OCR page-rotation transforms¶

Scanned pages can be rotated before OCR runs. OpenMed exposes an explicit, local-only transform for carrying page-space points, OCR boxes, and source-span references into the rotated page coordinate system.

Coordinates use a top-left origin. A page of width W and height H has the closed outer bounds 0 <= x <= W and 0 <= y <= H; OCR boxes must have positive area and remain within those bounds. Rotation values are clockwise quarter turns only: 0, 90, 180, or 270. A 90° or 270° turn swaps the output width and height.

from openmed.multimodal import PageTransform, transform_bbox, transform_point

transform = PageTransform(page_size=(1000, 800), rotation=90)
point = transform.point((120, 80))
box = transform.bbox((120, 80, 360, 180))

assert point == (720, 120)
assert box == (620, 120, 720, 360)
assert transform.inverse().bbox(box) == (120, 80, 360, 180)

# The functional form is equivalent:
assert transform_point((120, 80), (1000, 800), 90) == point
assert transform_bbox((120, 80, 360, 180), (1000, 800), 90) == box

transform_ocr_result() returns a new OcrResult with the same word text, confidence, page indexes, metadata, and input order; only each word's bounding box changes. Call to_layout() on the transformed result when its new geometry should drive a fresh deterministic reading-order reconstruction. transform_document() similarly preserves text offsets, pages, and span metadata while transforming source bounding boxes.

Malformed dimensions, missing or conflicting rotation, unsupported orientation, inverted boxes, non-finite coordinates, and out-of-bounds geometry raise validation errors. Inputs are rejected rather than clipped so a transform cannot silently change source provenance. Error messages contain stable field names and reason codes, not coordinates, OCR text, or source references.

Collections are bounded to 4,096 words or spans per call. Coordinate and page dimension iterators consume at most the required count plus one; partial or multiple coordinate representations and nested coordinate mappings are rejected. Typed geometry is revalidated at transform boundaries. Conversion and iterator failures do not retain raw exception context. Preserved document text and metadata remain sensitive caller data; transformed records are not de-identified reports.