Grid Systems

Zone 1:  180°W - 174°W
Zone 2:  174°W - 168°W
...
Zone 10: 126°W - 120°W   ← Western US
Zone 11: 120°W - 114°W   ← California (mostly)
Zone 12: 114°W - 108°W   ← Arizona, New Mexico
...
Zone 30: 6°W - 0°        ← UK, Portugal
Zone 31: 0° - 6°E        ← France, Spain
...
Zone 60: 174°E - 180°E

# Los Angeles: 118.4°W = -118.4
Zone = floor((-118.4 + 180) / 6) + 1
Zone = floor(61.6 / 6) + 1
Zone = 10 + 1 = 11

# London: 0.1°W = -0.1
Zone = floor((-0.1 + 180) / 6) + 1
Zone = floor(179.9 / 6) + 1
Zone = 29 + 1 = 30

Los Angeles International Airport:
Zone:     11S
Easting:  368,916 m E
Northing: 3,757,142 m N

Written as: 11S 368916mE 3757142mN

UTM zones are 6° wide ≈ 668km at equator
Half width ≈ 334km
500,000m buffer ensures all eastings are positive

  11S  LA  12345  67890
  ───  ──  ─────  ─────
   │   │    │       │
   │   │    │       └── Northing (5 digits = 1m precision)
   │   │    │
   │   │    └── Easting (5 digits = 1m precision)
   │   │
   │   └── 100,000m Grid Square Identifier (GZD)
   │
   └── Grid Zone Designation (UTM Zone + Band)

Band C: 80°S - 72°S
Band D: 72°S - 64°S
...
Band N: 0° - 8°N
Band P: 8°N - 16°N
...
Band S: 32°N - 40°N      ← Southern California
Band T: 40°N - 48°N      ← Northern US
...
Band X: 72°N - 84°N      (12° tall, exception)

1. Find GZD (printed on map margin): 11S
2. Find 100km square letters: LA
3. Read EASTING (go RIGHT): 1234
4. Read NORTHING (go UP): 6789

Result: 11S LA 1234 6789

┌─────────────────────────────────┐
│  Degrees around outer edge      │  ← Bearing measurement (0-360°)
│  ┌───────────────────────────┐  │
│  │  1:25,000 scale (inner)   │  │  ← Each division = 100m at 1:25,000
│  │  1:50,000 scale (outer)   │  │  ← Each division = 100m at 1:50,000
│  │                           │  │
│  │     10 subdivisions       │  │  ← Each sub = 100m (8-digit grid)
│  │     per grid square       │  │     Estimate 10ths = 10m (10-digit)
│  └───────────────────────────┘  │
└─────────────────────────────────┘

1. Place protractor on map with correct scale facing up (1:50,000)
2. Align the protractor's right-angle corner with the SOUTHWEST corner
   of the grid square containing your point
3. Slide protractor until the vertical edge passes through your point
4. Read EASTING: the number on the horizontal scale where
   the vertical edge crosses the bottom grid line → 4 digits
5. Now slide protractor until the horizontal edge passes through your point
6. Read NORTHING: the number on the vertical scale where
   the horizontal edge crosses the left grid line → 4 digits
7. Combine: GZD + 100km letters + 4-digit easting + 4-digit northing

Example: 11S MT 8345 5712  (10m precision)

Same process as 8-digit, but estimate one additional digit
by interpolating between the finest protractor divisions:

8-digit: 11S MT 8345 5712     (10m — read directly)
10-digit: 11S MT 83452 57128  (1m — estimated interpolation)

pip install mgrs utm

#!/usr/bin/env python3
"""
MGRS/UTM Coordinate Conversion Examples
========================================

Convert between Geographic (lat/lon), UTM, and MGRS coordinate systems.

Dependencies:
    pip install mgrs utm pyproj

Usage:
    python mgrs-convert.py
"""

# =============================================================================
# Using mgrs library (simple)
# =============================================================================

def mgrs_examples():
    """MGRS library examples"""
    import mgrs

    m = mgrs.MGRS()

    # Geographic to MGRS
    lat, lon = 33.9425, -118.4081  # LAX
    mgrs_coord = m.toMGRS(lat, lon)
    print(f"LAX: {lat}, {lon}")
    print(f"  MGRS (1m): {mgrs_coord}")

    # Different precision levels
    print(f"  MGRS (10m):  {m.toMGRS(lat, lon, MGRSPrecision=4)}")
    print(f"  MGRS (100m): {m.toMGRS(lat, lon, MGRSPrecision=3)}")
    print(f"  MGRS (1km):  {m.toMGRS(lat, lon, MGRSPrecision=2)}")
    print(f"  MGRS (10km): {m.toMGRS(lat, lon, MGRSPrecision=1)}")

    # MGRS to Geographic
    lat2, lon2 = m.toLatLon(mgrs_coord)
    print(f"\n  Back to lat/lon: {lat2:.6f}, {lon2:.6f}")

    return mgrs_coord


# =============================================================================
# Using utm library
# =============================================================================

def utm_examples():
    """UTM library examples"""
    import utm

    # Geographic to UTM
    lat, lon = 33.9425, -118.4081  # LAX
    easting, northing, zone_num, zone_letter = utm.from_latlon(lat, lon)

    print(f"\nUTM Conversion:")
    print(f"  Lat/Lon: {lat}, {lon}")
    print(f"  UTM: {zone_num}{zone_letter} {easting:.2f}mE {northing:.2f}mN")

