This is a simple application to capture ARKit motion estimation (Visual-Inertial Odometry) results on iOS devices for offline use. I want to play around with data from Apple's Visual-Inertial Odometry (VIO) solution with ARKit framework in Swift 5.0 for iPhone Xs.

For more details, see the ARKit documentation here.

The txt files are produced automatically after pressing Stop button. This Xcode project is written under Xcode Version 10.2.1 (10E1001) for iOS 12.2. It doesn't currently check for sensor availability before logging.

In the global (inertial or reference) frame in ARKit, the Y-axis (up) matches the direction of gravity as detected by the device's motion sensing hardware; that is, the vector (0,-1,0) points downward. For the Z-axis, ARKit chooses a basis vector (0,0,-1) pointing in the direction the device camera faces and perpendicular to the gravity axis. ARKit chooses a X-axis based on the Z- and Y-axes using the right hand rule. The ARKit (camera) body frame's X-axis always points along the long axis of the device (down). Y-axis points right, and the Z-axis points out the front of the device (toward the user). For more details, see the ARConfiguration WorldAlignment documentation here and here.

I have chosen the following output formats, but they are easy to modify if you find something else more convenient.

• ARKit 6-DoF Camera Pose (ARKit_camera_pose.txt): timestamp, r_11, r_12, r_13, t_x, r_21, r_22, r_23, t_y, r_31, r_32, r_33, t_z \n
• ARKit 3D Point Cloud (ARKit_point_cloud.txt): position_x, position_y, position_z, color_Y, color_Cb, color_Cr \n

Note that ARKit_camera_pose.txt contains a N x 12 table, where N is the number of frames of this sequence. Row i represents the i'th pose of the camera coordinate system via a 3x4 transformation matrix similar to KITTI dataset pose format. The matrices are stored in row aligned order (the first entries correspond to the first row), and take a point in the i'th coordinate system and project it into the first (=0th) coordinate system. Hence, the translational part (3x1 vector of column 4) corresponds to the pose of the camera coordinate system in the i'th frame with respect to the first (=0th) frame.

The ability to experiment with different algorithms to process the ARKit (VIO) motion estimation results is the reason that I created this project in the first place. I have included an example script that you can use to parse and visualize the data that comes from ARKit Data Logger. Look under the Visualization directory to check it out. You can run the script by typing the following in your terminal:

run main_script.m

Here's one of the figures produced by the Matlab script: