3D Architect: An Automated Approach to Three-Dimensional Modeling

Single-view 3D reconstruction is a challenging task in computer vision due to information missing from the single input image. Generative model-based approaches can produce plausible 3D objects from a single image, thanks to data-driven priors learnt from rich and large-scale datasets. However, plausible generation does not guarantee fidelity to the geometry and appearance of the particular input object. Inspired by object perception in human vision, we propose OPERA, a framework that guides multi-view diffusion sampling with pretrained perception models through lightweight alignment modules. These modules are trained independently while both the generative and perception models remain frozen, allowing multiple signals to be combined at inference without joint fusion training. We evaluate OPERA on two single-view 3D reconstruction baselines using subsets of Google Scanned Objects and OmniObject3D. On the primary baseline, combined guidance reduces mean Chamfer Distance by 30.4% and 24.8%, respectively, relative to unguided reconstruction. We also compare our method with recent image-to-3D models. We provide in-depth analyses of the design choices and their effects across datasets and backbones. Our project page is at https://opera-3d.github.io/.

LiDAR-based 3D object detectors typically rely on proposal heads with hand-crafted components like anchor assignment and non-maximum suppression (NMS), complicating training and limiting extensibility. We present AutoReg3D, an autoregressive 3D detector that casts detection as sequence generation. Given point-cloud features, AutoReg3D emits objects in a range-causal (near-to-far) order and encodes each object as a short, discrete-token sequence consisting of its center, size, orientation, velocity, and class. This near-to-far ordering mirrors LiDAR geometry--near objects occlude far ones but not vice versa--enabling straightforward teacher forcing during training and autoregressive decoding at test time. AutoReg3D is compatible across diverse point-cloud or backbones and attains competitive nuScenes performance without anchors or NMS. Beyond parity, the sequential formulation unlocks language-model advances for 3D perception, including GRPO-style reinforcement learning for task-aligned objectives. These results position autoregressive decoding as a viable, flexible alternative for LiDAR-based detection and open a path to importing modern sequence-modeling tools into 3D perception.

Single-image-to-3D generative models can now produce high-quality geometry, yet conditioning on a single view inevitably introduces ambiguity about unseen regions. Multi-view conditioning can reduce this ambiguity, but existing methods either require fixed canonical viewpoints or rely on external reconstruction modules that impose heavy training costs and limit generation quality. We observe that pretrained single-view models already possess strong 2D-to-3D grounding that can be reused for multi-view conditioning. However, a closer analysis reveals that their conditioning mechanism entangles orientation control with geometry transfer, two functions that conflict when images from different viewpoints are naively combined. Based on this analysis, we propose ROAR-3D, a lightweight method that upgrades a pretrained single-view model to accept an arbitrary number of unposed images. A token-wise view router assigns each 3D latent token to its most relevant view, implicitly establishing 2D-to-3D correspondences without explicit pose input. A dual-stream attention design preserves the pretrained primary-view behavior while routing auxiliary views through a separate path dedicated to geometric enrichment. An orientation perturbation strategy ensures the auxiliary path learns orientation-independent geometry transfer. These components introduce minimal trainable parameters and add negligible inference overhead relative to the single-view baseline. ROAR-3D achieves state-of-the-art multi-view 3D generation quality and supports test-time view scaling from 1 to 12+ views with consistent improvements.