Reference for ultralytics/models/yolo/obb/val.py

def eval_json(self, stats):
    """Evaluates YOLO output in JSON format and returns performance statistics."""
    if self.args.save_json and self.is_dota and len(self.jdict):
        import json
        import re
        from collections import defaultdict

        pred_json = self.save_dir / "predictions.json"  # predictions
        pred_txt = self.save_dir / "predictions_txt"  # predictions
        pred_txt.mkdir(parents=True, exist_ok=True)
        data = json.load(open(pred_json))
        # Save split results
        LOGGER.info(f"Saving predictions with DOTA format to {pred_txt}...")
        for d in data:
            image_id = d["image_id"]
            score = d["score"]
            classname = self.names[d["category_id"] - 1].replace(" ", "-")
            p = d["poly"]

            with open(f'{pred_txt / f"Task1_{classname}"}.txt', "a") as f:
                f.writelines(f"{image_id} {score} {p[0]} {p[1]} {p[2]} {p[3]} {p[4]} {p[5]} {p[6]} {p[7]}\n")
        # Save merged results, this could result slightly lower map than using official merging script,
        # because of the probiou calculation.
        pred_merged_txt = self.save_dir / "predictions_merged_txt"  # predictions
        pred_merged_txt.mkdir(parents=True, exist_ok=True)
        merged_results = defaultdict(list)
        LOGGER.info(f"Saving merged predictions with DOTA format to {pred_merged_txt}...")
        for d in data:
            image_id = d["image_id"].split("__")[0]
            pattern = re.compile(r"\d+___\d+")
            x, y = (int(c) for c in re.findall(pattern, d["image_id"])[0].split("___"))
            bbox, score, cls = d["rbox"], d["score"], d["category_id"] - 1
            bbox[0] += x
            bbox[1] += y
            bbox.extend([score, cls])
            merged_results[image_id].append(bbox)
        for image_id, bbox in merged_results.items():
            bbox = torch.tensor(bbox)
            max_wh = torch.max(bbox[:, :2]).item() * 2
            c = bbox[:, 6:7] * max_wh  # classes
            scores = bbox[:, 5]  # scores
            b = bbox[:, :5].clone()
            b[:, :2] += c
            # 0.3 could get results close to the ones from official merging script, even slightly better.
            i = ops.nms_rotated(b, scores, 0.3)
            bbox = bbox[i]

            b = ops.xywhr2xyxyxyxy(bbox[:, :5]).view(-1, 8)
            for x in torch.cat([b, bbox[:, 5:7]], dim=-1).tolist():
                classname = self.names[int(x[-1])].replace(" ", "-")
                p = [round(i, 3) for i in x[:-2]]  # poly
                score = round(x[-2], 3)

                with open(f'{pred_merged_txt / f"Task1_{classname}"}.txt', "a") as f:
                    f.writelines(f"{image_id} {score} {p[0]} {p[1]} {p[2]} {p[3]} {p[4]} {p[5]} {p[6]} {p[7]}\n")

    return stats

def init_metrics(self, model):
    """Initialize evaluation metrics for YOLO."""
    super().init_metrics(model)
    val = self.data.get(self.args.split, "")  # validation path
    self.is_dota = isinstance(val, str) and "DOTA" in val  # is COCO

def plot_predictions(self, batch, preds, ni):
    """Plots predicted bounding boxes on input images and saves the result."""
    plot_images(
        batch["img"],
        *output_to_rotated_target(preds, max_det=self.args.max_det),
        paths=batch["im_file"],
        fname=self.save_dir / f"val_batch{ni}_pred.jpg",
        names=self.names,
        on_plot=self.on_plot,
    )  # pred

def postprocess(self, preds):
    """Apply Non-maximum suppression to prediction outputs."""
    return ops.non_max_suppression(
        preds,
        self.args.conf,
        self.args.iou,
        labels=self.lb,
        nc=self.nc,
        multi_label=True,
        agnostic=self.args.single_cls or self.args.agnostic_nms,
        max_det=self.args.max_det,
        rotated=True,
    )

def pred_to_json(self, predn, filename):
    """Serialize YOLO predictions to COCO json format."""
    stem = Path(filename).stem
    image_id = int(stem) if stem.isnumeric() else stem
    rbox = torch.cat([predn[:, :4], predn[:, -1:]], dim=-1)
    poly = ops.xywhr2xyxyxyxy(rbox).view(-1, 8)
    for i, (r, b) in enumerate(zip(rbox.tolist(), poly.tolist())):
        self.jdict.append(
            {
                "image_id": image_id,
                "category_id": self.class_map[int(predn[i, 5].item())],
                "score": round(predn[i, 4].item(), 5),
                "rbox": [round(x, 3) for x in r],
                "poly": [round(x, 3) for x in b],
            }
        )

def save_one_txt(self, predn, save_conf, shape, file):
    """Save YOLO detections to a txt file in normalized coordinates in a specific format."""
    import numpy as np

    from ultralytics.engine.results import Results

    rboxes = torch.cat([predn[:, :4], predn[:, -1:]], dim=-1)
    # xywh, r, conf, cls
    obb = torch.cat([rboxes, predn[:, 4:6]], dim=-1)
    Results(
        np.zeros((shape[0], shape[1]), dtype=np.uint8),
        path=None,
        names=self.names,
        obb=obb,
    ).save_txt(file, save_conf=save_conf)