masks.py 文件源码

def mask_to_poly(mask, xymax, epsilon=2, min_area=1., threshold=0.5):
    # __author__ = Konstantin Lopuhin
    # https://www.kaggle.com/lopuhin/dstl-satellite-imagery-feature-detection/full-pipeline-demo-poly-pixels-ml-poly

    # first, find contours with cv2: it's much faster than shapely
    contours, hierarchy = cv2.findContours(((mask >= threshold) * 255).astype(np.uint8), cv2.RETR_CCOMP, cv2.CHAIN_APPROX_TC89_KCOS)

    # create approximate contours to have reasonable submission size
    approx_contours = [cv2.approxPolyDP(cnt, epsilon, True) for cnt in contours]

    if not contours:
        return MultiPolygon()

    # now messy stuff to associate parent and child contours
    cnt_children = defaultdict(list)
    child_contours = set()
    assert hierarchy.shape[0] == 1

    # http://docs.opencv.org/3.1.0/d9/d8b/tutorial_py_contours_hierarchy.html
    for idx, (_, _, _, parent_idx) in enumerate(hierarchy[0]):
        if parent_idx != -1:
            child_contours.add(idx)
            cnt_children[parent_idx].append(approx_contours[idx])

    # create actual polygons filtering by area (removes artifacts)
    all_polygons = []
    for idx, cnt in enumerate(approx_contours):
        if idx not in child_contours and cv2.contourArea(cnt) >= min_area:
            assert cnt.shape[1] == 1
            poly = Polygon(
                shell=cnt[:, 0, :],
                holes=[c[:, 0, :] for c in cnt_children.get(idx, [])
                       if cv2.contourArea(c) >= min_area])
            all_polygons.append(poly)

    # approximating polygons might have created invalid ones, fix them
    all_polygons = MultiPolygon(all_polygons).buffer(0)

    # Sometimes buffer() converts a simple Multipolygon to just a Polygon,
    # need to keep it a Multi throughout
    if all_polygons.type == 'Polygon':
        all_polygons = MultiPolygon([all_polygons])

    return convert_poly_to_geo_coords(all_polygons, mask.shape, xymax)