MARS Logger for iOS

MARS Logger records synchronized camera, ARKit pose, camera calibration, and Core Motion data on an iPhone. The primary MarsLogger target is now a native SwiftUI application built around one authoritative ARSession.

The original Objective-C RosyWriter sources and alternate render targets remain in the repository for reproducibility and comparison. They are no longer the source files compiled by the primary target.

What the Swift application records

Each capture is stored under Documents/MarsLogger/<ISO-8601 timestamp>/:

camera.mov   H.264 frames sourced from ARFrame.capturedImage
frames.csv   pose, intrinsics, resolution, tracking state, and timestamps
imu.csv      acceleration, rotation rate, gravity, attitude, and timestamps

ARKit frame timestamps and Core Motion timestamps both use device-uptime clock semantics. Each CSV also includes an estimated Unix timestamp using the boot-time offset measured when the writer is created.

Why ARKit owns camera capture

The Swift migration does not run an AVCaptureSession beside ARKit. ARKit owns the camera, and video is encoded directly from each ARFrame.capturedImage. That keeps image, camera transform, intrinsics, tracking state, and frame time attached to the same source frame while avoiding camera-session contention.

Run

Requirements:

• Xcode 16 or later
• iOS 15 or later
• A physical ARKit-capable iPhone or iPad

Open MarsLogger.xcodeproj, select the MarsLoggerOpenGL scheme, choose your development team and a physical device, then run.

1. Grant camera and motion permission.
2. Wait for tracking state to become normal.
3. Tap Record.
4. Move through the capture area.
5. Tap Stop.
6. Tap Share Last Capture to export the video and both CSV files.

CSV conventions

• Matrices are written in the column-major order returned by simd/ARKit.
• Translation is in meters in ARKit's right-handed world coordinate system.
• Rotation rate is radians per second.
• User acceleration and gravity use Core Motion's g units.
• Locale-independent decimal formatting is used.
• Tracking limitations are recorded explicitly instead of silently dropping frames.

Privacy

Captures remain in the app's Documents directory until the user exports or deletes them. The application contains no account, analytics, network upload, or background transmission path.

Legacy implementation

The Classes/, Resources/, and main.m paths contain the historical Objective-C implementation derived from Apple's RosyWriter sample. The CPU, Core Image, and OpenCV schemes remain legacy comparison targets. New work should target the Swift MarsLoggerOpenGL application unless a maintainer decides to remove or consolidate those schemes separately.

License

GPL-3.0. See LICENSE and the original Apple sample terms in LICENSE.txt.