Use when converting any sensor dataset into NVIDIA NCore V4 format (and feeding it to NuRec or a robotics-to-sim "r2s" pipeline). Covers ingesting raw cameras, LiDARs, radars, IMUs, depth or stereo into V4 sequences; authoring a new converter from the template; adapting PAI / Waymo / PandaSet / NuScenes to V4; handling non-AV rigs (mono+depth, mono+lidar, stereo, multi-stereo, RGB-D, COLMAP / SfM, ROS2 bag); and diagnosing a broken converter against `validate.py`. Do NOT use to train reconstructions (use `nre`) or to extract per-object 3D assets (use `asset-harvester`). Trigger keywords: ncore, ncore v4, convert, ingest, zarr, itar, nurec, waymo, pandaset, nuscenes, pai, hyperion, colmap, scannetpp, stereo, multi-stereo, mono+depth, mono+lidar, kitti, sfm, camera, lidar, radar, imu, cuboid, poses, intrinsics, ego mask, ros2, rosbag, mcap, realsense, zed, rgb-d, r2s, robotics, sam2.
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Use when converting any sensor dataset into NVIDIA NCore V4 format (and feeding it to NuRec or a robotics-to-sim "r2s" pipeline). Covers ingesting raw cameras, LiDARs, radars, IMUs, depth or stereo into V4 sequences; authoring a new converter from the template; adapting PAI / Waymo / PandaSet / NuScenes to V4; handling non-AV rigs (mono+depth, mono+lidar, stereo, multi-stereo, RGB-D, COLMAP / SfM, ROS2 bag); and diagnosing a broken converter against `validate.py`. Do NOT use to train reconstructions (use `nre`) or to extract per-object 3D assets (use `asset-harvester`). Trigger keywords: ncore, ncore v4, convert, ingest, zarr, itar, nurec, waymo, pandaset, nuscenes, pai, hyperion, colmap, scannetpp, stereo, multi-stereo, mono+depth, mono+lidar, kitti, sfm, camera, lidar, radar, imu, cuboid, poses, intrinsics, ego mask, ros2, rosbag, mcap, realsense, zed, rgb-d, r2s, robotics, sam2.
Convert any sensor recording (cameras, LiDAR, radar, IMU, depth,
stereo, COLMAP/SfM, ROS 2 bag) into a valid NVIDIA NCore V4 store
so it can be consumed by NuRec / Asset Harvester / ncore_vis, or
wired into a robotics-to-sim ("r2s") pipeline. Drive the existing
in-tree converters (PAI, Waymo, COLMAP/ScanNet++) or author a new
converter from ncore_template/.
Use this skill when: the user has raw sensor data (any rig) that
NuRec or Asset Harvester needs to ingest, or when an existing
converter is failing validate.py / producing NuRec data-quality
complaints.
Do NOT use this skill when:
The user is already on V4 and only wants to train or render
(use the nre skill).
The user wants per-object 3D assets from sparse views (use
asset-harvester).
The user only needs to browse / pick an existing NVIDIA dataset
(use physical-ai-datasets).
This skill teaches an agent to take any sensor dataset and produce a valid
NCore V4 store that NuRec / Asset Harvester / ncore_vis will accept. It covers
both driving the existing in-tree converters (PAI, Waymo, COLMAP/ScanNet++)
and writing a new one for unsupported formats (PandaSet, NuScenes, KITTI,
stereo, mono+depth, mono+lidar, custom robotics rigs).
PAI clip on HuggingFace, or a local PAI clip directory
Path A — tools/data_converter/pai:convert (pai-stream-v4 / pai-v4)
Waymo .tfrecord files
Path A — tools/data_converter/waymo:convert (waymo-v4)
COLMAP scene (or ScanNet++ DSLR)
Path A — tools/data_converter/colmap:convert (colmap-v4 / scannetpp-v4)
Mono RGB images, no poses
Path A.5 — run COLMAP first, then colmap-v4
PandaSet, NuScenes, KITTI, Argoverse, custom AV rig
Path B — author from ncore_template/impl/data_converter/example_converter.py
Stereo / mono+depth / mono+lidar / robotics
Path B
Already have parsed numpy/torch arrays in memory
Path B but skip Bazel — use ncore.data.v4 API directly
If a candidate path exists in upstream, prefer it. Hand-rolling a Waymo or
PAI converter on top of the template is wasted work and almost certainly wrong
(rolling-shutter timing, FTheta intrinsics, Waymo camera-frame rotation, etc).
Prerequisites
Linux host with Python ≥ 3.10 and pip.
git for the upstream converter sources.
bazel only if you run the in-tree converters (Path A); pure-Python
in-process writes (ncore.data.v4) need no Bazel.
Disk: budget tens of GB per converted clip; pre-zarr scratch can be
larger than the final .zarr.itar.
HuggingFace token (HF_TOKEN) only if pulling a gated PAI clip.
