Reading Pointcloud from .pcd to ROS PointCloud2

Question

I want to create a simple python script to read some.pcd files and create a sensor_msgs::PointCloud2 for each in a rosbag.

I tried using the python-pcl library, but I'm probably doing something wrong when adding the points to the data field, because when playing the rosbag and checking with RViz and echoing the topic I get no points.

This is the part where I set the PointCloud2 msg.

pcl_data = pcl.load(metadata_dir + "/" + pcd_path)

# get data
pcl_msg = sensor_msgs.msg.PointCloud2()
pcl_msg.data = np.ndarray.tobytes(pcl_data.to_array())
pcl_msg.header.stamp = rospy.Time(t_us/10000000.0)
pcl_msg.header.frame_id = "robot_1/navcam_sensor"

# Pusblish Pointcloud2 msg
outbag.write("/robot_1/pcl_navcam", pcl_msg, rospy.Time(t_us/10000000.0))

I also tried pypc without any luck as well.

How would you do it? Maybe there is a ToROSMsg method somewhere like in the cpp version of pcl?

Is there a python equivalent for what is very easily available in cpp: pcl::toROSMsg?

Thank you

Here is the full code of the python script:

#! /usr/bin/env python3

import rospy
import rosbag
import tf2_msgs.msg
import geometry_msgs.msg
import sensor_msgs.msg
import sys
import os
import json
import numpy as np
import tf.transformations as tf_transformations
import pcl
import json
import math
import pypcd
import sensor_msgs.point_cloud2 as pc2
import tf2_msgs.msg._TFMessage


def main():
    output_bag_path = dataset_path + "rosbag.bag"
    with rosbag.Bag(output_bag_path, 'w') as outbag:
        
        # iterate metadata files with tfs
        metadata_dir = dataset_path + "Pointcloud/metadata"
        t_first_flag = False

        # for filename in os.listdir(metadata_dir):
        list_of_files = sorted( filter( lambda x: os.path.isfile(os.path.join(metadata_dir, x)),
                        os.listdir(metadata_dir) ) )
        for filename in list_of_files:

            # open json file
            json_path = os.path.join(metadata_dir, filename)
            json_file = open(json_path)
            json_data = json.load(json_file)

            # get timestamp 
            t_us = json_data \
                ["metadata"] \
                ["Timestamps"] \
                ["microsec"]
            t_ns, t_s = math.modf(t_us/1000000)

            # get camera tf
            pos = geometry_msgs.msg.Vector3( \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["translation"][0], \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["translation"][1], \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["translation"][2])
            quat = geometry_msgs.msg.Quaternion( \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["orientation"] \
                ["x"], \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["orientation"] \
                ["y"], \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["orientation"] \
                ["z"], \
                json_data["metadata"] \
                ["pose_robotFrame_sensorFrame"] \
                ["data"] \
                ["orientation"] \
                ["w"], )
            navcam_sensor_tf = geometry_msgs.msg.TransformStamped()
            navcam_sensor_tf.header.frame_id = "reu_1/base_link"
            navcam_sensor_tf.child_frame_id = "reu_1/navcam_sensor"
            navcam_sensor_tf.header.stamp = rospy.Time(t_us/1000000.0)
            navcam_sensor_tf.transform.translation = pos
            navcam_sensor_tf.transform.rotation = quat

            # get base_link tf
            pos = geometry_msgs.msg.Vector3( \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["translation"][0], \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["translation"][1], \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["translation"][2])
            quat = geometry_msgs.msg.Quaternion( \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["orientation"] \
                ["x"], \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["orientation"] \
                ["y"], \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["orientation"] \
                ["z"], \
                json_data["metadata"] \
                ["pose_fixedFrame_robotFrame"] \
                ["data"] \
                ["orientation"] \
                ["w"], )
            base_link_tf = geometry_msgs.msg.TransformStamped()
            base_link_tf.header.frame_id = "map"
            base_link_tf.child_frame_id = "reu_1/base_link"
            base_link_tf.header.stamp = rospy.Time(t_us/1000000.0)
            base_link_tf.transform.translation = pos
            base_link_tf.transform.rotation = quat

            # publish TFs
            tf_msg = tf2_msgs.msg.TFMessage()
            tf_msg.transforms = []
            tf_msg.transforms.append(base_link_tf)
            outbag.write("/tf", tf_msg, rospy.Time(t_us/1000000.0)) 
            tf_msg = tf2_msgs.msg.TFMessage()
            tf_msg.transforms = []
            tf_msg.transforms.append(navcam_sensor_tf)
            outbag.write("/tf", tf_msg, rospy.Time(t_us/1000000.0))

            # open corresponding .pcd file
            pcd_path = json_data["data"]["path"]
            pcl_data = pcl.load(metadata_dir + "/" + pcd_path)
            # pcl_data = pypcd.(metadata_dir + "/" + pcd_path)

            # get data
            pcl_msg = sensor_msgs.msg.PointCloud2()
            pcl_msg.data = np.ndarray.tobytes(pcl_data.to_array())
            pcl_msg.header.stamp = rospy.Time(t_us/1000000.0)# t_s, t_ns)
            pcl_msg.header.frame_id = "reu_1/navcam_sensor"
         
            # Pusblish Pointcloud2 msg
            outbag.write("/reu_1/pcl_navcam", pcl_msg, rospy.Time(t_us/1000000.0))

        pass



if __name__ == "__main__":

    dataset_path = "/home/---/Documents/datasets/---/" 

    main()

The base_link and camera tfs come from a json file that also stores a string to associate the.pcd file.

Answer 1

One issue with the code you posted is that it only creates one PointCloud2 message per file . That being said, there is already a package to do what you're hoping, check out this pcl_ros module . You can create a PointCloud2 message and publish it with rosrun pcl_ros pcd_to_pointcloud <file.pcd> [ <interval> ] .

Also as of note: if you're running a full ROS desktop install you don't actually need to install pcl libraries individually; they're baked into the default ROS install.