Multi-Level Neural Scene Graphs for Dynamic Urban Environments

Overview

What?

We estimate the radiance field of large-scale dynamic areas from multiple vehicle captures under varying environmental conditions.

Why?

Previous works in this domain are either restricted to static environments, do not scale to more than a single short video, or struggle to separately represent dynamic object instances.

How?

1. We present a decomposable multi-level neural scene graph representation that scales to dynamic urban environments with thousands of images from dozens of sequences with hundreds of fast-moving objects. Each dynamic object $v_o$ is associated with a sequence node $v_s^t$ and time $t$. The sequence nodes are registered in a common world frame at the root node $v_r$ through the vehicle poses $\mathbf{P}_s^t$, while the dynamic objects are localized w.r.t. the sequence node with pose $\xi^t$. Each camera $c$ is associated with an ego-vehicle position, \ie node $v_s^t$, through the extrinsic calibration $\mathbf{T}_c$. The sequence and object nodes hold latent codes $\omega$ that condition the radiance field, synthesizing novel views in various conditions with distinct dynamic objects.

2. To enable efficient training and rendering, we develop a fast composite ray sampling and rendering scheme. If a ray intersects with an object $v_o$, we sample from both an efficient proposal network $\sigma_\text{prop}$ and a dynamic radiance field $\psi$. We condition each with the latents $\omega$ of the respective nodes. The PDF along the ray is a mixture of all node densities that intersect with the ray. The transmittance $U$ drops at the first surface intersection (tree) where further samples will concentrate.

3. To test our approach in urban driving scenarios, we introduce a new, novel view synthesis benchmark. We choose two urban geographic areas, one residential (left) and one downtown (right). We extract sequences with heterogeneous capturing conditions from these areas using Argoverse 2 as data source. We improve the initial GPS-based alignment with an offline ICP procedure.

Comparison to state-of-the-art

Our approach outperforms prior art by a significant margin on both established and our proposed benchmark while being faster in training and rendering. We provide qualitative illustrations below. Note that all results are rendered from a single model trained on multiple sequences.

BibTeX

@InProceedings{ml-nsg,
    author    = {Fischer, Tobias and Porzi, Lorenzo, and Rota Bul\`{o}, Samuel and Pollefeys, Marc and Kontschieder, Peter},
    title     = {Multi-Level Neural Scene Graphs for Dynamic Urban Environments},
    booktitle = {Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR)},
    year      = {2024}
}