Verifying secrets safely
Always verify prerequisites with the upstream validate.py or by
running the converter against a tiny test slice; never write ad-hoc
bash that interpolates HF_TOKEN values. The common one-liner
# BAD — leaks the secret to the terminal when the variable is setecho"HF_TOKEN: ${HF_TOKEN:+yes}${HF_TOKEN:-no}"
prints yes<token-value> whenever HF_TOKEN is set, because
${VAR:-no} only falls back to "no" when the variable is empty. Use
a length-only check, which never echoes the value:
# OK — prints "set (N chars)" or "missing", never the valuetest -n "$HF_TOKEN" && echo"HF_TOKEN: set (${#HF_TOKEN} chars)" || echo"HF_TOKEN: missing"
Per-ray unit direction + per-ray µs timestamp + distance(s) + intensity + model_element=(row,col)
LidarSensorComponent
RadarSensor(optional)
Same shape as LiDAR minus intensity / model_element
RadarSensorComponent
Cuboids(optional, recommended)
CuboidTrackObservation list referencing rig / world / sensor frames
CuboidsComponent
Masks
Per-camera dict of {name: PIL.Image} (NuRec requires ego masks)
MasksComponent
PointClouds(optional)
Pre-computed dense or SfM points (e.g. COLMAP sfm_points, depth-derived)
PointCloudsComponent
Frames of reference (these are non-negotiable — wrong frames = silent NuRec failure):
Rig: +X forward, +Y left, +Z up. Origin at the middle of the rear axle on nominal ground for AV, or any natural body-fixed point for non-AV. All extrinsics are T_sensor → rig.
Camera sensor: +X right, +Y down, +Z forward (optical axis). NCore's convention. Waymo (X-fwd) and similar must be rotated before storing extrinsics.
LiDAR model frame: azimuth 0° = +X, 90° = +Y, +Z up. Independent of the raw sensor's native azimuth — you choose how column_azimuths_rad maps physical columns.
World: sequence-local. Re-reference all T_rig_world to the first ego pose so origin is near the vehicle start (raw UTM/ECEF at 10+ km loses precision in float32). Carry the original first pose into T_world_world_global (float64) if you need a global anchor.
Image pixels: u right, v down, origin at the top-left corner of the top-left pixel (so pixel centers are at 0.5, 0.5).
Units: timestamps in µs everywhere, distances in metres, angles in radians.
Some downstream pipelines need metadata beyond the per-component data — carry
it on the sequence's generic_meta_data (passed to
SequenceComponentGroupsWriter(...)):
Stereo pairs — required by stereo-depth modules (Foundation Stereo) and
multi-camera training configs to discover left/right pairings:
Multiple pairs are allowed for surround-stereo rigs.
Source tag — distinguishes real from synthetic data. Renderer-output
shards (NuRec sim) set {"source": "simulation", "model_checkpoint": "..."};
real-sensor shards omit the key or set {"source": "real"}. Downstream
validators key off this to skip "expected vs measured" checks on sim data.
Calibration / egomotion provenance — the example template writes
calibration_type and egomotion_type on the PosesComponent's
generic_meta_data. Use this to track the upstream tool (e.g.
egomotion_type: "cuvslam-stereo" or "kiss-icp" or "vio:orbslam3") so
later modules can pick refinement strategies that match the input quality.
Instructions
Pick one of the two paths below.
Path A if the user's dataset format is already supported in
ncore/tools/data_converter/ (PAI, Waymo, COLMAP/ScanNet++) —
bootstrap the upstream repo and drive the existing binary.
Path B if the format is unsupported (PandaSet, NuScenes, KITTI,
custom rig, robotics bag, …) — copy ncore_template/ next to the
dataset and fill in the four hand-written hooks. The V4 conventions
in the Mental model section above are mandatory; the recipes
further down show typical configurations per rig.
After conversion, always run the Validation & end-to-end NuRec
section below before handing the store to NRE.
Path A — drive an existing in-tree converter
The upstream tools/data_converter/<format> modules are Bazel targets. Build
once, run per dataset.
Bootstrap
git clone --depth 1 https://github.com/NVIDIA/ncore.git
cd ncore
bazel build //tools/data_converter/pai:convert # or waymo, or colmap
Each convert binary takes shared base flags (--root-dir, --output-dir,
--no-cameras, --camera-id, --no-lidars, --lidar-id, --verbose) followed
by a subcommand (pai-v4, pai-stream-v4, waymo-v4, colmap-v4,
scannetpp-v4) with format-specific flags.
Standard sub-flags worth knowing
Flag
Default
Meaning
--store-type {itar,directory}
itar
itar is fastest for NuRec; directory is debuggable
--profile {default,separate-sensors,separate-all}
varies
NuRec wants separate-sensors
--sequence-meta / --no-sequence-meta
enabled
Writes <sequence>.json next to the store — NuRec/ncore_vis need it
--world-global-mode {none,identity,localized}
varies
For NuRec releases that require the world→world_global edge, use identity (or localized to keep a real global anchor)
When to script vs run interactively
For a one-off conversion, the bare bazel run form in each format recipe
below is enough. For repeatable cluster runs, wrap the same two steps
(bazel build then bazel run) inside an OSMO / Slurm / Kubernetes task that
clones NCore at a pinned ref, runs the convert step, and chains the result
into the nre training and aux-data containers (see
nre's Workflow A). The upstream
NVIDIA/ncore repo ships reference
converter targets that you can pin by Git commit for reproducibility.
Path B — author a new converter from the template
The scaffold is intentionally minimal but writes every required component
type with placeholder data. Treat it as a checklist: every # FILL IN is a
correctness gate — none can be skipped.
Scaffold
# Copy the scaffold next to your dataset (run from this skill's folder)cp -r ncore_template /path/to/ncore-myformat
Then rename the package and class (ExampleConverter → MyFormatConverter) and
implement the contract:
Method
Contract
get_sequence_ids(config) -> list[str]
Discover sequence IDs from config.root_dir (or wherever your dataset lives — manifest CSV, HF clip index, ROS bag glob)
from_config(config) -> Converter
One-time setup (load calibration, open dataset index, init shared interpolators). Heavy lifting that all sequences share goes here
Inside convert_sequence the canonical order is Poses → Intrinsics → Masks →
Camera → LiDAR → Radar → Cuboids → finalize. This order is not required by the
writer but it surfaces calibration / pose / timing bugs before you've spent
minutes encoding image bytes.
