dict[str, int]] = []
+    for box in bounding_boxes:
+        ulx = box["coordinates"][0]
+        uly = box["coordinates"][1]
+        width = box["coordinates"][2] - box["coordinates"][0]  # lrx - ulx
+        height = box["coordinates"][3] - box["coordinates"][1]  # uly - lry
+        bbox_strings.append({"ulx": ulx, "uly": uly, "width": width, "height": height})
+    return json.dumps(bbox_strings)