---

name: chart-georef description: Georeferencing approach plates and airport diagrams. Use when adding location awareness to FAA d-TPP charts, creating moving map overlays for approach plates, or correlating CIFP procedures to chart images.

Chart Georeferencing

Overview

Add geographic coordinate references to approach plates and airport diagrams for moving map display.

Process

1. Extract Control Points - Identify reference points on the chart
2. Calculate Transform - Compute affine transformation matrix
3. Apply Georef - Transform pixel coordinates to lat/lon
4. Validate Accuracy - Verify against known points

Quick Start

Extract Control Points

Copyfrom extract_control_points import extract_points

# Automatically find control points
points = extract_points('KLAX_ILS_25L.pdf')
# Returns: [(pixel_x, pixel_y, lat, lon), ...]

Calculate Transformation

Copyfrom calculate_transform import PlateGeoreference

# From 3+ control points
georef = PlateGeoreference.from_control_points([
    (100, 200, 33.9425, -118.4081),  # Airport reference point
    (500, 150, 33.9500, -118.3800),  # Navaid
    (300, 600, 33.9200, -118.4200),  # Fix
])

# Transform pixel to lat/lon
lat, lon = georef.pixel_to_latlon(350, 400)

Validate Accuracy

Copyfrom validate_accuracy import validate_georef

results = validate_georef(
    georef=georef,
    known_points=known_points,
    max_error_nm=0.1
)
print(f"RMS Error: {results['rms_error_nm']:.3f} nm")

Control Point Types

References

• Affine transformation: references/affine_transform.md
• Control point types: references/control_point_types.md
• CIFP correlation: references/cifp_correlation.md
• Accuracy standards: references/accuracy_standards.md

Scripts