How to use ApproximateTime in python

asked 2013-09-19 04:43:28 -0600

whiterose
148 ●11 ●15 ●19

updated 2014-01-28 17:18:00 -0600

ngrennan
1 ●1 ●1

Hi all,

I'm trying to synchronize (approximately since the stamps of the topics are different) 4 topics.

I have looked at the ApproximateTime example here: http://answers.ros.org/question/60903/timesynchronizer-callback-problem/

But how to do it in python? I have looked at the Python API (http://docs.ros.org/api/message_filters/html/python/) for message filters, but it says nothing about approximatetime.

Thanks in advance.

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Here 10 is the size of queue and 1 is the time in sec to consider for aprox:

one = message_filters.Subscriber('robot0/sonar_0', Range)
two = message_filters.Subscriber('robot0/sonar_1', Range)
ts = message_filters.ApproximateTimeSynchronizer([one, two],10,1)
ts.registerCallback(callback)

Ananthakrishnan ( 2015-10-18 12:51:15 -0600 )edit

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4

answered 2015-04-05 12:17:33 -0600

Dan Lazewatsky
9115 ●79 ●103 ●160 http://dan.lazewatsky.com/

ApproximateTime was added for python in indigo, and is documented in the indigo version of the api docs.

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It seems that this kind of subscriber cannot be unregistered, can you confirm?

Mehdi. ( 2018-12-03 06:37:19 -0600 )edit

you can unsubscribe by iterating over each message_filter's subscription

Assuming you subscribed like this:

self.subs = [message_filters.Subscriber(topic, mtype) for topic, mtype in zip(self.topics, self.types)]
self.ts = message_filters.ApproximateTimeSynchronizer(
            self.subs,
            5,  # queue size
            0.2,
            allow_headerless=False
)  
self.ts.registerCallback(self.cb_logger)

You can unsubscribe like this:

for sub in self.subs:
            sub.sub.unregister()

ljburtz ( 2021-05-28 21:34:31 -0600 )edit

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1

answered 2017-11-25 17:04:39 -0600

jayess
6155 ●26 ●85 ●92

Just in case someone has some trouble getting going with this, here's an example:

from message_filters import ApproximateTimeSynchronizer, Subscriber

def gotimage(image, camerainfo):
    assert image.header.stamp == camerainfo.header.stamp
    print "got an Image and CameraInfo"

image_sub = Subscriber("/wide_stereo/left/image_rect_color", sensor_msgs.msg.Image)
camera_sub = Subscriber("/wide_stereo/left/camera_info", sensor_msgs.msg.CameraInfo)

ats = ApproximateTimeSynchronizer([image_sub, camera_sub], queue_size=5, slop=0.1))
ats.registerCallback(gotimage)

I adapted this from the docs.

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How to use ApproximateTime in python

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