False semantic data for lidar range sensor

Dear NVIDIA team,
I’m working on generating a custom dataset with labeled pointclouds. As stated in the Range-Sensor API, the get_semantic_data function returns the semantic id of the hit for each beam in uint16.
To test that I build a very easy scene with a LiDAR and a camera inside the warehouse sample environment. The only semantic class is given to a cube. Here is a picture of the scene:

The camera view is as follow, on the right the lidar parameters are visible:

I added a transform component to the cube that changes the x,y and z coordinate. Not the rotation tho. To extract the Information I need I utilize the Python API. I randomize the scene in total 10 times and after each iteration I wait 5 seconds for the scene to fully load. This was stated to might be a problem here. Furthermore I included a time.sleep() as proposed in this forum entry.
The problem I am facing is that the semantic data that is returned does not entirely match the cube! To show what I mean I plotted the pointcloud, (which looks very promising) and emphasized the specific points that are labeled to be “on the cube” in color yellow.
First of all the bbox2D & semantic groundtruth for scene 1 and 9

Semantic-Scene 1

BBox-Scene 9

Semantic-Scene 9

Everything looks very nice. Now the plotted Pointcloud with emphasized labels in yellow for both scenes:
Pointcloud + labels for class cube in yellow - Scene 1:

Pointcloud + labels for class cube in yellow - Scene 2:

Finally the code that I am using to generate the data:

# Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.
# NVIDIA CORPORATION and its licensors retain all intellectual property
# and proprietary rights in and to this software, related documentation
# and any modifications thereto.  Any use, reproduction, disclosure or
# distribution of this software and related documentation without an express
# license agreement from NVIDIA CORPORATION is strictly prohibited.

"""Generate offline synthetic dataset

import asyncio
import copy
import os
import torch
import signal
import numpy as np
import carb
import omni
import time
from omni.isaac.python_app import OmniKitHelper
import random
import math

# Default rendering parameters
    "renderer": "RayTracedLighting",
    "samples_per_pixel_per_frame": 12,
    "headless": False,
    "experience": f'{os.environ["EXP_PATH"]}/omni.isaac.sim.python.kit',
    "width": 1280,
    "height": 720,

class RandomScenario(torch.utils.data.IterableDataset):
    def __init__(self, scenario_path, writer_mode, data_dir, max_queue_size, train_size, classes):

        self.kit = OmniKitHelper(config=RENDER_CONFIG)
        #Imports AFTER OmniKitHelper is initialized! -> https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/python_environment.html#omnikithelper
        from omni.isaac.synthetic_utils import SyntheticDataHelper, DataWriter, KittiWriter, DomainRandomization
        # import the python bindings to interact with lidar sensor
        from omni.isaac.range_sensor import _range_sensor
        self.sd_helper = SyntheticDataHelper()
        self.dr_helper = DomainRandomization()

        self.writer_mode = writer_mode
        self.writer_helper = KittiWriter if writer_mode == "kitti" else DataWriter
        self.result = True

        self.scenario_path = "/home/jan-oliver/Documents/Bachelor_Thesis/IsaacSim/ARIBIC_scene/sensorrack_test_labels.usd"
        scenario_path = self.scenario_path

        self.max_queue_size = max_queue_size
        self.data_writer = None
        self.data_dir = data_dir
        self.train_size = train_size
        self.classes = classes

        self.cur_idx = 0
        self.exiting = False
        self._sensor_settings = {}

        #Interface to communicate with the lidar
        self.lidarInterface = _range_sensor.acquire_lidar_sensor_interface()
        self.timeline = omni.timeline.get_timeline_interface()
        self.stage = self.kit.get_stage()
        signal.signal(signal.SIGINT, self._handle_exit)

    def _handle_exit(self, *args, **kwargs):
        print("exiting dataset generation...")
        self.exiting = True

    async def load_stage(self, path):
        await omni.usd.get_context().open_stage_async(path)

    def _setup_world(self, scenario_path):
        # Load scenario and start playing
        print("Loading scene from: ", scenario_path)
        setup_task = asyncio.ensure_future(self.load_stage(scenario_path))
        while not setup_task.done():

    def __iter__(self):
        return self
    def __next__(self):
        ''' Randomize the scene once '''
        # step once and then wait for materials to load
        while self.kit.is_loading():