The skeleton walks each step explicitly and lists every silent-correctness
trap inline — read these before filling them in:
Per-ray LiDAR timestamps and the three data shapes (range image / sensor-frame
XYZ / world-frame XYZ requiring decompensation):
example_converter.py:746-829
The contract (component order, dtype rules, timestamp constraints) is identical.
V4 conventions you must obey
These are the rules that turn into runtime asserts (or worse: silent NuRec
artefacts). Cross-reference the spec before relaxing any of them.
Time
Microseconds, uint64, everywhere.np.uint64, not np.int64.
The sequence interval is half-closed [start, stop). Build it with
HalfClosedInterval.from_start_end(start, end_inclusive) — do not
pre-add 1 to end.
Dynamic poses must exactly span the interval: timestamps[0] == start and
timestamps[-1] == stop - 1. Sensors with timestamps slightly outside this
range are clamped at write time.
Per-sensor frame timestamps are [exposure_start, exposure_end] (cameras) or
[sweep_start, sweep_end] (LiDAR/radar). They must lie within the sequence
interval and the end must be unique within that sensor's writer.
Rolling-shutter cameras: start = trigger + half_shutter,
end = readout_done - half_shutter. Global shutter: start == end is OK.
LiDAR frame_timestamps_us[0] is the sweep start (not midpoint). Per-ray
timestamp_us must lie in [sweep_start, sweep_end]. Treating the dataset's
frame timestamp as the midpoint and subtracting half a sweep duration
introduces a ~50 ms shift on a 10 Hz LiDAR and produces motion-comp blur.
Pose graph
All intermediate pose math is float64. Cast to float32 only as the very
last step before store_dynamic_pose / store_static_pose.
Exception: world → world_global stays float64 (NuRec's
RigTrajectories.T_world_base is float64).
Re-reference dynamic poses to the first ego pose:
poses_f64 = inv(poses_f64[0]) @ poses_f64. Without this, GPS/UTM/ENU at
10+ km loses sub-cm precision once cast to float32.
The pose trajectory must be dense (waypoint spacing < LiDAR sweep
duration, e.g. <50 ms for 10 Hz). Combine every available source: per-camera
per-frame poses, per-LiDAR per-sweep poses, IMU/GPS/odometry. Concatenate,
np.unique by timestamp, sort.
T_camera_rig and T_lidar_rig are float32 (NuRec's transform_poses leaks
input dtype through an internal matmul; float64 here collides with the
float32 trajectory and crashes "Get Lidar Point Clouds" with
RuntimeError: double != float).
LiDAR
Direction vectors are unit-norm, in sensor coordinates, at each ray's
measurement time (not the sweep-start time). Three input shapes:
Polar range image with beam geometry → derive directly from
column_azimuths_rad[col], row_elevations_rad[row],
row_azimuth_offsets_rad[row]. Direction:
(cos(elev)*cos(azi), cos(elev)*sin(azi), sin(elev)).
Sensor-frame XYZ → direction = xyz / |xyz|.
World-frame or ego-compensated XYZ → decompensate with
MotionCompensator.motion_decompensate_points, then normalise.
spinning_direction: nearly all automotive spinning LiDARs (Velodyne,
Hesai, Ouster, Robosense) are "cw". The template defaults to
"ccw" to force the question. Wrong value mirrors Y → Z-flip in NuRec.
row_elevations_rad: non-uniform on every common sensor. Read real
per-beam angles from the sensor calibration. Strictly descending
(highest beam first); reverse if your source is ascending. NCore asserts
np.diff > 0 after projecting through relative_angle.
column_azimuths_rad: must reflect the actual per-column azimuth at
frame start (not a synthetic linspace). NCore validates strict ordering
via relative_angle(azim[0], azim, spinning_direction). If raw
per-column heading is available, use it; otherwise linspace(0, ±2π, N, endpoint=False) is acceptable for "ccw" / "cw" respectively.
row_azimuth_offsets_rad: zero for most sensors; non-zero on Ouster
(beam_azimuth_angles from the HTTP API). Skipping this on Ouster
misaligns LiDAR-to-camera projection.
Per-ray timestamp_us is required for motion compensation; supply real
per-column firing times (typically column-linear across the sweep).
Cuboids
BBox3.centroid is the geometric center. Many AV datasets use
bottom-center → add dim_z / 2 to z. Verify empirically: mean(z) - mean(h)/2
near 0 = geometric center; near mean(h)/2 above ground = bottom-center.
reference_frame_id ∈ {"rig", "world", <sensor_id>}.
reference_frame_timestamp_us and timestamp_us must lie within the
sequence interval.
LabelSource: tag the origin pipeline, not quality. Third-party
dataset labels (Waymo, NuScenes, PandaSet) → EXTERNAL, even if the upstream
is human GT. Use GT_ANNOTATION only when this converter's team owns the
annotation.
Camera
Image bytes stored verbatim (JPEG/PNG); NCore does not re-encode.
Use the model that matches your sensor: OpenCVPinholeCameraModelParameters
(most AV cameras), OpenCVFisheyeCameraModelParameters (Kannala-Brandt
fisheye, e.g. ScanNet++ / GoPro), FThetaCameraModelParameters (NVIDIA
Hyperion / equidistant-radial). Resolution must match the actual image bytes
bit-for-bit.
Map shutter direction by enum name, not integer cast. The five
ShutterType values are ROLLING_TOP_TO_BOTTOM=1, ROLLING_LEFT_TO_RIGHT=2,
ROLLING_BOTTOM_TO_TOP=3, ROLLING_RIGHT_TO_LEFT=4, GLOBAL=5. Build a
source-enum-to-name dict.
