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Visual-Inertial-Synchronization-Hardware

★ 90 Open GitHub ↗

This project aims to hardware-synchronize camera and IMU so that both use the same (millisecond precise) time base.

// repository documentation

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# Visual-Inertial-Synchronization-Hardware

#### Authors: [Xinliang Zhong](www.xinliang-zhong.com)(xinliangzhong@foxmail.com), [Xu Chen](https://github.com/xuchen27)(chenxu@bit.edu.cn)

## 1.Description
This projects aims to hardware-synchronize camera and IMU so that both use the same (millisecond precise) time base. We have tested the code in Ubuntu16.04 (ROS Kinetic).

![hardware](https://raw.githubusercontent.com/TurtleZhong/Visual-Inertial-Synchronization-Hardware/master/mpu6050_serial_to_imu/imgs/hardware_system.png)

The Arduino will calculate precise (microsecond) timestamps for each IMU measurement (200 Hz). At certain timestamps (20 Hz), it will trigger the camera (via the trigger line) to capture a new image. Timestamp and triggerCounter data will be sent to the PC (IMU node). The IMU node will receive IMU data from the Arduino and publish the time data via a new ROS TimeReference message (topic /imu/trigger_time). The camera node will subscribe to this time data to reconstruct precise time for each camera image. So, the message flow will be like this:

```
IMU –> Arduino –> PC (ROS IMU node) –> ROS camera node
```

## 2.Requirements

### 2.1 Hardware
In our implementation, we choose **[bumblebee2](https://www.ptgrey.com/bumblebee2-firewire-stereo-vision-camera-systems)** which support **externel trigger **as the stereo visual sensor and **[mpu6050](https://www.invensense.com/products/motion-tracking/6-axis/mpu-6050/)** as the inertial sensor. Below are the details:

| Hardware | Visual Sensor | IMU sensor | Embedded devices |
|--------|--------|--------|--------|
| Name | Bumblebee2 1394a | MPU6050 |Arduino Mega 2560 |
| Description | ![bumblebee2](https://raw.githubusercontent.com/TurtleZhong/Visual-Inertial-Synchronization-Hardware/master/mpu6050_serial_to_imu/imgs/bumblebee2.jpeg) | ![bumblebee2](https://raw.githubusercontent.com/TurtleZhong/Visual-Inertial-Synchronization-Hardware/master/mpu6050_serial_to_imu/imgs/mpu6050.jpeg) |![bumblebee2](https://raw.githubusercontent.com/TurtleZhong/Visual-Inertial-Synchronization-Hardware/master/mpu6050_serial_to_imu/imgs/mega.png) |

The wiring diagram of the whole system is shown in figure.
*	Part1: mpu6050 to Arduino
*	Part2: Camera
*	Part3: Whole System

### 2.2 Software
*	ROS Kinetic
*	sudo apt-get install ros-kinetic-serial

## 3.Data Structure
The Arduino will send useful information to the imu node via usb.The structure like this:

|Description|'$'|0x03|quaternion|gyro|acc|temperature|timestamps|triggures|'\r'|'\n'|
|-|--------|--------|-|-|-|-|-|-|-|-|
|Bytes|1|1|8|6|6|2|4|4|1|1|

After we send the data to imu_node, we parse the data and reconstruct it as the imu messages:

* **`imu/data`** ([sensor_msgs::Imu])

The measured accelerometer, gyro and orientation values.

* **`/imu/trigger_time`** ([sensor_msgs::TimeReference])

The timestamp of image and image sequence.

* **`imu/temperature`** ([sensor_msgs::Temperature])

The measured temperature in degrees Celsius.

So far, you can use mpu6050_serial_to_imu_node to test the imu data:

```bash
roslaunch mpu6050_serial_to_imu mpu6050.launch
```

Visual-Inertial-Synchronization-Hardware

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