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Sanmin Kim

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4 papers

2 author rows

ICRA Conference 2025 Conference Paper

CRAB: Camera-Radar Fusion for Reducing Depth Ambiguity in Backward Projection Based View Transformation

In-Jae Lee
Sihwan Hwang
Youngseok Kim 0001
Wonjune Kim
Sanmin Kim
Dongsuk Kum

Recently, camera-radar fusion-based 3D object detection methods in bird's eye view (BEV) have gained attention due to the complementary characteristics and cost-effectiveness of these sensors. Previous approaches using forward projection struggle with sparse BEV feature generation, while those employing backward projection overlook depth ambiguity, leading to false positives. In this paper, to address the aforementioned limitations, we propose a novel camera-radar fusion-based 3D object detection and segmentation model named CRAB (Camera-Radar fusion for reducing depth Ambiguity in Backward projection-based view transformation), using a backward projection that leverages radar to mitigate depth ambiguity. During the view transformation, CRAB aggregates perspective view image context features into BEV queries. It improves depth distinction among queries along the same ray by combining the dense but unreliable depth distribution from images with the sparse yet precise depth information from radar occupancy. We further introduce spatial cross-attention with a feature map containing radar context information to enhance the comprehension of the 3D scene. When evaluated on the nuScenes open dataset, our proposed approach achieves a state-of-the-art performance among backward projection-based camera-radar fusion methods with 62. 4% NDS and 54. 0% mAP in 3D object detection.

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IROS Conference 2025 Conference Paper

REOcc: Camera-Radar Fusion with Radar Feature Enrichment for 3D Occupancy Prediction

Chaehee Song
Sanmin Kim
Hyeonjun Jeong
Juyeb Shin
Joonhee Lim
Dongsuk Kum

Vision-based 3D occupancy prediction has made significant advancements, but its reliance on cameras alone struggles in challenging environments. This limitation has driven the adoption of sensor fusion, among which camera-radar fusion stands out as a promising solution due to their complementary strengths. However, the sparsity and noise of the radar data limits its effectiveness, leading to suboptimal fusion performance. In this paper, we propose REOcc, a novel camera-radar fusion network designed to enrich radar feature representations for 3D occupancy prediction. Our approach introduces two main components, a Radar Densifier and a Radar Amplifier, which refine radar features by integrating spatial and contextual information, effectively enhancing spatial density and quality. Extensive experiments on the Occ3D-nuScenes benchmark demonstrate that REOcc achieves significant performance gains over the camera-only baseline model, particularly in dynamic object classes. These results underscore REOcc’s capability to mitigate the sparsity and noise of the radar data. Consequently, radar complements camera data more effectively, unlocking the full potential of camera-radar fusion for robust and reliable 3D occupancy prediction.

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AAAI Conference 2023 Conference Paper

CRAFT: Camera-Radar 3D Object Detection with Spatio-Contextual Fusion Transformer

Youngseok Kim
Sanmin Kim
Jun Won Choi
Dongsuk Kum

Camera and radar sensors have significant advantages in cost, reliability, and maintenance compared to LiDAR. Existing fusion methods often fuse the outputs of single modalities at the result-level, called the late fusion strategy. This can benefit from using off-the-shelf single sensor detection algorithms, but late fusion cannot fully exploit the complementary properties of sensors, thus having limited performance despite the huge potential of camera-radar fusion. Here we propose a novel proposal-level early fusion approach that effectively exploits both spatial and contextual properties of camera and radar for 3D object detection. Our fusion framework first associates image proposal with radar points in the polar coordinate system to efficiently handle the discrepancy between the coordinate system and spatial properties. Using this as a first stage, following consecutive cross-attention based feature fusion layers adaptively exchange spatio-contextual information between camera and radar, leading to a robust and attentive fusion. Our camera-radar fusion approach achieves the state-of-the-art 41.1% mAP and 52.3% NDS on the nuScenes test set, which is 8.7 and 10.8 points higher than the camera-only baseline, as well as yielding competitive performance on the LiDAR method.

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ICRA Conference 2023 Conference Paper

Joint Semi-Supervised and Active Learning via 3D Consistency for 3D Object Detection

Sihwan Hwang
Sanmin Kim
Youngseok Kim 0001
Dongsuk Kum

Autonomous driving powered by deep learning requires large-scale, high-quality training data from diverse driving environments to operate effectively worldwide. However, collecting and annotating such data is costly and time-consuming. To address this challenge, active learning methods have been explored to select the most informative data samples for training. Nevertheless, most existing methods focus on 2D tasks and do not fully exploit the value of unlabeled data. In this paper, we propose a semi-supervised active learning approach for 3D object detection tasks that leverages the potential of collected data and reduces annotation costs. Our method considers the 3D consistency of bounding box predictions in both semi-supervised and active learning processes, thereby improving the performance of point cloud-based 3D object detection models. Our framework specifically utilizes self-supervision to decrease bounding box uncertainties. Moreover, it selects objects that are either occluded or distant and still exhibit high uncertainty for annotation even after semi-supervised training has decreased their uncertainty. Experiments on the KITTI dataset demonstrate that our semi-supervised active learning approach selects objects with high measurement uncertainties and enhances the model's ability to detect occluded objects. Our approach improves the baseline by more than 60% (+17. 12 mAP) when using only 1500 annotated frames.

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