Provide ego masks. NuRec's data-quality guide requires binary
ego-vehicle masks per camera. Without them the hood/roof rack leaks into the
reconstruction.
NuRec data-quality minimums
Per the NuRec "Ensure Data Quality" guide, hitting these is the difference
between a clean reconstruction and visible artefacts:
Camera extrinsics: < 0.5° rotation, < 2 cm translation (relative to rig).
Camera intrinsics: < 1 px reprojection error.
Egomotion: < 0.5° / < 2.5 cm consecutive-frame error; trajectory must cover
every sensor frame's start and end timestamp.
Cuboids: < 1° / < 5 cm position / < 5 cm dimension; per-track stable
track_ids.
Original sensor resolution at full FPS, no undistortion / rectification.
Format recipes (AV)
PAI (NVIDIA Physical AI Autonomous Vehicles, HuggingFace)
HF dataset: nvidia/PhysicalAI-Autonomous-Vehicles. License must be accepted
on HF before HF_TOKEN works.
7 cameras (FTheta + Fisheye + Pinhole depending on FOV), 1 top LiDAR
(lidar_top_360fov, spinning, see datasheet for elevations).
Camera intrinsics include shutter_delay_us for per-row rolling-shutter
timestamping, plus optional BivariateWindshieldModelParameters for
windshield refraction.
Discover clip IDs via the clip_index.parquet blob in the HF dataset
(nvidia/PhysicalAI-Autonomous-Vehicles) — the
physical-ai-datasets skill has the
download recipe and toolkit pointers.
Subset by time with --seek-sec / --duration-sec; subset sensors with
--no-lidars / --camera-id (repeatable).
car2sim_6cam sim configs target CARLA sensor names; PAI exports use real
Hyperion IDs — when feeding NRE training, override dataset.camera_ids /
dataset.lidar_ids on the NRE Hydra command line (see
nre Workflow A and references/configuration.md).
Camera intrinsics → OpenCVPinholeCameraModelParameters. Waymo's local
camera frame is +X principal axis; the converter rotates to NCore's
+Z principal axis. If you re-derive extrinsics manually, apply the same
rotation to T_camera_rig.
Multi-return LiDAR (primary + secondary). Stack into the [R, N] distance /
intensity arrays.
PandaSet
No upstream converter — author with Path B. PandaSet (Hesai +
Scale-AI-labelled) ships JSON metadata with each sequence.
Sensor inventory:
6 cameras (front_camera, front_left_camera, front_right_camera,
back_camera, left_camera, right_camera) — pinhole, global shutter.
Intrinsics in meta/intrinsics/<id>.json.
2 LiDARs:
front_lidar: Hesai PandarGT (mechanical, 60° HFOV, 150° VFOV
forward-facing). Treat as a partial spinning sensor (column_azimuths_rad
spans the 60° wedge).
top_lidar (key sensor for AV reconstruction): Hesai Pandar64,
spinning_direction="cw", 64 beams with non-uniform elevations
(Pandar64 datasheet table — copy the 64 angles, sort descending),
row_azimuth_offsets_rad = zeros(64), 1800 columns.
Data layout per sequence (extract):
<seq_id>/
├── meta/
│ ├── intrinsics/<camera_id>.json # focal, principal point, distortion
│ ├── timestamps.json # per-camera-frame µs
│ └── poses.json # per-frame ego pose (UTM)
├── camera/<camera_id>/<frame>.jpg
├── camera/<camera_id>/poses.json # per-frame camera pose in world
├── lidar/<frame>.pkl.gz # XYZ + intensity + timestamp + ring
└── cuboids/<frame>.pkl.gz # bottom-center xyz + dim + yaw
Conversion checklist:
Pose trajectory: union of per-camera per-frame poses (6 × ~80 = ~480
waypoints) and per-LiDAR-frame poses, deduped + sorted, re-referenced to
the first ego pose.
LiDAR points are world-frame XYZ already ego-compensated → run
MotionCompensator.motion_decompensate_points to recover sensor-frame
per-ray XYZ, then normalise to direction. Per-ray µs from the timestamp
column.
Map raw Pandar64 ring → NCore model_element[:, 0] via a
ring_id → row_index permutation that sorts elevations descending (raw
ring IDs are firing order, not beam index).
Cameras: global shutter (ShutterType.GLOBAL). frame_timestamps_us = [t, t].
NuScenes
No upstream converter — author with Path B. NuScenes ships nested JSON
tables (sample, sample_data, ego_pose, calibrated_sensor, sensor,
sample_annotation, instance).
Sensor inventory:
6 cameras (CAM_FRONT, CAM_FRONT_LEFT, CAM_FRONT_RIGHT, CAM_BACK,
CAM_BACK_LEFT, CAM_BACK_RIGHT) — pinhole. Rolling shutter; consult the
device datasheet for shutter direction (rename to lowercase NCore IDs).
1 LiDAR (LIDAR_TOP): Velodyne HDL-32E, spinning_direction="cw",
32 beams, 1800 columns at 0.2°. Use VLP/HDL-32 datasheet elevations
(descending). row_azimuth_offsets_rad = zeros(32).
A NuScenes "scene" → one V4 sequence. Iterate samples in the scene to
enumerate sample_data per sensor.
Timestamps in sample_data.timestamp are µs already.
ego_pose is rig→world (translation + quaternion). Build the dense
trajectory from the union of ego_pose entries across all sample_data
(cameras at 12 Hz, LiDAR at 20 Hz, radars at 13 Hz → ~50 ms spacing).
calibrated_sensor.translation + .rotation is T_sensor_rig (named
T_calib in their docs — verify direction by transforming a sensor-frame
test point and checking it lands in the expected rig position).
