Global motion tracking

[wpd-mlb]

I check the code and found use_motion=False. So how does Global motion tracking work to separate static and dynamic objects?

[YuxueYang1204]

Thanks for the question! To enable it, you need to:

1. Set use_motion=True when calling the reconstructor.
2. Configure the relevant parameters (dynamic_threshold, enable_global_motion_tracking and dynamic_threshold2) in Reconstructor.

The two-stage separation is implemented in GaussianSplatRenderer._classify_gaussians:

1. Stage 1 — Instantaneous velocity separation: Gaussians with velocity magnitude below dynamic_threshold are classified as static. The rest are dynamic.
2. Stage 2 — Global motion tracking (when enable_global_motion_tracking=True): For each static Gaussian, its center is projected onto all frames to sample the velocity at the corresponding pixel. A visibility check (projected_depth ≤ sampled_depth + occlusion_threshold) filters occluded projections. If the visibility-weighted maximum velocity across all frames exceeds dynamic_threshold2, the Gaussian is reclassified as dynamic. This catches objects that appear static in some frames but move in others.

Since the feed-forward reconstruction usually applies coordinate normalization during training, velocity magnitudes can vary significantly across different inputs. As a result, dynamic_threshold and dynamic_threshold2 need to be tuned per-data. We therefore leave global motion tracking off by default but keep the code available for community reference and experimentation.

[wpd-mlb]

Thank you for your reply. I will try