roscpp message_filters ApproximateTime API questions

edit

Regarding your first question, you want to set the setMaxIntervalDuration. As far as I understand from a quick look at the sources, a higher value for setAgePenalty makes the algorithm more sloppy for older messages (to get them out of the queue faster) and setInterMessageLowerBound allows to set a minimum delay between messages of a single input of your filter (messages arriving faster than that will be dropped).

As for the second question, you can just feed a SimpleFilter as an input to your Synchronizer:

#include <ros/ros.h>
#include <image_transport/subscriber_filter.h>
#include <message_filters/pass_through.h>
#include <message_filters/simple_filter.h>
#include <message_filters/subscriber.h>
#include <message_filters/sync_policies/approximate_time.h>
#include <sensor_msgs/Image.h>


void callback(const sensor_msgs::Image::ConstPtr& imagemessage1,
    const sensor_msgs::Image::ConstPtr& imagemessage2) {

}


int main(int argc, char ** argv) {
  ros::init(argc, argv, "test_synchronizer");
  ros::NodeHandle nodehandle;

  image_transport::ImageTransport imagetransport{nodehandle};

  image_transport::SubscriberFilter imagesubscriber1;
  imagesubscriber1.subscribe(imagetransport, "/image1", 32);

  image_transport::SubscriberFilter imagesubscriber2;
  imagesubscriber2.subscribe(imagetransport, "/image2", 32);

  message_filters::PassThrough<sensor_msgs::Image> passthrough(imagesubscriber2);
  message_filters::SimpleFilter<sensor_msgs::Image> & simplefilter = passthrough;

  using MyPolicy = message_filters::sync_policies::ApproximateTime<
      sensor_msgs::Image, sensor_msgs::Image>;
  MyPolicy mypolicy(32);
  mypolicy.setMaxIntervalDuration(ros::Duration(1.e-3));
  message_filters::Synchronizer<MyPolicy> synchronizer{
      static_cast<const MyPolicy &>(mypolicy), imagesubscriber1, passthrough};
  synchronizer.registerCallback(boost::bind(&callback, _1, _2));

  ros::spin();

  return EXIT_SUCCESS;
}