LiDAR .pcd.bin files are already-ego-compensated sensor-frame XYZ + ring
index + intensity. Per-ray timestamps are not stored — synthesise from
column_index (azimuth bin) and the sweep duration (50 ms at 20 Hz):
t_ray = sweep_start + (azim_bin / 1800) * sweep_duration.
sample_annotation: bottom-of-box origin → add size[2]/2 to z.
rotation quaternion → XYZ-Euler radians. instance_token → track_id,
category_name → class_id. LabelSource.EXTERNAL.
Ego masks: NuScenes does not ship them. Generate via SAM2 / off-the-shelf
ego segmentation per camera — strongly recommended for NuRec quality.
Format recipes (non-AV / sensor-only)
These do not have a vehicle rig; pick a body-fixed origin and apply the same
rig conventions (+X forward, +Y left, +Z up).
Mono camera (no depth, no LiDAR) → COLMAP track
You only have RGB images. Run COLMAP first to produce poses + sparse points,
then feed COLMAP into the upstream converter:
COLMAP timestamps are synthetic (1 FPS by default; tune with
--start-time-sec and the FPS embedded in your image filenames).
The COLMAP camera frame already matches NCore (+Z optical) — no rotation
required.
SfM points become a PointCloudsComponent named sfm_points. Use this when
no LiDAR is available so NuRec has a sparse geometric prior.
Ego masks (<image_basename>_mask.png next to images, or --masks-dir).
Stereo cameras
Two synchronised cameras at known baseline. No LiDAR.
Rig origin: midpoint between the two camera optical centres (or the left
camera — pick one and stay consistent).
Static extrinsics: T_left_rig, T_right_rig from your stereo calibration
(OpenCV stereoCalibrate outputs R, T from right-to-left → invert/compose
to get rig-relative).
Trajectory: stereo-VIO (ORB-SLAM3, OpenVSLAM) or COLMAP run on left
images → propagate to rig with T_left_rig.
No LiDAR component. Two options:
Skip LiDAR entirely (set lidar_ids = []). NuRec falls back to
image-only reconstruction (lower quality, more views needed).
Compute disparity per stereo pair → 3-D point cloud per frame in the
left-camera frame → write as a PointCloudsComponent per frame
(analogous to COLMAP sfm_points but dense). This gives NuRec a
geometric prior without faking a spinning LiDAR.
Ego masks: render or hand-paint a static mask of the rig body if visible in
the FOV.
Multi-stereo rig (surround stereo)
Multiple synchronised stereo pairs on one rig (e.g. NVIDIA Hyperion 8.1
surround stereo, AV1, custom inspection robots). Each pair feeds Foundation
Stereo independently to produce dense depth around the platform.
Encode each camera as its ownCameraSensorComponent with a standard
T_camera_rig extrinsic — do not pre-rectify or fuse a pair into a
single virtual sensor. NCore does not have a "stereo pair" component
type; pairing is metadata, not structure.
Declare the pairings on the sequence-levelgeneric_meta_data so
downstream tools (Foundation Stereo, NuRec aux-data) can discover them:
Pose trajectory must include every (camera × frame timestamp) sample —
surround stereo at 8 cameras × 100 frames yields 800 trajectory waypoints,
more than dense enough for per-ray motion compensation. Do not subsample.
Calibration: stereo intrinsics + extrinsics from cv2.stereoCalibrate give
you R, T from right-to-left. Compose with your chosen rig origin to get
T_left_rig and T_right_rig separately; do not store only the
baseline.
Scale is metric by construction (calibrated baseline). Skip scale refinement
(or run it as a sanity check only).
Mono + depth (RGB-D / learned depth)
Single RGB camera + per-frame depth (sensor: RealSense, Kinect, ZED depth, or
learned mono-depth like Marigold / DepthAnythingV2 / MoGe-2).
RGB-D specifics:
RealSense D4xx / L515: active IR stereo (D4xx) or LiDAR-class TOF (L515).
Depth and RGB are co-triggered but not pixel-aligned out of the box —
use the rs2_align filter (or pre-aligned topics) before treating depth
as RGB-frame metric. Intrinsics: read the colour stream's intrinsics for
the RGB component; ignore the depth-stream intrinsics (depth is aligned
into the colour frame).
Microsoft Kinect Azure / Kinect v2: TOF depth with non-trivial
invalidation near object edges. Mask invalidated pixels (depth == 0) before
encoding as a point cloud.
Stereolabs ZED 2 / X: stereo with a built-in disparity engine. Either
store both raw left/right images and treat as a stereo rig (preferred —
Foundation Stereo can re-derive depth at higher quality), or store the
ZED-native depth as a per-frame PointCloudsComponent.
Learned mono-depth (Marigold, DepthAnythingV2, MoGe-2) is scale
ambiguous. Either anchor with one absolute reference (a known object
size, ground-plane height, IMU + visual-inertial scale) before storing,
or accept that scale refinement (r2s module 6) will run downstream.
Rig origin: camera optical centre (or device body if you have a static
IMU offset).
Trajectory: ARKit/ARCore pose stream, IMU+camera VIO, or depth-aided
RGB-D SLAM (Open3D, Spectacular AI).
No LiDAR — depth is not a LiDAR. Two valid encodings:
Per-frame PointCloudsComponent (preferred for learned/stereo-quality
depth, where reliability is uneven). Convert depth + intrinsics →
camera-frame XYZ, transform to world via T_camera_world(t), store as
a point cloud per frame. Carry the dense depth into generic_data if
downstream consumers want it.
