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docs/convex_decomposition_spec.md

@@ -101,6 +101,42 @@ num_faces
 
 Use `logs/parts_summary.csv` to find parts that are too small, too large, or unexpectedly complex before using them as collision geometry.
 
+### Decomposition granularity controls
+
+CoACD does not directly support a target physical bbox size such as "each part should be about 5 cm". Part size is controlled indirectly through decomposition granularity parameters:
+
+```text
+--threshold              Lower value -> stricter convex approximation -> usually more/smaller parts.
+--max-convex-hull        Caps the number of convex hulls. Lower cap -> fewer/larger parts.
+--no-merge               Disables hull merge. Usually keeps more/smaller parts.
+--mcts-max-depth         Higher value allows deeper recursive splitting.
+--mcts-nodes
+--mcts-iterations        More search can find finer/better splits, with higher runtime.
+--preprocess-resolution
+--resolution             Higher values preserve more geometric detail before decomposition.
+--max-ch-vertex          Controls complexity of each convex hull, not physical size directly.
+```
+
+Practical presets:
+
+```bash
+# Coarser collision: fewer/larger parts, faster simulation
+python scripts/run_convex_decomposition.py <raw_asset_dir> \
+  --mesh <mesh.obj> \
+  --threshold 0.08 \
+  --max-convex-hull 8
+
+# Finer collision: more/smaller parts, more accurate but heavier
+python scripts/run_convex_decomposition.py <raw_asset_dir> \
+  --mesh <mesh.obj> \
+  --threshold 0.02 \
+  --max-convex-hull 32 \
+  --no-merge \
+  --mcts-max-depth 4
+```
+
+After generation, inspect `logs/parts_summary.csv` to decide whether the resulting part sizes are acceptable for the target task.
+
 ### `metadata.yaml`
 
 Minimum fields: