# WIA-SEMI-013 Phase 1: Data Format Specification

**Version:** 1.0  
**Date:** 2025-01-15  
**Status:** Published  

## Overview

Phase 1 defines standardized data formats for 3D image sensor specifications, depth maps, point clouds, and calibration data. These formats enable interoperability across sensors, processing libraries, and applications.

## 1. Sensor Specification Schema

### JSON Schema for 3D Sensor Metadata

```json
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "WIA-SEMI-013 Sensor Specification",
  "type": "object",
  "required": ["standard", "version", "sensor"],
  "properties": {
    "standard": {
      "type": "string",
      "const": "WIA-SEMI-013"
    },
    "version": {
      "type": "string",
      "pattern": "^\\d+\\.\\d+$"
    },
    "sensor": {
      "type": "object",
      "required": ["technology", "resolution", "frameRate", "depthRange"],
      "properties": {
        "technology": {
          "type": "string",
          "enum": ["iToF", "dToF", "structured_light", "stereo", "hybrid"]
        },
        "manufacturer": {"type": "string"},
        "model": {"type": "string"},
        "resolution": {
          "type": "object",
          "required": ["width", "height"],
          "properties": {
            "width": {"type": "integer", "minimum": 1},
            "height": {"type": "integer", "minimum": 1}
          }
        },
        "frameRate": {
          "type": "number",
          "minimum": 1,
          "maximum": 240
        },
        "depthRange": {
          "type": "object",
          "required": ["min", "max", "units"],
          "properties": {
            "min": {"type": "number", "minimum": 0},
            "max": {"type": "number"},
            "units": {"type": "string", "enum": ["meters", "millimeters"]}
          }
        },
        "accuracy": {
          "type": "object",
          "required": ["value", "units", "at_distance"],
          "properties": {
            "value": {"type": "number", "minimum": 0},
            "units": {"type": "string", "enum": ["mm", "cm", "percent"]},
            "at_distance": {"type": "number", "minimum": 0}
          }
        },
        "fieldOfView": {
          "type": "object",
          "properties": {
            "horizontal": {"type": "number", "minimum": 0, "maximum": 360},
            "vertical": {"type": "number", "minimum": 0, "maximum": 180},
            "units": {"type": "string", "enum": ["degrees", "radians"]}
          }
        },
        "wavelength": {
          "type": "integer",
          "description": "Illumination wavelength in nanometers",
          "minimum": 400,
          "maximum": 1550
        },
        "illumination": {
          "type": "string",
          "enum": ["active", "passive", "hybrid"]
        }
      }
    }
  }
}
```

### Example Sensor Specification

```json
{
  "standard": "WIA-SEMI-013",
  "version": "1.0",
  "sensor": {
    "technology": "iToF",
    "manufacturer": "Sony",
    "model": "IMX556PLR",
    "resolution": {"width": 640, "height": 480},
    "frameRate": 30,
    "depthRange": {"min": 0.2, "max": 5.0, "units": "meters"},
    "accuracy": {"value": 5, "units": "mm", "at_distance": 2.0},
    "fieldOfView": {"horizontal": 87, "vertical": 58, "units": "degrees"},
    "wavelength": 940,
    "illumination": "active"
  }
}
```

## 2. Depth Map Format

### Binary Depth Map Structure

Depth maps are encoded as 16-bit or 32-bit unsigned integers or 32-bit floating point values, with accompanying metadata.

**Header Structure (64 bytes):**

| Offset | Size | Field | Description |
|--------|------|-------|-------------|
| 0 | 4 | magic | Magic number: 0x57494133 ("WIA3") |
| 4 | 2 | version | Format version (major.minor) |
| 6 | 2 | encoding | Encoding type (0=uint16, 1=uint32, 2=float32) |
| 8 | 4 | width | Image width in pixels |
| 12 | 4 | height | Image height in pixels |
| 16 | 4 | timestamp_sec | Unix timestamp (seconds) |
| 20 | 4 | timestamp_usec | Microseconds |
| 24 | 4 | depth_scale | Scale factor (depth_mm = value × scale) |
| 28 | 4 | min_depth | Minimum valid depth (mm) |
| 32 | 4 | max_depth | Maximum valid depth (mm) |
| 36 | 4 | confidence_offset | Offset to confidence map (0 if none) |
| 40 | 24 | reserved | Reserved for future use |

**Data follows header:**
- Depth values: width × height × sizeof(encoding type)
- Confidence map (optional): width × height × 1 byte (0-255 confidence)

### Text-Based Depth Map (CSV)

For debugging and interchange, CSV format is supported:

```
WIA-SEMI-013,1.0
timestamp,2025-01-15T10:30:45.123Z
width,640
height,480
encoding,uint16
depth_scale,1.0
x,y,depth_mm,confidence
0,0,1234,255
0,1,1235,254
...
```

## 3. Point Cloud Format

### WIA Point Cloud Binary Format

Extends PCD format with WIA-specific attributes.

