object-ID alignment mismatch between the public caption JSON files and the instance IDs produced by the official ScanNet++ toolbox preprocessing #9

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1. cy94 commented on Mar 31, 2026

   

   cy94

   on Mar 31, 2026

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   Hi, the instance IDs should be the same as in the released data. Are you using the latest v2 version of the ScanNet++ data? And is the issue only in the validation set?
2. zhaoyibo0422-code commented on Mar 31, 2026

   

   zhaoyibo0422-code

   on Mar 31, 2026

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   Thanks for the quick reply.

   Yes, I am using the latest public ScanNet++ v2 release and the official toolbox pipeline:

   • data_root: /mnt/Datasets/scannetpp/data
   • labels_path: /mnt/Datasets/scannetpp/metadata/semantic_benchmark/top100.txt
   • instance_labels_path: /mnt/Datasets/scannetpp/metadata/semantic_benchmark/top100_instance.txt
   • mapping_file: /mnt/Datasets/scannetpp/metadata/semantic_benchmark/map_benchmark.csv
   • list_path: /mnt/Datasets/scannetpp/splits/nvs_sem_train_val.txt

   I generated the full .pth with:
   python -m semantic.prep.prepare_training_data semantic/configs/prepare_training_data.yml

   Then I ran sample_pth.py and converted to Mask3D .npy.

   From the toolbox code, vtx_instance_anno_id is assigned from segGroups[].objectId, and I verified:

   • full .pth and sampled .pth have the same instance IDs
   • sampled .pth and final .npy also have the same instance IDs

   So the mismatch seems to be between the public ExCap3D caption JSON keys and segGroups[].objectId in the public v2 ScanNet++ data.

   Concrete example: scene 286b55a2bf

   • in scans/segments_anno.json:
     • toilet -> objectId=51
     • sink -> objectId=50
     • soap dispenser -> objectId=49
     • door -> objectId=63
     • cabinet -> objectId=72
   • but in the public ExCap3D caption JSON for the same scene, the corresponding captions are keyed as:
     • 13 -> toilet caption
     • 14 -> sink caption
     • 15 -> soap dispenser caption
     • 32 -> door caption
     • 33 -> cabinet caption

   So at least for this scene, the caption keys do not match objectId.

   I first noticed it on val, but it does not seem val-only. Across the public train+val caption release, I found mixed scene-level key patterns rather than a single consistent mapping.

   Could you clarify whether the public caption JSON keys are expected to match segGroups[].objectId, or whether they correspond to another scene-local ID (e.g. segGroup index / instance_ndx)? If a remapping step is required for the public release, could you share the official procedure?Duplicate of #
3. zhaoyibo0422-code commented on Apr 1, 2026

   

   zhaoyibo0422-code

   on Apr 1, 2026

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   From my checks, the caption JSON keys do not behave like a single global ID field from the raw public ScanNet++ v2 annotations. Across scenes, they look mixed: some match objectId, some match segGroup index, and some match segGroup index + 1.

   So I suspect “the released data” in your comment may refer to the released processed ExCap3D/Mask3D data rather than raw ScanNet++ v2 + self-generated preprocessing.

   Could you clarify which exact instance-id field in the released processed data is expected to match the public caption JSON keys?

   • segGroups[].objectId / vtx_instance_anno_id
   • segGroup index / vtx_instance_labels
   • or another released remapped scene-local instance id
4. SpeedyGonzales949 commented on May 8, 2026

   

   SpeedyGonzales949

   on May 8, 2026

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   I have the same issue. e.g.: Ids also do not match for scene ef69d58016.