        #Keep waiting for a couple more seconds.
        update_task = asyncio.ensure_future(self.async_sleep(5))
        print("Waiting for scene to fully load!")
        while not update_task.done():
        print("Finished waiting")

              Default implementation to obtain other sensor data using gt = self.sd_helper.get_groundtruth(gt_list, viewport)

        viewport_iface = omni.kit.viewport.get_viewport_interface()
        viewport_name = "Viewport"
        viewport = viewport_iface.get_viewport_window(viewport_iface.get_instance(viewport_name))

        ''' Get the Lidar data and combine it in one array. '''
        #LiDAR setup for interaction
        self.lidar_path = "/Root/ARIBIC/velodyne_puck"
        if not self.lidarInterface.is_lidar_sensor(self.lidar_path):
            print("ERROR: Lidar sensor is not valid!")
        # Note:
        # get_intensity_data() -> Only returns a value of 255, if it was a hit or 0 if it was no hit. It is mostly a hit because the range is at 100 meters.
        # Therefore this information is not very useful to us.
        # get_depth_data -> The distance from the sensor to the hit for each beam in uint16 and scaled by min and max distance
        # Dividing by 65535 and multiplying by 255 returns the intensitiy for a visualization in an image
        #Sleep to copy gpu buffers? -> https://forums.developer.nvidia.com/t/get-sensor-data-from-isaac-sim/165169/2
        #Keep waiting for a couple more seconds.
        pointcloud = self.lidarInterface.get_point_cloud_data(self.lidar_path)  #In cm = Unit that is used in Isaac
        pointcloud = self.get_meters_per_unit() * pointcloud
        labels = self.lidarInterface.get_semantic_data(self.lidar_path)
        intensities = self.lidarInterface.get_depth_data(self.lidar_path)
        lidar_data = self.reshapeAndCombineLidarData(pointcloud,labels,intensities)
        print("Point Cloud dimensions:", pointcloud.shape)
        print("Labels array dimensions: ", labels.shape)
        print("Intensities array dimensions: ", intensities.shape)
        print("Combined array dimensions: ", lidar_data.shape)
        #Store the Lidar data
        lidar_data_storage_folder = self._output_folder + "/" + viewport_name +"/lidar"
        self.storeLidarData(lidar_data, lidar_data_storage_folder)

        Calculate and store the camera extrinsic and intrinsic matrices

        self.cur_idx += 1
        return image

    async def async_sleep(self, duration):
        await asyncio.sleep(duration)
    def get_meters_per_unit(self):
        from pxr import UsdGeom
        stage = omni.usd.get_context().get_stage()
        return UsdGeom.GetStageMetersPerUnit(stage)

        Stores the lidar data as .npy file in the specified folder
            path        -> Path to the !Folder! where the files are stored in. Do not specify the name for the file!
            lidar_data  -> Array containing the lidar data
            None        -> Just stores the data as path/{curent_iteration_index}.npy 
    def storeLidarData(self, lidar_data, path):
        # Create directory
            print("Directory " , path ,  " created ") 

        except FileExistsError:
            print("Directory to store lidar data - " , path ,  " - already exists")
        #Store the data
        lidar_data_file_name = path + "/" + str(self.cur_idx) + ".npy"
        with open(lidar_data_file_name, 'wb') as f:
            np.save(f, lidar_data)
        print("Saved lidar data successfully as: ", lidar_data_file_name)

