Mobile Sensor Logger

Android app that records camera images and inertial data for 3D reconstruction on a workstation.

• Captures at the device's largest YUV_420_888 size — 4080x3060 on a Galaxy S25 Ultra
• Writes the sharpest frame of each stretch of movement, not every frame
• Records accelerometer and gyroscope on the same clock as the images
• Computes no pose on the device

C++ throughout, against the Camera2 NDK, with no application Java or Kotlin. GameActivity hosts it.

Building and running

./gradlew assembleDebug
adb install -r app/build/outputs/apk/debug/app-debug.apk

Needs the Android SDK, NDK and CMake; versions are pinned in app/build.gradle.kts and the wrapper. Built with JDK 21. There is no emulator path — the capture path is a real camera.

Button	Action
Volume down	start and stop recording
Volume up	show or hide the camera
The lock button	pin the current metered exposure so recording starts on it, wherever the phone is pointed when the key is pressed; refused while recording
The retention button	toggle sharpest / all; refused while recording
The lens button	next rear lens; refused while recording
The PRO button	open the panel for shutter, fps, mains, shift and residual — see below; refused while recording
The sessions button	view saved sessions, and delete them individually; refused while recording
Home	leave, closing the session cleanly

The PRO panel has one row per setting that cycles its value on tap, the same way retention and lens already do, plus a RESET button beside CLOSE that puts all five back to their defaults at once. Unlike retention and lens, a change here is also written back to capture.conf (see docs/settings.md), so it survives the app being killed rather than reverting to whatever the file said when this session opened.

Nothing that could lose a capture sits behind a touch. Deleting a session is: tap DEL next to it, then tap the same button again to confirm — one tap never deletes anything, and there is no delete-all.

Pulling and clearing a device:

adb pull /sdcard/Android/data/com.sensor.logger/files/sessions data/
adb shell run-as com.sensor.logger \
  rm -rf /sdcard/Android/data/com.sensor.logger/files/sessions

The second needs run-as; a plain rm is refused under scoped storage. For removing one session rather than all of them, the sessions button is usually easier than pulling and re-pushing.

On screen

The camera is not drawn unless volume up asks for it. The numbers are what the screen is for during a capture; the picture is for aiming, which happens between captures more than during one.

REC 0:57   36 MIN LEFT      elapsed, and how long the free space lasts
153 KEPT / 1696 SEEN        frames written against frames scored
2.9GB USED 111.0GB FREE
SHIFT 2/12  DIFF 4/6        movement against the thresholds that keep a frame
4080X3060
1/30 ISO247 0.91M           shutter, sensitivity, focus — held or still moving
DROP 0 NOIMG 0 IMU 36K      drops should be zero
BATT 78% 32.1C              shown whether or not anything is recording

[ LOCK ]
[ RETENTION SHARP ]
[ ULTRAWIDE 2.2MM ]
[ PRO ]
[ SESSIONS ]

MIN LEFT is measured from the rate this capture is actually filling the disk, not estimated in advance. The lock button reads PINNED once tapped, and brighter amber, so a stale pin is obvious rather than only readable from the label. The lens button only appears on a phone with more than one rear camera; the rest are always there, ordered by how often each gets touched around a recording — lock nearly every take, retention and lens less often, PRO rarer still since it is tuned once for a scene rather than every take, and sessions is an occasional housekeeping visit that sits furthest from a thumb reaching for the others in a hurry.

Tested on

Hardware profiles and camera parameters for tested devices (Galaxy S25 Ultra, Galaxy Z Flip4) are documented in docs/devices.md.

Documentation

Document	Description
docs/output-format.md	what a session leaves on disk, and how to read it
docs/settings.md	capture.conf, and what each choice costs
docs/devices.md	hardware profiles and parameters for tested devices
docs/calibration-guide.md	what to do when a device doesn't publish camera calibration
docs/adr/	why it is built this way