event_camera_codecs

This repository holds code for decoding event_camera_msgs. It builds under both ROS1 and ROS2. You can use this decoder from python via the event_camera_py repository.

Supported platforms

Currently tested on:

• ROS1: Ubuntu 20.04 on Noetic
• ROS2: Ubuntu 22.04 on Humble, Iron, Rolling

How to build

Set the following shell variables:

repo=event_camera_codecs
url=https://github.com/ros-event-camera/${repo}.git

and follow the instructions here

configure and build on ROS1:

catkin config -DCMAKE_BUILD_TYPE=RelWithDebInfo  # (optionally add -DCMAKE_EXPORT_COMPILE_COMMANDS=1)
catkin build

configure and build on ROS2:

cd ~/ws
colcon build --symlink-install --cmake-args -DCMAKE_BUILD_TYPE=RelWithDebInfo  # (optionally add -DCMAKE_EXPORT_COMPILE_COMMANDS=1)

To also build the unit tests, add the cmake argument -DEVENT_CAMERA_CODECS_BUILD_TESTS=ON.

API example

```cpp #include <event_camera_codecs/decoder.h> #include <event_camera_codecs/decoder_factory.h>

using event_camera_codecs::EventPacket;

class MyProcessor : public event_camera_codecs::EventProcessor { public: inline void eventCD(uint64_t, uint16_t ex, uint16_t ey, uint8_t polarity) override { // do useful stuff here } void eventExtTrigger(uint64_t, uint8_t, uint8_t) override {} void finished() override{}; // called after no more events decoded in this packet void rawData(const char *, size_t) override{}; // passthrough of raw data };

MyProcessor processor;

// the decoder factory method is templated on the event processor // to permit inlining of methods like eventCD() above.

event_camera_codecs::DecoderFactory<EventPacket, MyProcessor> decoderFactory;

// to get callbacks into MyProcessor, feed the message buffer // into the decoder like so

void eventMsg(const event_camera_codecs::EventPacketConstSharedPtr & msg) { // will create a new decoder on first call, from then on returns existing one auto decoder = decoderFactory.getInstance(msg); if (!decoder) { // msg->encoding was invalid return; } // the decode() will trigger callbacks to processor decoder->decode(msg, &processor); }

/* To synchronize with frame based sensors it is useful to play back until a frame boundary is reached. The interface decodeUntil() is provided for this purpose. Do NOT use decode() and decodeUntil() on the same decoder! In the sample code belowframeTimes is an ordered queue of frame times. */

void eventMsg2(const event_camera_codecs::EventPacketConstSharedPtr & msg) { auto decoder = decoderFactory.getInstance(msg); uint64_t nextTime{0}; // The loop will exit when all events in msg have been processed // or there are no more frame times available decoder->setTimeBase(msg->time_base); while (!frameTimes.empty() && decoder->decodeUntil(msg, &processor, frameTimes.front(), &nextTime)) { // use loop in case multiple frames fit inbetween two events while (!frameTimes.empty() && frameTimes.front() <= nextTime) { // processFrameHere() frameTimes.pop(); } }

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