Spatial-MLLM: Boosting MLLM Capabilities in Visual-based Spatial
  Intelligence
Recent advancements in Multimodal Large Language Models (MLLMs) have
significantly enhanced performance on 2D visual tasks. However, improving their
spatial intelligence remains a challenge. Existing 3D MLLMs always rely on
additional 3D or 2.5D data to incorporate spatial awareness, restricting their
utility in scenarios with only 2D inputs, such as images or videos. In this
paper, we present Spatial-MLLM, a novel framework for visual-based spatial
reasoning from purely 2D observations. Unlike conventional video MLLMs which
rely on CLIP-based visual encoders optimized for semantic understanding, our
key insight is to unleash the strong structure prior from the feed-forward
visual geometry foundation model. Specifically, we propose a dual-encoder
architecture: a pretrained 2D visual encoder to extract semantic features, and
a spatial encoder-initialized from the backbone of the visual geometry model-to
extract 3D structure features. A connector then integrates both features into
unified visual tokens for enhanced spatial understanding. Furthermore, we
propose a space-aware frame sampling strategy at inference time, which selects
the spatially informative frames of a video sequence, ensuring that even under
limited token length, the model focuses on frames critical for spatial
reasoning. Beyond architecture improvements, we construct the Spatial-MLLM-120k
dataset and train the model on it using supervised fine-tuning and GRPO.
Extensive experiments on various real-world datasets demonstrate that our
spatial-MLLM achieves state-of-the-art performance in a wide range of
visual-based spatial understanding and reasoning tasks. Project page:
https://diankun-wu.github.io/Spatial-MLLM/.
68391565d762b7c617b1ba81
Diankun Wu
68391565d762b7c617b1ba82
Fangfu Liu
68391565d762b7c617b1ba83
Yi-Hsin Hung
68391565d762b7c617b1ba84
Yueqi Duan
Spatial-MLLM: Boosting MLLM Capabilities in Visual-based Spatial
  Intelligence
Recent advancements in Multimodal Large Language Models (MLLMs) have
significantly enhanced performance on 2D visual tasks. However, improving their
spatial intelligence remains a challenge. Existing 3D MLLMs always rely on
additional 3D or 2.5D data to incorporate spatial awareness, restricting their
utility in scenarios with only 2D inputs, such as images or videos. In this
paper, we present Spatial-MLLM, a novel framework for visual-based spatial
reasoning from purely 2D observations. Unlike conventional video MLLMs which
rely on CLIP-based visual encoders optimized for semantic understanding, our
key insight is to unleash the strong structure prior from the feed-forward
visual geometry foundation model. Specifically, we propose a dual-encoder
architecture: a pretrained 2D visual encoder to extract semantic features, and
a spatial encoder-initialized from the backbone of the visual geometry model-to
extract 3D structure features. A connector then integrates both features into
unified visual tokens for enhanced spatial understanding. Furthermore, we
propose a space-aware frame sampling strategy at inference time, which selects
the spatially informative frames of a video sequence, ensuring that even under
limited token length, the model focuses on frames critical for spatial
reasoning. Beyond architecture improvements, we construct the Spatial-MLLM-120k
dataset and train the model on it using supervised fine-tuning and GRPO.
Extensive experiments on various real-world datasets demonstrate that our
spatial-MLLM achieves state-of-the-art performance in a wide range of
visual-based spatial understanding and reasoning tasks. Project page:
https://diankun-wu.github.io/Spatial-MLLM/.
Spatial-MLLM improves spatial reasoning in multimodal large language models using a dual-encoder architecture with pretrained 2D and 3D structure encoders, achieving state-of-the-art performance on visual spatial tasks.
spatial-mllm dual-encoder architecture visual geometry foundation model CLIP-based visual encoders semantic features 3D structure features unified visual tokens space-aware frame sampling supervised fine-tuning GRPO spatial understanding spatial reasoning