# Robot Localization Guide

## What is Localization?

Answering: "Where is my robot on the field?"

## The Grid System

12ft x 12ft field → 12x12 grid of 12" cells

```
Cell (0,0) = Red backstage
Cell (11,11) = Blue backstage
Cell (6,6) = Center
```

## Sensor Fusion

Combine three sensors:

1. **Odometry (Encoders)** - Track wheel rotation
   - Accuracy: ±1" per foot (cumulative drift)
   - Always available

2. **IMU (Gyroscope)** - Measure heading
   - Accuracy: ±2° (non-cumulative)
   - Corrects heading drift

3. **Vision (AprilTags)** - Detect position markers
   - Accuracy: ±2" (when visible)
   - Ground truth - resets drift

## Fusion Strategy

```
if vision available:
    position = vision (most accurate)
    correct odometry
elif IMU available:
    position = odometry
    heading = IMU
else:
    position = odometry only (dead reckoning)
```

## Fault Tolerance

| Sensors | Accuracy | Confidence |
|---------|----------|------------|
| All 3 | ±2" | 100% |
| Odometry + IMU | ±4" | 70% |
| Odometry only | ±12" | 40% |

System keeps working when sensors fail!

## Usage

```java
RobotLocalizer localizer = new RobotLocalizer(odometry, imu, vision);
localizer.setInitialPose(new Pose2D(12, 12, 0));

while (opModeIsActive()) {
    localizer.update();
    
    GridCell cell = localizer.getCurrentCell();
    double confidence = localizer.getConfidence();
    
    // Make decisions based on position
}
```

See README.md for full examples.