This simple application records values coming from an iOS device's CoreMotion sensors (accelerometer, gyroscope, and magnetometer) and makes them available in a CSV formatted file in iCloud or iTunes (RIP). My goal in creating this app was to allow for quick data collection while moving with the device. After collection, the data would be processed with Apple's CoreML application for learning and (hopefully) future categorization of activity based on sensor data.
The code works with Xcode 11 and Swift 5. Should work without problems with earlier versions, but the current storyboard layout uses iOS 13 features. There would be minimal adjustments to make it work on older iOS versions.
There are three views in this app:
- Main recording view with a Start/Stop button and movement buttons.
- Recording history list that shows active and past event recordings. Swipe on a row to (re)upload, share, or delete the recording.
- Settings view reachable from the main recording view via the gear icon.
Press Start to begin a new recording of sensor data. Move around.
When done, press Stop to quit data collect. If iCloud is enabled for the device, the app will attempt to copy the file to your iCloud Drive, in a folder called MotionCollector.
Each recording fie is named with the date/time when the recording started. They all have the suffix .csv so you should be able to open them in whatever editor or spreadsheet application you wish.
Drag right on a recording to see controls for uploading and sharing the recorded values as a CSV file. Drag left to reveal a trash can to touch to remove the recording.
You can control which components are samples for data capture, the rate of data capture, and if the files are stored in an iCloud folder.
The file consists of lines of comma-separated values (CSV). The first line contains column labels for the rest of the rows.
- Source -- indicates which sensor emitted the data.
- A = accelerometer
- D = device motion
- G = gyroscope
- M = magnetometer (compass)
- Label -- indicates the current user activity, W = walking, T = turning
- When -- timestamp of the record. These are given as number of seconds since 00:00:00 UTC 1 January, 1970 or the Unix epoch, though the resolution of the values is much finer than a second.
All sensors emit at minimum three values, one for each of the 3 axis that define the orientation of the device in the real world.
- X -- X axis sensor value
- Y -- Y axis sensor value
- Z -- Z axis sensor value
For the device motion records (Source == 'D'), there are 9 values instead of 3.
- X -- X axis rotation rate
- Y -- Y axis rotation rate
- Z -- Z axis rotation rate
- UA_X -- X axis user acceleration
- UA_Y -- Y axis user acceleration
- UA_Z -- Z axis user acceleration
- Pitch -- device rotation about the X axis
- Roll -- device rotation about the Y axis
- Yaw -- device rotation about the Z axis
See this page for a discussion of the pitch, roll, and yaw values and how they relate to the device.
