ExactTime policy: how it works? How to choose epsilon? [closed]

asked 2014-09-10 03:42:10 -0500

mark_vision
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In this description it is said that ApproximateTime works without any epsilon to set. So I infer that ExactTime need an epsilon to be set to allow slightly different timestamps to match. But I found no methods to do that in the API reference. Ho can I set them? I already tried ApproximateTime but it's too slow. An

Closed for the following reason the question is answered, right answer was accepted by mark_vision
close date 2014-09-10 11:25:56.586185

answered 2014-09-10 05:00:01 -0500

ahendrix

47576 ●179 ●367 ●662 http://namniart.com/

The ExactTime synchronizer requires that the message timestamps match exactly; there is no epsilon. This is possible because ROS timestamps are fixed-precision, not floating point.

If the exact and approximate and exact synchronizer policies don't work for your application, it should be possible to implement your own synchronization policy by inheriting from the message_filters::PolicyBase class template.

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Before doing that I tried this simple trick to see if ExactTime is faster: I used two subscribers that take from the same topic. This means that they will have the same time-stamp by definition. Well, the input is 14 Hz but I only get 6 Hz, so there's no chance that I can reach more with a custom

mark_vision ( 2014-09-10 07:28:19 -0500 )edit

policy that for instance allows an offset of 100 ns. So...how can I get it faster? I tried to reduce the queue to one but it gets even worse. Is it normal that the filter halves the frequency? Is it because the input is very big (PointCloud2)?

mark_vision ( 2014-09-10 07:30:24 -0500 )edit

Found the flaw. They gave me a corrupted Bag, one of the two topics was at 6 Hz. Question solved.

mark_vision ( 2014-09-10 11:25:33 -0500 )edit

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ExactTime policy: how it works? How to choose epsilon? [closed]

Closed for the following reason the question is answered, right answer was accepted by mark_vision
close date 2014-09-10 11:25:56.586185

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ExactTime policy: how it works? How to choose epsilon? [closed] edit

Closed for the following reason the question is answered, right answer was accepted by mark_vision close date 2014-09-10 11:25:56.586185

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ExactTime policy: how it works? How to choose epsilon? [closed]

Closed for the following reason the question is answered, right answer was accepted by mark_vision
close date 2014-09-10 11:25:56.586185