Synthetic spinning LiDAR (only if your depth is dense and reliable).
Sample a fixed grid of azimuths/elevations, ray-cast against the depth
map at each frame, and write a LidarSensorComponent. This is more
work and less honest than option 1 — prefer point clouds unless NuRec
specifically needs a LiDAR component.
Camera intrinsics: pinhole or fisheye depending on the lens. Depth-camera
manufacturers ship calibration JSON — copy fx, fy, cx, cy and distortion
coefficients verbatim.
Frame timestamps: depth and RGB are usually co-triggered. Use the RGB
exposure timestamp; depth has no separate component.
Mono + LiDAR (handheld / robot)
Single camera + spinning or solid-state LiDAR, e.g. handheld scanner, ground
robot, drone.
Rig origin: choice driven by mechanical mounting. If the LiDAR is the
reference for ego-motion (LiDAR-inertial SLAM), set rig = LiDAR (so
T_lidar_rig = I). Otherwise pick the IMU body frame or camera centre.
Trajectory: LIO-SAM, FAST-LIO, or any LiDAR-inertial pipeline.
Re-reference to the first frame; cast last (float64 → float32).
Static extrinsics: T_camera_rig from camera-LiDAR calibration
(kalibr, lidar_align). Apply the NCore camera-frame rotation if your
calibration target uses a different convention.
LiDAR:
Spinning (Velodyne / Ouster / Hesai / Robosense / Livox Mid-360 in
repetitive mode): use RowOffsetStructuredSpinningLidarModelParameters
with the sensor's real elevations (datasheet) and "cw". For Ouster
populate row_azimuth_offsets_rad from beam_azimuth_angles.
Solid-state non-repetitive (Livox Avia, Mid-40, Mid-70 in
non-repetitive mode): the spinning model does not fit. Either replay
each scan as a fake "spinning" sweep (stash directions in
column_azimuths_rad per-scan — fragile) or, preferred, write the
points as a PointCloudsComponent per frame in the sensor frame and
skip LidarSensorComponent. NuRec can consume point clouds.
Cuboids: usually unavailable for non-AV — leave the component empty or
unregistered.
Ego masks: render the rig body if it intrudes on the FOV (drone arm,
robot chassis); empty {} if not.
Solid-state / non-repetitive LiDAR (Livox)
Livox Avia / Mid-40 / Mid-70 — and Mid-360 in non-repetitive mode — produce
a point cloud per scan that does not lay out on a row-major spinning
grid. The RowOffsetStructuredSpinningLidarModel does not fit; forcing it
(synthetic columns, fake row bins) breaks NCore validation and
motion-compensation alignment.
Encoding rules:
Preferred — write each scan as a per-frame PointCloudsComponent
instance in the sensor frame, with per-point µs timestamps. Skip
LidarSensorComponent entirely. NuRec consumes point clouds and r2s depth
refinement (module 7) treats them as it would LiDAR sweeps.
Fallback for repetitive Mid-360 — the Mid-360 in repetitive mode does
produce a structured grid; treat it as a spinning LiDAR with the
datasheet's beam table and spinning_direction="cw". This is the only
Livox variant the spinning model fits.
IMU is not stored as its own NCore component — it densifies the pose
trajectory (and, optionally, anchors metric scale on monocular setups). Two
paths:
VIO trajectory (preferred): run a visual-inertial pipeline (cuVSLAM
stereo-inertial, ORB-SLAM3, OpenVSLAM, OpenVINS, Spectacular AI) →
IMU-rate (100–200 Hz) T_world_rig poses → store as the dynamic pose.
The trajectory is already dense enough that per-ray motion compensation
works without further densification.
IMU integration only (bootstrap / fallback): pre-integrate IMU
(linear accel + angular vel) over short windows, anchor each window with
the next available camera- or LiDAR-rate pose. Useful for filling gaps or
extrapolating to per-LiDAR sweep timestamps when the SLAM stack only
emits poses at frame rate.
Either way, IMU sample timestamps go into the pose trajectory, not into
a separate component. If a downstream consumer wants raw IMU, stash the
samples in the sequence-level generic_meta_data["imu_samples"] (compact)
or in a sidecar file referenced from there.
Calibration: IMU-to-camera and IMU-to-LiDAR extrinsics live in the static
pose graph as T_imu_rig = I if you take the IMU body frame as the rig
(common for legged robots and drones), with T_camera_rig /
T_lidar_rig from kalibr / lidar_align outputs. Pick rig = IMU when
the IMU is the trajectory reference; otherwise pick the mechanical body
frame and store T_imu_rig for downstream tools that want IMU-frame data.
ROS2 bag (MCAP / SQLite3)
Most robotics datasets ship as ROS2 bags. The standard path is the
rosbags Python library — no rclpy and no native ROS install required:
pip install rosbags pyav # pyav decodes H.264 video chunks; rosbags handles .mcap and .db3
Convert in two passes: first enumerate sensors and collect calibration /
the static TF tree, then stream frames into the V4 writer. Common topic →
component mapping:
ROS2 message type
NCore mapping
sensor_msgs/Image (raw)
CameraSensorComponent.store_frame — re-encode to JPEG with PIL before storing (NCore stores bytes verbatim; raw bitmaps balloon the store)
sensor_msgs/CompressedImage
CameraSensorComponent.store_frame — pass data directly with image_format="jpeg" or "png"
foxglove_msgs/CompressedVideo (H.264 chunks)
Decode with PyAV (av.open(BytesIO(...))) → re-encode each frame to JPEG → store
sensor_msgs/CameraInfo
Source for OpenCVPinholeCameraModelParameters (or fisheye) — K, D, width/height
tf2_msgs/TFMessage
Read once, build the static TF tree (rosbags' built-in TF helper), derive T_sensor_rig per camera/lidar
Trajectory densifier only — integrate or feed into VIO; never stored as its own NCore component
sensor_msgs/PointCloud2
LiDAR sweep — per-point fields (x, y, z, intensity, ring, t) map to direction = xyz / norm, intensity, model_element[:, 0] = ring. If t is absent, synthesise from sweep duration and azimuth bin (see Mono + LiDAR notes).
livox_ros_driver2/CustomMsg
Livox custom format — same as PointCloud2 plus per-point offset_time (ns from sweep start). Solid-state non-repetitive scans go into PointCloudsComponent, notLidarSensorComponent (see solid-state recipe).
