Incorrect events decoding

[andberto]

Hi, I'm trying to decode events from a ROS bag recorded with the sensor Prophesee EVK4 (IMX636) so the event codec should be EVT3.0. Using the example provided I obtain events that are not correct (i.e x > senso_with, y > sensor_height, polarity not in {-1, 1} wrong timestamps).

Here's my code:

import argparse
import glob
import os
from bag_reader_ros2 import BagReader
from event_camera_py import Decoder

def extract_bag(input, output, event_topic):
    bag = BagReader(input, event_topic)
    decoder = Decoder()
    while bag.has_next():
        topic, msg, t_rec = bag.read_next()
        print(topic)
        decoder.decode_bytes(msg.encoding, msg.width, msg.height,
                             msg.time_base, msg.events.tobytes())
        cd_events = decoder.get_cd_events()
        print(cd_events)

def main(args=None):
    parser = argparse.ArgumentParser()
    parser.add_argument("path", help="ROS 2 bag file to extract or directory containing bags")
    parser.add_argument("--output_dir", default="/tmp/extracted_data", help="Folder where to extract the data")
    parser.add_argument("--events_topic", default="/event_camera/events", help="Event camera topic")
    args = parser.parse_args()

    bag_path = ''

    print(f'Data will be extracted in folder: {args.output_dir}')
    if not os.path.exists(args.output_dir):
        os.makedirs(args.output_dir)
    if os.path.isdir(args.path):
        bag_path = sorted(glob.glob(os.path.join(args.path, "*.db3")))[0]
    else:
        bag_path = args.path

    extract_bag(input = bag_path, output = args.output_dir, event_topic = args.events_topic)

if __name__ == '__main__':
    main()

Some events i'm obtaining:

[( 879, 16, 0, 5962275) (59904, 16948, 37, 14287178) (64039, 90, 116, 1110764033) ... (32480, 16922, 100, -1017008928) (24158, 52683, 1, 449) (32480, 16922, 100, -1017008928)]

Thank you in advance for the help.

[berndpfrommer]

Not much to go by from this. The first question to settle: is this a problem with the python decoding, or is the data already bad. To find out, please run an event camera renderer node and display the events when played back from a rosbag. Does the display of events look good? Also, there is the event_ros_tools package that has a tool to dump the decoded data packets. Can you use that to decode? Do those packets also show the problem? I see you are using decode_bytes(). What if you avoided it like this, would that work?

from bag_reader_ros2 import BagReader
from event_camera_py import Decoder

topic = '/event_camera/events'
bag = BagReader('foo', topic)
decoder = Decoder()

while bag.has_next():
    topic, msg, t_rec = bag.read_next()
    decoder.decode(msg)
    cd_events = decoder.get_cd_events()
    print(cd_events)
    trig_events = decoder.get_ext_trig_events()
    print(trig_events)

[andberto]

I've tried with the camera renderer and the events are displayed correctly, also with the dump tool from event_camera_tools the events are correct. I've tried your code snippet but the output is the same as mine. So the problem is with the python decoding i guess.

[berndpfrommer]

Would you mind sending me a ros2 bag that shows the problem? The shorter the better.

[andberto]

bag.zip Here's a shortened version.

[berndpfrommer]

I ran the following code on your bag and it did not raise an exception. Strange. Could be a systems problem.

• what ROS2 version are you running, what OS, what hardware (x86_64 or arm64)?
• did you install the module from the apt repository? I used the latest "master" branch from github source.

from bag_reader_ros2 import BagReader

from event_camera_py import Decoder

topic = '/event_camera/events'
bag = BagReader('../bag', topic)
decoder = Decoder()

x_min, x_max, y_min, y_max = (0, 1280, 0, 720)
while bag.has_next():
    topic, msg, t_rec = bag.read_next()
    decoder.decode(msg)
    cd_events = decoder.get_cd_events()
    x = cd_events['x']
    y = cd_events['y']

    if (x < x_min).any() or (x >= x_max).any() or (y < y_min).any() or (y >= y_max).any():
        print(cd_events)
        raise Exception('event coordinates out of bounds')
print('no out-of-bounds coordinates found')