Exact upstream SC-GS hard deformation activation failed on the controlled procedural scene. The primary mechanism was the opacity reset scheduled at the same update as hard deformation activation. The optimizer step then added a secondary deformation overshoot.
This is a negative upstream result. It is not relabeled as a successful unmodified SC-GS baseline.
Machine source:
/mnt/d/Track4D-GS-outputs/activation_audit/activation_abcd_run2_node/summary.json.
The audit restored the accepted update-2,999 checkpoint in a fresh process and
used camera r_000, time 0.0, the restored RNG state, and the same active SH
degree for all renders.
| State | Meaning | PSNR | SSIM | alpha mean | visible |
|---|---|---|---|---|---|
| A | pre-activation detached forward | 14.6476 | 0.57042 | 0.99372 | 278,636 |
| B | attached full-deformation forward, pre-backward | 14.6476 | 0.57042 | 0.99372 | 278,636 |
| C4 | post-backward and post-densification, pre-reset | 13.9804 | 0.51011 | 0.99309 | 289,011 |
| C5 | post-opacity-reset, pre-optimizer | 8.8589 | 0.12350 | 0.13983 | 289,011 |
| D | post-optimizer | 8.9064 | 0.11209 | 0.25577 | 289,660 |
A and B were tensor-identical for RGB, alpha, canonical positions, translation, rotation, scaling, and transformed positions. B and the post-backward state were also tensor-identical. Therefore neither attaching autograd nor backward changed the forward state.
Densification caused a moderate quality change. The C4-to-C5 opacity reset
changed no geometry or deformation outputs, but changed RGB by up to 1.67157
and alpha by up to 0.99003; this is the primary discontinuity. The C5-to-D
optimizer step then changed translation/transformed position by up to
1.45827, rotation output by 0.06750, and scaling output by 0.06569.
At the update-3,000 boundary the pinned source:
- attaches the deformation network and control nodes after the warm-up;
- activates translation, quaternion rotation, and additive scaling together;
- applies the local-frame control-node warp before raster projection;
- executes Gaussian densification and the scheduled opacity reset;
- keeps deformation-network and control-node parameters in their existing optimizer groups and learning-rate schedules;
- does not perform node densification at this boundary.
The failure was therefore classified as a coincident maintenance discontinuity with a secondary optimizer contribution, not as a camera or coordinate error.
The selected named protocol is Stabilized SC-GS, distinct from exact upstream SC-GS:
- a 1,000-update smoothstep coefficient;
- translation
alpha * t_predicted; - identity-to-predicted quaternion SLERP for rotation;
- scaling interpolated in the additive representation consumed by SC-GS;
- only the opacity reset coincident with activation is skipped;
- original optimizer learning rates;
- no coordinate changes, position clamps, motion truncation, LR reduction, or gradient clipping.
The 500-update bridge failed after three focused engineering repairs: a stale reference, zero-angle SLERP NaNs, and then non-finite rotation at update 3,200. The 1,000-update bridge passed 300 full-deformation updates and was extended to 500 full-deformation updates.
Accepted checkpoint:
/mnt/d/Track4D-GS-outputs/stabilized_scgs/stabilized_scgs_attempt2_full_extension200_node/checkpoints/main_update_04499.pt
- SHA-256:
9e5f63cd643463183fa5f5e725ee4f6ff38331a3b8ef82db28f89a179fbf8216 - size: 387,945,298 bytes
- Gaussians: 444,687
- control nodes: 128
- peak reserved VRAM: 4,649,385,984 bytes
- alpha: exactly 1
- fully activated updates: 500
- fresh-process restore and one additional update: passed