Notes:
Rolling-shutter ROS2 cameras: Image.header.stamp is the frame trigger.
Compute [exposure_start, exposure_end] from CameraInfo exposure metadata
if present, otherwise read the device datasheet. Setting
frame_timestamps_us = [trigger, trigger] is acceptable for
well-synchronised global-shutter rigs, wrong for rolling-shutter
unless the readout time is small enough to ignore.
TF tree → rig frame: pick base_link (or whichever frame is configured
as the robot body) as rig. ROS REP 105 (x forward, y left,
z up) matches NCore's rig convention exactly — no rotation needed.
The rosbags API opens both MCAP and SQLite3 with the same code path;
only the file extension differs.
For multi-bag datasets (one bag per take), one bag = one V4 sequence.
Keep the bag's recording timestamps (not wall-clock playback) — bag
timestamps are µs-quantised already, perfect for NCore.
Aerial / drone
Drones add three failure modes on top of the standard mono+lidar / stereo
recipes:
Fast rotation: pose trajectory must densify enough to keep angular
drift per waypoint below ~0.5°. At 100 °/s yaw rate, that means
waypoints every 5 ms — much tighter than a typical 10 Hz LiDAR. Use IMU
samples (200 Hz+) as the trajectory backbone; do not rely on per-LiDAR
poses alone.
Rolling-shutter cameras are common on consumer drones. Set
ShutterType.ROLLING_TOP_TO_BOTTOM, supply real [exposure_start, exposure_end] per frame, and carry the per-row shutter delay into the
intrinsics if your model supports it (shutter_delay_us on
OpenCVPinholeCameraModelParameters for FTheta-like models).
Wide altitude / range: a 5+ km loop in raw UTM at the end of the
flight loses the same precision that the AV first-pose re-referencing
fixes. For continuous takes under ~2 km, re-reference once to the
takeoff pose; for longer flights, segment the bag and emit one V4
sequence per segment.
Rig origin on a drone: IMU body frame is the canonical choice. All
extrinsics are then T_sensor_imu. Rotor masks are usually unnecessary —
rotors blur out of the FOV at flight RPM — but include a static mask of any
fixed gimbal arm visible in the FOV.
Robotics pipeline shards (r2s)
The r2s ("robotics-to-sim") pipeline chains NCore through pose, depth, mask,
and refinement steps before NuRec. Each step writes its own NCore shard
so that any module can be swapped, re-run, or skipped without rebuilding the
preceding stages. If you're authoring a converter that feeds r2s — or a
downstream module that reads/writes intermediate shards — follow this
naming + content contract.
per-frame PointClouds named depth_<camera_id> (one entry per keyframe)
Until a first-class DepthComponent lands in V4, encode dense depth as a per-frame point cloud (camera-frame XYZ from depth + intrinsics). Stash uint16 mm depth in generic_data["depth_mm"] for tools that want pixel-aligned access.
{name}.masks.zarr.itar
Semantic Mask Generation (SAM2 / Grounded-SAM)
Masks (per-camera, per-keyframe)
Masks here are semantic (sky, ground, dynamic-object), not just ego-vehicle. Ego masks may live alongside in the same component instance.
{name}.poses.scaled.zarr.itar
Scale Refinement
Poses with generic_meta_data.scale_factor and per-frame bias
Same trajectory schema as {name}.poses.zarr.itar; recovered scale + per-frame bias recorded in metadata.
{name}.depth.refined.zarr.itar
Depth Refinement
per-frame PointClouds (refined)
Same component layout as {name}.depth.zarr.itar, with cross-frame scale/bias and occlusion removal applied.
{name}.sim.zarr.itar
Sensor-Data Simulation (NuRec renderer)
CameraSensor, Poses, Intrinsics matching the target trajectory
Same schema as a real base shard — directly consumable by any module. Always tag generic_meta_data.source = "simulation".
Component encoding until V4 ships first-class depth / mappoints
The r2s spec references two components that are not yet in upstream V4:
DepthComponent (per-pixel uint16 depth, mm, per camera per keyframe).
Dense depth → per-frame PointCloudsComponent, instance name
depth_<camera_id>, points in the camera frame at the keyframe
timestamp. Carry the raw uint16 depth array in
generic_data["depth_mm"] if downstream tools need pixel-aligned access.
SfM map → a single PointCloudsComponent instance named
sfm_points (already produced by the upstream COLMAP converter).
Per-frame observation tracks, when needed, go in
generic_meta_data["track_observations"].
Treat these as forward-compatible encodings: when V4 adds the first-class
components, the migration path is mechanical (copy the same arrays into
the new writer) and the data shape is already correct.
Validator hooks
Each module's validator runs after its shard is written. The spec
assertions that map onto NCore writer-time checks are already enforced
(timestamp ordering, valid intrinsics, pose-trajectory completeness,
strict-increasing LiDAR azimuths). The remaining checks (depth value range,
mask temporal consistency, scale factor bounds, etc.) are the module's
responsibility — see the r2s modules.md for the canonical list of per-step
validations.
