access message filters cache data in python

edit

Hey Austin

Thank you very much for your reply. I will report the issue for sure. At the mean time I have implemented the C++ version of the message filters cache. it looks find except that I have some packet lost in between. I am publishing a message with header and there I have 128Hz frequency but when I am reading cache with :

1. start_time = ros::Time::now();
2. cache.getInterval(start_time - ros::Duration(1), start_time).size()

The vector has size of 107-115. When I only subscribe and print it also seems fine. Are there any packet lost of I just need to increase the duration to get full cycle that i publish ?

ROS is designed to drop packets when a topic is saturated, so it's quite possible that it's losing a few. The only way to really know is to analyze the message sequence numbers to see if any messages are missing.

I did so and it keep losing around 20 packets that are important for me.. actually I am trying to make emokit signals in available in ros... I can publish the message but the points is each message contains one packet and the sampling frequency for the device is 128Hz. Publisher does not lose any packet, also the subscriber.

But i need to queue 10 second of these packets and lose a service ros service to access the desired interval. Do you have any suggestion about how to do this ?

Boost::circularBuffer is the thing i am trying to use for queuing messages at moment .

You may want to try increasing the publisher and subscriber queue sizes to see if that helps prevent dropping messages.

Thanks for the reply I did so and now I am publishing the packets getting them from cache .... the code is looks like this now and I am using a service to read from the new topic... I hope this code is optimal ?

`

message_filters::Cache<bci_eeg_msgs::EegPacket>
eeg_packet_cache;
bci_eeg_msgs::EegPacketBuffer
eeg_packet_buffer; ros::Publisher
eeg_packet_buffer_pub ;

void some_function (const
bci_eeg_msgs::EegPacket::ConstPtr
&msg) {
    eeg_packet_cache.add(msg);

    std::vector<bci_eeg_msgs::EegPacket::ConstPtr>
eeg_cache_vector =
           eeg_packet_cache.getInterval(eeg_packet_cache.getOldestTime(),
eeg_packet_cache.getLatestTime());
       for(uint i = 0; i < eeg_cache_vector.size(); ++i){   
eeg_packet_buffer.data.push_back(*eeg_cache_vector[i]);
}   
eeg_packet_buffer_pub.publish(eeg_packet_buffer);
     }

int main(int argc, char **argv) {  
ros::init(argc, argv,
"caching_example");  
ros::NodeHandle nh;  
eeg_packet_cache.setCacheSize(128*5);
ros::Subscriber sub =
nh.subscribe("/eeg_signal_packet",
256 , some_function);  
eeg_packet_buffer_pub = 
      nh.advertise<bci_eeg_msgs::EegPacketBuffer>("/eeg_packet_buffer",1);
ros::spin();   return 0; }`

@raminzohouri: I think it would be better if you update your original question. The comment area is just that: for short comments. Seeing as your original question was answered by @ahendrix though, you might want to create a new one (for your problem with msg loss).