# IntelRealSense D435i Calibration

### Installing Kalibr

#### Building Kalibr from Source

1. Install the necessary dependencies:

   ```bash
   sudo apt-get install -y git wget autoconf automake nano libeigen3-dev libboost-all-dev libsuitesparse-dev doxygen libopencv-dev libpoco-dev libtbb-dev libblas-dev liblapack-dev libv4l-dev python3-dev python3-pip python3-scipy python3-matplotlib ipython3 python3-wxgtk4.0 python3-tk python3-igraph python3-pyx
   ```
2. Create and configure a workspace:

   ```bash
   mkdir -p ~/kalibr_workspace/src
   cd ~/kalibr_workspace
   export ROS1_DISTRO=noetic # Replace 'noetic' with your ROS version
   source /opt/ros/$ROS1_DISTRO/setup.bash
   catkin init
   catkin config --extend /opt/ros/$ROS1_DISTRO
   catkin config --cmake-args -DCMAKE_BUILD_TYPE=Release
   ```
3. Clone the Kalibr project and build it:

   ```bash
   cd ~/kalibr_workspace/src
   git clone https://github.com/ethz-asl/kalibr.git
   cd ~/kalibr_workspace/
   catkin build -DCMAKE_BUILD_TYPE=Release -j4
   ```

   Source the workspace setup:

   ```bash
   source ~/kalibr_workspace/devel/setup.bash
   ```

### Recording a Rosbag

To record a rosbag, follow these steps:

1. Start ROS using the command:

   ```bash
   roscore
   ```
2. Install the IntelRealSense ROS package for your ROS distribution:

   ```bash
   sudo apt-get install ros-$ROS_DISTRO-realsense2-camera
   source devel/setup.bash
   ```
3. Launch the camera node using:

   ```bash
   roslaunch realsense2_camera rs_camera.launch
   ```
4. Check that camera topics are listed with:

   ```bash
   rostopic list
   ```

   You should see topics such as `camera/color/image_raw`.
5. Record a rosbag from all topics:

   ```bash
   rosbag record -a
   ```

   Press Ctrl+C to stop recording. The rosbag will be saved in the current directory.

   **Important points during recording:**

   * Excite all IMU axes (rotation and translation).
   * Avoid shocks, especially at the beginning and end of recording.
   * Maintain low motion blur through low shutter times and good illumination.
   * Ensure timestamps have low jitter and are synchronized.
6. Check the rosbag info and play it using:

   ```bash
   rosbag info
   rosbag play
   ```

### Calibrating the Camera Using AprilGrid

1. Ensure the AprilGrid details are specified in a `.yaml` file.
2. To calibrate the camera, run the following command in the directory containing the `.yaml` file and rosbag:

   ```bash
   rosrun kalibr kalibr_calibrate_cameras --target [name of .yaml file] --models [camera/distortion models to be fitted] --topics [name of topic where image from camera is being published] --bag [path to rosbag] --bag-freq 10.0 --show-extraction
   ```

   **Notes:**

   * The camera distortion model used should be `pinhole-radtan`.
   * The `--show-extraction` flag shows the calibration alongside the feed.
   * The `--bag-freq 10.0` sets the playback frequency of the rosbag to 10 Hz during calibration.

The results of the calibration process will be saved in a PDF and the matrix parameters will be stored in a `.yaml` file in the same directory.


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