**Header:**
```
# .PCD v0.7 - Point Cloud Data file format
VERSION 0.7
FIELDS x y z rgb intensity confidence timestamp
SIZE 4 4 4 4 2 1 8
TYPE F F F U U U U
COUNT 1 1 1 1 1 1 1
WIDTH 307200
HEIGHT 1
VIEWPOINT 0 0 0 1 0 0 0
POINTS 307200
DATA binary
```

**Field Definitions:**
- x, y, z: 3D coordinates in meters (float32)
- rgb: Packed RGB (uint32): R=bits 16-23, G=bits 8-15, B=bits 0-7
- intensity: Infrared intensity (uint16)
- confidence: Point confidence 0-255 (uint8)
- timestamp: Microseconds since frame start (uint64)

### JSON Point Cloud (for small datasets)

```json
{
  "standard": "WIA-SEMI-013",
  "version": "1.0",
  "coordinate_system": "camera",
  "units": "meters",
  "timestamp": "2025-01-15T10:30:45.123Z",
  "points": [
    {"x": 0.123, "y": 0.456, "z": 1.234, "r": 255, "g": 128, "b": 64, "confidence": 255},
    {"x": 0.124, "y": 0.457, "z": 1.235, "r": 254, "g": 129, "b": 65, "confidence": 254}
  ]
}
```

## 4. Calibration Data Format

### Intrinsic Calibration

```json
{
  "standard": "WIA-SEMI-013",
  "version": "1.0",
  "calibration_type": "intrinsic",
  "camera_id": "sensor-001",
  "timestamp": "2025-01-15T10:30:45.123Z",
  "resolution": {"width": 640, "height": 480},
  "camera_matrix": {
    "fx": 525.0,
    "fy": 525.0,
    "cx": 319.5,
    "cy": 239.5
  },
  "distortion": {
    "model": "brown_conrady",
    "coefficients": {
      "k1": -0.123,
      "k2": 0.045,
      "p1": 0.001,
      "p2": -0.002,
      "k3": 0.012
    }
  }
}
```

### Extrinsic Calibration (Multi-Sensor)

```json
{
  "standard": "WIA-SEMI-013",
  "version": "1.0",
  "calibration_type": "extrinsic",
  "timestamp": "2025-01-15T10:30:45.123Z",
  "transforms": [
    {
      "from": "depth_camera",
      "to": "rgb_camera",
      "rotation": {
        "format": "quaternion",
        "w": 0.9999,
        "x": 0.0001,
        "y": 0.0002,
        "z": 0.0001
      },
      "translation": {
        "x": 0.025,
        "y": 0.000,
        "z": 0.001,
        "units": "meters"
      }
    }
  ]
}
```

### Temperature Compensation

```json
{
  "standard": "WIA-SEMI-013",
  "version": "1.0",
  "compensation_type": "temperature",
  "temperature_table": [
    {"temp_celsius": -20, "depth_scale": 1.002, "baseline_mm": 50.05},
    {"temp_celsius": 0, "depth_scale": 1.001, "baseline_mm": 50.02},
    {"temp_celsius": 20, "depth_scale": 1.000, "baseline_mm": 50.00},
    {"temp_celsius": 40, "depth_scale": 0.999, "baseline_mm": 49.98},
    {"temp_celsius": 60, "depth_scale": 0.998, "baseline_mm": 49.95}
  ]
}
```

## 5. Data Format Compliance

### Validation Requirements

Implementations MUST:
1. Support all required fields in sensor specification schema
2. Correctly parse binary depth map header
3. Handle depth scale factors for unit conversion
4. Support confidence maps when present
5. Correctly interpret calibration parameters

Implementations SHOULD:
1. Support optional CSV depth map format for debugging
2. Provide utilities for format conversion
3. Validate data integrity with checksums
4. Support compression (gzip, lz4) for storage/transmission

### File Extensions

- Depth maps: `.wia-depth` (binary), `.wia-depth.csv` (text)
- Point clouds: `.pcd` (standard PCD with WIA fields)
- Calibration: `.wia-calib.json`
- Sensor specs: `.wia-sensor.json`

## 6. Coordinate Systems

### Standard Coordinate Frames

**Camera Coordinate System:**
- Origin: Optical center
- X-axis: Right (image columns)
- Y-axis: Down (image rows)
- Z-axis: Forward (depth direction)

**World Coordinate System:**
- Application-defined
- Transformation from camera to world provided in calibration

### Depth Measurement Convention

Depth is measured along the Z-axis (perpendicular distance from sensor plane), NOT Euclidean distance from optical center. This convention simplifies depth-to-3D conversion.

## 7. Versioning and Extensions

### Backward Compatibility

- Version 1.x formats are backward compatible
- Parsers must ignore unknown fields
- New optional fields may be added in minor versions

### Future Extensions

- Version 2.0 may introduce:
  - Neural radiance field (NeRF) representations
  - Compressed neural point clouds
  - Multi-spectral depth data
  - Event-based depth streams

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