Validation & end-to-end NuRec
After every conversion, before assuming success:
ncore_vis — visualise the store. Wrong sensor extrinsics, mirrored
LiDAR (spinning_direction flip), or rotated cameras are obvious here.
ncore_project_pc_to_img — projects LiDAR onto camera frames. Crisp
alignment confirms T_lidar_rig, T_camera_rig, intrinsics, per-ray
timestamps, and pose-trajectory density are all correct simultaneously.
Smearing or doubling = motion-comp error (per-ray timestamps wrong, or
pose trajectory too sparse).
NuRec end-to-end. Hand the converted store to the
nre sibling skill — Workflow A wires together
aux-data generation (via nre-tools), 3DGUT training, USDZ export,
and novel-view rendering, and references/configuration.md documents
how to override dataset.camera_ids / dataset.lidar_ids so the
training Hydra recipe matches your sensor IDs. For repeatable cluster
runs, wrap the convert + train + export sequence in an OSMO / Slurm /
Kubernetes pipeline that pins both the
NVIDIA/ncore and NRE container
versions.
NuRec's "Ensure Data Quality" doc (in the NuRec image) also lists
check_lidar_camera_sweep_alignment and other validators you can run
post-conversion.
Troubleshooting (common failure modes and the fix file)
The canonical fixes live in code (example_converter.py inline comments) and
in the spec; most "NuRec produced garbage" complaints reduce to one of:
Symptom (NuRec / ncore_vis)
Almost-always cause
Fix
Z-flipped surfaces
spinning_direction wrong
Set "cw" for all common automotive spinning LiDARs
Whole point cloud rotated horizontally
column_azimuths_rad starting at 0 instead of real heading
Derive azimuths from per-column pose data, or rotate T_lidar_rig to compensate (consistently)
Strict-increasing assert in NCore writer
LiDAR elevations ascending or contain duplicates
Sort descending, nudge duplicates by 1e-6 rad
"Dynamic poses must cover the full sequence time range"
Sequence interval built with from_start_end(start, end + 1)
Pass real inclusive end; the helper internally adds 1
RuntimeError: double != float at "Get Lidar Point Clouds"
T_camera_rig / T_lidar_rig written as float64
Cast extrinsics to float32 (only world_world_global stays float64)
Reconstruction loses sub-cm detail at scene scale
Poses not re-referenced; raw UTM/ECEF cast to float32
poses = inv(poses[0]) @ poses in float64, then cast
Motion-comp blur / rowing artefacts
Pose trajectory too sparse
Combine all available pose sources (every camera × every frame, plus IMU/GPS), unique + sort
Ghosting / motion blur on rolling-shutter cameras
Single global timestamp used for all cameras, or ShutterType.GLOBAL set on rolling sensor
Per-camera per-frame [exposure_start, exposure_end]; map shutter direction by enum name
Generate per-camera binary ego mask; pass via MasksComponent.store_camera_masks
LiDAR projects 50 ms ahead of camera
Frame-start used as sweep midpoint (or vice versa)
frame_timestamps_us[0] = real sweep start; per-ray timestamp_us linear in column
Foundation Stereo (or aux-data) cannot find its pair
Missing stereo_pairs on sequence generic_meta_data
Set generic_meta_data={"stereo_pairs": [{"left": ..., "right": ...}]} on SequenceComponentGroupsWriter
Livox scan stored as a LidarSensorComponent but most rays read range 0
Solid-state non-repetitive doesn't have a column grid
Use per-frame PointCloudsComponent (sensor-frame XYZ + per-point µs); skip LidarSensorComponent
Drone reconstruction shows streaks / motion smear
Trajectory densified at LiDAR rate (10 Hz) on a 200 °/s yaw motion
Use IMU samples (200 Hz+) as trajectory backbone; merge per-frame poses on top
ROS2 raw-Image topic blows up store size 30×
Stored bitmap bytes verbatim instead of re-encoding to JPEG
PIL-encode each sensor_msgs/Image to JPEG before store_frame; use image_format="jpeg"
Pipeline downstream module sees real data instead of sim
Renderer-output shard missing source tag
Set generic_meta_data["source"] = "simulation" (and "model_checkpoint") on the simulated sequence shard
IMU samples written into a "sensor" component and rejected by NuRec
IMU is not a first-class V4 component
Drop IMU samples into the pose trajectory (or generic_meta_data["imu_samples"]); never register an IMU writer
Limitations
No first-class IMU component. V4 has no IMU sensor type — IMU
samples must ride in the pose trajectory or in generic_meta_data
(never as a sensor writer).
Per-ray LiDAR is the only motion-comp-safe option for spinning
LiDARs. If the dataset only gives frame-level timestamps, expect
motion-blur smearing in NuRec; reconstruct per-ray timestamps from
azimuth or accept the artefact.
Sub-cm scene detail at world scale requires float64 pose math
followed by re-referencing (poses = inv(poses[0]) @ poses)
before writing as float32. Raw UTM/ECEF casts to float32 will
silently lose centimetre-scale geometry.
Rolling-shutter cameras need per-camera per-frame
[exposure_start, exposure_end]and the correct ShutterType
by enum name — a single global timestamp will produce ghosting.
Solid-state non-repetitive LiDAR (Livox-style) must use
PointCloudsComponent, not LidarSensorComponent (the latter
assumes a column grid).
The converter is one-way. There is no v4 → original tool;
always keep the source dataset alongside.
This skill is convert + validate only. Training, rendering, or
USDZ packaging is the nre skill's job.
