TraceLog — Energy-Efficient Location Tracker for iOS

An iOS app that tracks your location history with minimal battery drain and minimal log entries.

How It Works

The app uses a smart threshold-based tracking algorithm:

1. Time Interval — checks your location every N seconds (default: 60s)
2. Distance Interval — creates a new log only when you've moved more than N meters (default: 100m)

Tracking Logic

Every <timeInterval>:
  Get current position
  Calculate distance from last log
  
  If distance > <distanceInterval>:
    → Close current log (set endTime)
    → Create new log (startTime, lat, lng, no endTime)
  Else:
    → Update endTime on current log (extend it)

Result: Sitting at a cafe for 2 hours = 1 log. Walking 500m with 100m threshold = 5 logs.

Tech Stack

• SwiftUI — declarative UI
• CoreLocation — background location tracking
• MapKit — map visualization
• JSON file storage — lightweight local persistence
• iOS 16+ — minimum deployment target

Energy Saving Strategy

1. Low accuracy GPS — kCLLocationAccuracyThreeKilometers (minimal GPS usage)
2. Throttled polling — only checks at configured intervals (no continuous GPS)
3. Distance-based logging — only creates logs when you actually move
4. Background mode — uses allowsBackgroundLocationUpdates with UIBackgroundModes.location
5. Auto-pause — pausesLocationUpdatesAutomatically = true

Project Structure

TraceLog/
├── Package.swift                     # SPM for core library
├── TraceLogCore/                     # Platform-independent code
│   ├── Models/LocationLog.swift      # Data model
│   └── Services/
│       ├── StorageService.swift      # JSON file persistence
│       └── SettingsService.swift     # UserDefaults settings
├── TraceLog/                         # iOS app (requires Xcode)
│   ├── TraceLogApp.swift             # App entry point + TabView
│   ├── Models/LocationLog.swift      # (same as core)
│   ├── Services/
│   │   ├── LocationTracker.swift     # CoreLocation + tracking logic
│   │   ├── StorageService.swift      # (same as core)
│   │   └── SettingsService.swift     # (same as core)
│   ├── Views/
│   │   ├── HomeView.swift            # Map + start/stop toggle
│   │   ├── HistoryView.swift         # Logs grouped by date
│   │   └── SettingsView.swift        # Interval pickers
│   ├── Assets.xcassets/
│   └── Info.plist                    # Permissions + background modes

Build

Core Library (command line)

swift build

GitHub Actions (automatic)

Every push to main triggers a build. No setup needed — just push.

git add .
git commit -m "your changes"
git push

Check build status: Actions tab on your GitHub repo page.

Free tier: 2,000 min/month (macOS = 10x multiplier → ~200 real minutes, ~40-60 builds/month).

Local (requires Xcode)

1. brew install xcodegen
2. xcodegen generate (creates .xcodeproj)
3. Open TraceLog.xcodeproj in Xcode
4. Select your iPhone → Build & Run

Usage

1. Grant location permission — "Always Allow" for background tracking
2. Tap Start Tracking — begins monitoring your location
3. View history — see past logs grouped by date, tap to view on map
4. Configure settings — adjust time/distance intervals to balance accuracy vs battery

Permissions

The app requires:

• Location When In Use — basic tracking while app is open
• Location Always — background tracking when app is closed
• Background Mode: Location — enables tracking in background

TraceLog