usd_models/scripts/usd_cleaner/Readme.md

# USD models cleaner

Finds the USD models under `assets/usd_models` that no scene actually uses, and
deletes them. Pure standard library — no Isaac Sim, no `pxr`, no pip installs.

Two scripts, run in order:

| File | What it does |
| --- | --- |
| `usd_models_cleaner.py` | Seeds from `assets/scenes/*.json`, follows references *inside* the USD files transitively, writes the list to JSON. Read-only. |
| `usd_models_delete.py` | Takes that JSON and deletes the listed files, then removes folders left without any USD. Destructive. |

Both resolve paths against the repo root, so they work from any directory.

## 1. Build the list

```bash
python3 scripts/usd_cleaner/usd_models_cleaner.py --unused
```

Writes **`unused_usds.json`** next to the script — every USD file under
`assets/usd_models` that no scene references. That is the delete list.

Without `--unused` it writes **`used_usds.json`** instead: the models that *are*
referenced. Useful as a sanity check.

| Flag | Effect |
| --- | --- |
| `--unused` | Invert: list what is NOT reachable (the delete list) |
| `--aggressive` | Drop the sibling-directory guard (riskier, deletes more) |
| `--no_follow` | Scene JSONs only — **unsafe**, reproduces the old broken behaviour |
| `--out PATH` | Write somewhere else (a bare name lands in this folder) |
| `--no_out` | Print only, write no file |
| `--verbose` | Annotate each path with the scenes referencing it |
| `--scenes_dir` / `--models_dir` | Point at different directories |

## 2. Preview

```bash
python3 scripts/usd_cleaner/usd_models_delete.py unused_usds.json --dry-run
```

Prints every file and folder that would go, plus the total freed. Touches nothing.
**Always run this first.**

## 3. Delete

```bash
python3 scripts/usd_cleaner/usd_models_delete.py unused_usds.json
```

Prints a summary and asks `[y/N]` before removing anything.

| Flag | Effect |
| --- | --- |
| `--dry-run` | Preview only |
| `--yes` | Skip the confirmation prompt |
| `--keep_empty_dirs` | Delete the files but leave USD-less folders in place |
| `--models_dir` | Confine deletion to a different directory |

## Rules it follows

- **Folder removal.** A folder is removed only if it *held* a USD file and now
  holds none. A folder that never held one — `textures/`, `material/` — belongs
  to its parent model and is left alone, so surviving models keep their assets.
- **Protected folders.** `.git`, `.svn`, `.hg`, `__pycache__` and any dotted
  folder are never swept. Without this the "no USD inside" rule would delete
  `assets/usd_models/.git` wholesale.
- **Containment.** Deletion cannot leave `--models_dir`. A `../` in the list
  aborts the run instead of escaping.
- **Only `.usd`, `.usda`, `.usdc`, `.usdz`** count as models. A `.png` or a
  backup file whose *name* contains `.usd` is not a model and is not counted.

## How references are followed

A scene names a wrapper; the geometry and joints usually live elsewhere. The
cleaner therefore starts at the scene paths and walks outward:

1. **`.usda` text** — parsed for `@asset/path@` (and the `@@@path@@@` form),
   resolved relative to the file holding the reference. Reliable.
2. **`.usdc` binary** — the token table is compressed, so printable strings are
   mined and kept only when they resolve to a file that exists. Best-effort.
3. **Companion folder** — `X.usd` beside a folder `X/` pulls in that whole
   folder. This is the convention these assets use and it is what catches what
   the binary scan misses.
4. **Sibling directories** — a reachable *binary* USD also protects the
   directories next to it, since its real references are unreadable.
   `kitchen_background.usd` keeps `localized/` this way. `--aggressive` turns
   this off.

Every step is repeated transitively until nothing new is reached.

## Why this matters

An earlier version scanned scene JSONs only. It deleted
`model_dishwasher_v2/resource/v_0/link_default_0.usda` — never named by any
scene, but the file holding the dishwasher's articulation. Isaac Sim then failed
with:

    RuntimeError: Failed to find an articulation when resolving
    '/World/envs/env_0/model_dishwasher'

`--no_follow` reproduces that behaviour for comparison. Do not delete with it.

## Before you delete

The binary side is a heuristic, not a parser. Only `pxr` (via
`/isaac-sim/python.sh`) can resolve `.usdc` references with certainty. Treat the
list as a strong suggestion, not proof.

Scene JSONs may also not be the only referrer — task configs or code can name a
model directly.

`assets/usd_models` is a git repo, which is the real safety net: after deleting,
`git status` shows every removal and `git reset --hard HEAD` restores them.
Load a scene before committing the deletions.

## Current numbers

158 paths declared by scenes expand to **264 reachable USD files**; 652 are
unreachable. Scene-JSON-only scanning would have kept just 158 and deleted 729 —
the 106-file difference is what broke the dishwasher.