        Takes the lidar data and returns a combined 2d array
            pointcloud  [a,b,c] ->  a = amount of horizontal sensor readings, 
                                ->  b = amount of vertical sensor readings,
                                ->  c = amount of dimensions per point - x,y,z
            labels      [a,b]   ->  a = amount of horizontal sensor readings, 
                                ->  b = amount of vertical sensor readings
            intensities [a,b]   ->  a = amount of horizontal sensor readings, 
                                ->  b = amount of vertical sensor readings
        Output: [d,e]           ->  d = a * b , total amount of sensor readings
                                ->  e = c + 1 + 1, namely x,y,z,intensity,label for specific reading
    def reshapeAndCombineLidarData(self, pointcloud, labels, intensities):
        pc_resh = self.reshapePointcloud(pointcloud)
        labl_resh = self.reshapeLabelsAndIntensity(labels)
        int_resh = self.reshapeLabelsAndIntensity(intensities)
        data = np.concatenate((pc_resh,int_resh, labl_resh),axis=1)
        return data
        Takes the lidar pointcloud and returns reshaped array
            pc [a,b,c]  ->  a = amount of horizontal sensor readings, 
                        ->  b = amount of vertical sensor readings,
                        ->  c = amount of dimensions per point - x,y,z
        Output: [d,e]   ->  d = a * b, amount of total sensor readings
                        ->  e = c, amount of dimensions per point - x,y,z
    def reshapePointcloud(self, pc):
        total_points = pc.shape[0] * pc.shape[1]
        points_dimension = pc.shape[2]
        pc_2d = np.reshape(pc, (total_points,points_dimension))
        return pc_2d

        Takes the lidar labels or intensities and returns reshaped array
        Input: [a,b]    ->  a = amount of horizontal sensor readings, 
                        ->  b = amount of vertical sensor readings
        Output: [c,1]   ->  c = a * b, amount of total sensor readings
    def reshapeLabelsAndIntensity(self, array_2d):
        total_points = array_2d.shape[0] * array_2d.shape[1]
        pc_2d = np.reshape(array_2d, (total_points,1))
        return pc_2d

if __name__ == "__main__":
    "Typical usage"
    import argparse

    parser = argparse.ArgumentParser("Dataset generator")
    parser.add_argument("--scenario", type=str, help="Scenario to load from omniverse server")
    parser.add_argument("--num_frames", type=int, default=10, help="Number of frames to record")
    parser.add_argument("--writer_mode", type=str, default="npy", help="Specify output format - npy or kitti")
        "--data_dir", type=str, default=os.getcwd() + "/output", help="Location where data will be output"
    parser.add_argument("--max_queue_size", type=int, default=500, help="Max size of queue to store and process data")
        "--train_size", type=int, default=8, help="Number of frames for training set, works when writer_mode is kitti"
        help="Which classes to write labels for, works when writer_mode is kitti.  Defaults to all classes",
    args = parser.parse_args()

    dataset = RandomScenario(
        args.scenario, args.writer_mode, args.data_dir, args.max_queue_size, args.train_size, args.classes

    if dataset.result:
        # Iterate through dataset and visualize the output
        print("Loading materials. Will generate data soon...")
        for image in dataset:
            print("ID: ", dataset.cur_idx)
            if dataset.cur_idx == args.num_frames:
            if dataset.exiting:
        # cleanup

I really hope you can point out to me what I am missing :/. Thank you so much!


Thanks for reporting this issue, I’ve filed a bug for us to take a closer look at it

I think the problem might be that the lidar has horizontal scans, while the pointcloud has a different set of points. Thus, merging them might bring discrepancies. It might be better to merge the depth map with the semantic.

Thank you @Hammad_M !

in 2021.2.0 you can now publish depth point cloud PCL message directly from the Isaac Sim ROS camera publisher, This might make it easier to align the point cloud to the semantic image also published from the ROS camera publisher (similar to what @eliabntt94 suggests)

Hi Hammad.
Just to clarify: I’m not intending to use the LIDAR sensor with ROS in any way. I just want to obtain the LIDAR scans and the matching semantics for each LIDAR-Point.

