Kalibr Targets

1. Order the exact sizes that match your file's artboards; use the keyboard to add decimals if needed.
2. Upload your own custom files, vector PDF files are preferred for optimal print results.
3. Full-scale files are required to avoid the files being scaled up or down to fit the image on the board's order size.
4. During the proofing process, always double-check and compare the file size to each board order size (Foamcoreprint.com is not responsible for artwork scaling if the incorrect board sizes are ordered and proofs are approved incorrectly).
5. If you have questions about the artwork uploaded to an order; please call, email, or start a live chat before sending the art files to print. Production will begin within 10 mins of approval of artwork. Once production begins, we can not remove approved art files from the production line.

Kalibr uses the calibration software, and it is ideal for IMU and multi-camera calibration.

The calibrations are based on the AprilTag coded markers. They enable the recording of information from the edges of the images, which helps in the robust and accurate lens parameters' determination.

The coding of feature points also helps in stereo calibration in which corners can be partly non-visible.

Additionally, the software comes with advanced calibration routines that are ideal for autonomous vehicle calibration and drones.

They support three targets which include:

• Aprilgrid
• Checkerboard
• Circle grid

Aprilgrid is the most preferred one as it comes with many benefits, including:

• You can use the partially visible calibration boards
• The pose of the target is fully resolved (no flips)

You'll use the YAML configuration files offered to the calibration software to configure the targets.

Aprilgrid is the recommended choice as it simplifies data collection significantly.

With Aprilgrid, the targets are partially visible, and you can detect them without a challenge.

You can download Aprilgrids from the download page, or you can also create the custom grids.

When collecting the calibration data sets, you should make sure to hide all external Apriltags.

The software uses the Apriltag implementation of M. Kaess for tag extraction.

Most calibration targets have an aluminum or LDPE composite construction, which offers a perfect stiffness and flatness but is also lightweight.

Additionally, the composite material is corrosion-resistant, and it also offers good thermal stability.

You use the direct UV (Ultra-Violet) printing process to transfer the patterns to the composite material. This results in a durable matte finish.

The ultra-violet printing process is ideal for machine vision applications where you require accuracy, excellent optical performance, and physical robustness.

Circle grids are also a common and famous calibration target design based on circles. It can be white circles on a dark background or dark/black circles on a white background.

If you are using image processing terms, you can detect circles as blobs in the image. You can apply simple conditions on the binary blob regions such as convexity, area, circularity, etc., to get rid of bad feature candidates.

After getting the best candidates, you use the regular structure of features to identify and filter the pattern. You can enjoy high accuracy in the determination of circles as you can use all the pixels in the periphery of circles, which decreases the influence of image noise.

These targets are based on the traditional checkerboards, and they can use the same algorithms.

They have three circles at the center, enabling absolute referencing even with partial views of the checkerboard.

• You should ensure the calibration target is as flat as possible. It will be best to glue it to a rigid plate such as acrylic glass or aluminum
• It will be best to have a white border around the calibration target, or you will have challenges with detection in various lighting conditions
• Various printers will scale the calibration target while printing. As such, it will be best to remeasure all the essential sizes and also adjust the target configuration

There are two sources available for the toolbox, including:

It is the fastest way to have the toolbox running. You get all dependencies on the package, and you don't require external dependencies. The CDE package doesn't include a calibration validator or camera focus as they require ROS installation.

The source depends on the installation of catkin workspace and ROS indigo. All tools are available with this source, and it runs faster than the CDE package.

CDE package is an excellent option if you wish to remove the need for installing ROS.

Ensure you install the most recent package. You can run the tools from the CDE package folder directly.

To use the building from the source option, first, ensure you install the ROS indigo.

Example installation on Ubuntu includes:

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu trusty main" > /etc/apt/sources.list.d/ros-latest.list'

After that, install the dependencies and come up with a catkin workspace.

Clone the source repo into the catkin workspace src folder and then use the Release configuration to build the code.

You can also use the Docker image by Stereo labs to run the software.

You can check the image topic Hz by running the camera using the following command:

roslaunch realsense2_camera rs_camera . launch

rostopic Hz / camera/color/image_raw

Kalibr is one type of calibration software (others being PhotoModeler and Halcon) that is ideal for solving various challenges, including rolling shutter camera calibration, visual-inertia calibration, and multiple-camera calibration.