Ground4D: Spatially-Grounded Feedforward 4D Reconstruction for Unstructured Off-Road Scenes

TL;DR

Ground4D introduces a spatially-grounded, pose-free 4D reconstruction framework that improves off-road scene modeling by resolving temporal conflicts through localized conditioning and auxiliary geometric cues.

Contribution

It proposes voxel-grounded temporal Gaussian aggregation and surface normal cues to enhance 4D reconstruction quality in unstructured off-road scenes.

Findings

Outperforms existing feedforward methods in reconstruction quality.

Generalizes zero-shot to unseen off-road domains.

Demonstrates effectiveness on ORAD-3D and RELLIS-3D datasets.

Abstract

Feedforward Gaussian Splatting has recently emerged as an efficient paradigm for 4D reconstruction in autonomous driving. However, in unstructured off-road scenes, its performance degrades due to high-frequency geometry, ego-motion jitter, and increased non-rigid dynamics. These factors introduce conflicting Gaussian observations across timestamps, leading to either over-smoothed renderings or structural artifacts. To address this issue, we propose Ground4D, a spatially-grounded 4D feedforward framework for pose-free off-road reconstruction. The key idea is to resolve temporal conflicts through spatially localized conditioning. Specifically, we introduce voxel-grounded temporal Gaussian aggregation, which partitions the canonical Gaussian space into spatial voxels and performs query-conditioned temporal attention within each voxel. Intra-voxel softmax normalization ensures that temporal selectivity and spatial occupancy become mutually reinforcing rather than conflicting. We furthermore introduce surface normal cues as auxiliary geometric guidance to regularize the geometry of Gaussian primitives. Extensive experiments on ORAD-3D and RELLIS-3D demonstrate that Ground4D consistently outperforms existing feedforward methods in reconstruction quality and generalizes zero-shot to unseen off-road domains. Project page and code:https://github.com/wsnbws/Ground4D.