[ros-users] rxplot artifacts

[Stefan Kohlbrecher]

Hi Ken,

thanks for the quick explanation and code. Unfortunately the artifacts
persist despite the proposed changes. I'm not sure if they got a
little better, as that's hard to say without some longer, systematic
testing.

regards,
Stefan

2010/5/10 Ken Conley <kwc at willowgarage.com>:
> Looking at the code, my hunch is performance-related jitter inside of
> rxplot. If you have timestamped data, this isn't an issue, but if you don't
> have timestamped data, the best rxplot can do is look at the clock when it
> receives the data. Looking at the code, rxplot is taking the timestamp later
> than it should (and inside of a lock). If this lock is causing the jitter,
> it should be easy to test by changing _ros_cb() in
> rxtools/src/rxtools/rosplot.py to:
>
>     def _ros_cb(self, msg):
>         t = rospy.get_time()
>         try:
>             self.lock.acquire()
>             try:
>                 self.buff_y.append(self._get_data(msg))
>                 # #944: use message header time if present
>                 if msg.__class__._has_header:
>                     self.buff_x.append(msg.header.stamp.to_sec() -
> self.start_time)
>                 else:
>                     self.buff_x.append(t -
> self.start_time)
>                 #self.axes[index].plot(datax, buff_y)
>             except AttributeError, e:
>                 self.error = RosPlotException("Invalid topic spec [%s]:
> %s"%(self.name, str(e)))
>         finally:
>             self.lock.release()
>
> It's possible that this change won't be enough to eliminate the jitter, but
> I'm interested if it is. If this change works, we can patch ROS
> appropriately. I'll note that for non-timestamped data, jitter is always
> possible as the receipt latency can cause these artifacts.
>
>  - Ken
>
> On Mon, May 10, 2010 at 5:25 AM, Ruben Smits <ruben.smits at mech.kuleuven.be>
> wrote:
>>
>> On Monday 10 May 2010 14:15:14 Stefan Kohlbrecher wrote:
>> > Hi everyone,
>> >
>> > I am currently trying out the Orocos-ROS integration. In the process
>> > of doing so, I added a WritePort to my testing TaskContext that
>> > oscillates a floating point variable between values 0.0f and 1.0f. The
>> > task context runs at a update rate of 200 Hz. When I plot the values
>> > with rxplot, I get a large amount of artifacts, as can be see the
>> > attached file 'rxplot_jitter.png'. When pausing rxplot for a while and
>> > resuming, the data plotted for the paused period looks correct as
>> > expected (see ' rxplot_pause.png'). Is this normal behavior and can it
>> > be improved somehow?
>>
>> I suspect this is a rxplot issue ..., but I don't know the internals of
>> rxplot.
>>
>> If you look at the values using rostopic echo, do you see the same
>> artifacts?
>>
>> Ruben
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>
>
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