  We present NeRF-Det, a novel method for indoor 3D detection with posed RGB
images as input. Unlike existing indoor 3D detection methods that struggle to
model scene geometry, our method makes novel use of NeRF in an end-to-end
manner to explicitly estimate 3D geometry, thereby improving 3D detection
performance. Specifically, to avoid the significant extra latency associated
with per-scene optimization of NeRF, we introduce sufficient geometry priors to
enhance the generalizability of NeRF-MLP. Furthermore, we subtly connect the
detection and NeRF branches through a shared MLP, enabling an efficient
adaptation of NeRF to detection and yielding geometry-aware volumetric
representations for 3D detection. Our method outperforms state-of-the-arts by
3.9 mAP and 3.1 mAP on the ScanNet and ARKITScenes benchmarks, respectively. We
provide extensive analysis to shed light on how NeRF-Det works. As a result of
our joint-training design, NeRF-Det is able to generalize well to unseen scenes
for object detection, view synthesis, and depth estimation tasks without
requiring per-scene optimization. Code is available at
\url{https://github.com/facebookresearch/NeRF-Det}.