Using the newest Isaac Sim Version I have two problems:
Error/Bug 1:
Actually this is still the same problem/bug as before.
I was able to adapt the code to work with the updated Isaac Sim Version.
To demonstrate the “bug?” I am using the basic warehouse example provided.
Using this environment, I am both using the synthetic data generator to retrieve things such as 2D bboxes and depth map, and the lidar API to obtain the pointcloud and corresponding semantics.
An example of the semantics I obtain using this approach:

Types & IDs from synthetic data generator:  {('box', 3), ('floor', 10), ('cart', 19), ('wall', 12), ('floor_decal', 5), ('crate', 9), ('lamp', 17), ('fire_extinguisher', 18), ('fuse_box', 15), ('sign', 14), ('pillar', 6), ('wire', 8), ('klt_bin', 1), ('pallet', 4), ('rack', 2), ('barcode', 11), ('bracket', 7)}

Labels contained in lidar semantics:  {0.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 9.0, 12.0, 14.0, 17.0, 18.0, 19.0}

Plotting for example the lidar semantics that correspond to “pillar” I obtain the following:

This looks somewhat correct.
Plotting “pallet” I obtain this:

This doesn’t look correct (f.ex. the dots on the floor are marked as “on pallet”), which leads me to the conclusion that the bug with the lidar labels isn’t fixed in this version.
Error/Bug 2:
With the new version, the LIDAR semantics simply ignore semantics I assigned to objects. The provided environment has every component already labeled. This is recognized by the LIDAR semantics as shown above. Still, if I go ahead and just add a Mesh Cube and assign a custom class label, this is no longer considered in the semantics of the LIDAR. The synthetic data API on the other hand does consider them.
Right here I have highlighted the label given to an element in the scene. Special focus on how the the label is called in the Semantics Schema Editor → Semantics: class pallet

On the other hand, if I define a custom label, the name of the Semantics in the Semantics Schema Editor is something different, namely Semantics_ys5g: class cube

The problem now is, that the second label is no longer considered by the lidar semantics. To show that I again output all the labels that are present in the lidar semantics, as well as returned by the synthetic data API.

Types & IDs from synthetic data generator:  {('rack', 7), ('crate', 10), ('klt_bin', 1), ('sign', 13), ('cart', 19), ('pillar', 5), ('bracket', 6), ('fire_extinguisher', 15), ('pallet', 3), ('wire', 8), ('box', 2), ('floor', 9), ('cube', 20), ('floor_decal', 4), ('barcode', 11), ('wall', 12), ('fuse_box', 17), ('lamp', 18)}

Labels contained in lidar semantics:  {0.0, 2.0, 3.0, 4.0, 5.0, 7.0, 8.0, 10.0, 12.0, 13.0, 15.0, 18.0, 19.0}

As one can see: The 2D BBoxes contain an entry with the id 20 → cube. On the other hand, the lidar data does not!
To prove that the cube is actually “hit” by the lidar beam I projected the lidar pointcloud into the image:

It is obvious that the semantics should contain entries for the label “cube”.

Maybe I am doing something wrong assigning the semantics?. Thank you very much for your help.


@jan-oliver still working on error 1, but for error 2, does this notebook reproduce your usecase?
you can run it via ./jupyter_notebook.sh lidar_semantics.ipynb
(the cells to start SimulationApp and create the environment might take a bit of time to run)

lidar_semantics.ipynb (76.5 KB)

I’m seeing the cube and sphere in both the lidar and camera semantics, but there might be something missing from my test.

Hi @Hammad_M, if I add LiDAR into Jetbot, and add semantics information for objects. When the Jetbot moves, the point moved from the object to the ground will remain its original semantic ID.

Like the image, the ground points should be red rather than blue.
The original code is here, could you help me to check whether it is a bug or anything that I did wrong? And if directly move lidar position, there is no problem like this.
lidar_semantics.py (7.1 KB)