    # UTM to Geographic
    lat2, lon2 = utm.to_latlon(easting, northing, zone_num, zone_letter)
    print(f"  Back: {lat2:.6f}, {lon2:.6f}")

    return easting, northing, zone_num, zone_letter


# =============================================================================
# Using pyproj (most flexible)
# =============================================================================

def pyproj_examples():
    """PyProj examples for coordinate transformations"""
    from pyproj import CRS, Transformer

    # Define coordinate systems
    wgs84 = CRS.from_epsg(4326)  # WGS84 Geographic
    utm11n = CRS.from_epsg(32611)  # UTM Zone 11N

    # Create transformer
    to_utm = Transformer.from_crs(wgs84, utm11n, always_xy=True)
    to_geo = Transformer.from_crs(utm11n, wgs84, always_xy=True)

    # Transform
    lon, lat = -118.4081, 33.9425  # Note: lon, lat order for pyproj
    easting, northing = to_utm.transform(lon, lat)

    print(f"\nPyProj Transformation:")
    print(f"  WGS84: {lat}, {lon}")
    print(f"  UTM 11N: {easting:.2f}mE {northing:.2f}mN")

    # Reverse
    lon2, lat2 = to_geo.transform(easting, northing)
    print(f"  Back: {lat2:.6f}, {lon2:.6f}")


# =============================================================================
# Batch conversion
# =============================================================================

def batch_convert():
    """Convert multiple coordinates"""
    import mgrs

    m = mgrs.MGRS()

    locations = [
        ("LAX", 33.9425, -118.4081),
        ("JFK", 40.6413, -73.7781),
        ("ORD", 41.9742, -87.9073),
        ("DFW", 32.8998, -97.0403),
        ("McAllen", 26.2034, -98.2300),
    ]

    print("\nBatch Conversion (6-digit MGRS):")
    print("-" * 50)

    for name, lat, lon in locations:
        mgrs_6 = m.toMGRS(lat, lon, MGRSPrecision=3)
        print(f"  {name:10s}: {mgrs_6}")


# =============================================================================
# Interactive converter
# =============================================================================

def interactive_converter():
    """Simple interactive converter"""
    import mgrs

    m = mgrs.MGRS()

    print("\n" + "=" * 50)
    print("Interactive Coordinate Converter")
    print("=" * 50)

    while True:
        print("\nOptions:")
        print("  1. Lat/Lon to MGRS")
        print("  2. MGRS to Lat/Lon")
        print("  3. Exit")

        choice = input("\nChoice: ").strip()

        if choice == "1":
            try:
                lat = float(input("Latitude: "))
                lon = float(input("Longitude: "))
                precision = int(input("Precision (1-5, default 5): ") or "5")
                result = m.toMGRS(lat, lon, MGRSPrecision=precision)
                print(f"\nMGRS: {result}")
            except Exception as e:
                print(f"Error: {e}")

        elif choice == "2":
            try:
                mgrs_str = input("MGRS: ").strip().upper()
                lat, lon = m.toLatLon(mgrs_str)
                print(f"\nLat/Lon: {lat:.6f}, {lon:.6f}")
            except Exception as e:
                print(f"Error: {e}")

        elif choice == "3":
            break


# =============================================================================
# Zone calculation
# =============================================================================

def calculate_utm_zone(lon):
    """
    Calculate UTM zone from longitude

    Zone = floor((lon + 180) / 6) + 1
    """
    import math
    return math.floor((lon + 180) / 6) + 1


def latitude_band(lat):
    """
    Determine MGRS latitude band letter

    Bands are 8° tall, starting at 80°S
    Letters C-X (excluding I and O)
    """
    if lat < -80:
        return None  # South of UTM coverage
    if lat > 84:
        return None  # North of UTM coverage

    bands = "CDEFGHJKLMNPQRSTUVWX"
    index = int((lat + 80) / 8)
    if index >= len(bands):
        index = len(bands) - 1
    return bands[index]


def zone_info_demo():
    """Demonstrate zone calculations"""
    locations = [
        ("Los Angeles", 34.05, -118.24),
        ("New York", 40.71, -74.01),
        ("London", 51.51, -0.13),
        ("Tokyo", 35.68, 139.65),
        ("Sydney", -33.87, 151.21),
        ("McAllen", 26.20, -98.23),
    ]

    print("\nUTM Zone Information:")
    print("-" * 60)
    print(f"{'Location':<15} {'Lat':>8} {'Lon':>9} {'Zone':>6} {'Band':>6}")
    print("-" * 60)

    for name, lat, lon in locations:
        zone = calculate_utm_zone(lon)
        band = latitude_band(lat)
        print(f"{name:<15} {lat:>8.2f} {lon:>9.2f} {zone:>6} {band:>6}")


# =============================================================================
# Main
# =============================================================================

if __name__ == "__main__":
    print("=" * 60)
    print("MGRS/UTM COORDINATE CONVERSION EXAMPLES")
    print("=" * 60)

    try:
        mgrs_examples()
        utm_examples()
        pyproj_examples()
        batch_convert()
        zone_info_demo()
    except ImportError as e:
        print(f"\nMissing dependency: {e}")
        print("Install with: pip install mgrs utm pyproj")

    # Uncomment for interactive mode:
    # interactive_converter()

# Using proj library
echo "-118.4081 33.9425" | cs2cs +proj=longlat +datum=WGS84 +to +proj=utm +zone=11 +datum=WGS84
# Output: 368916.xx  3757142.xx

Z YE 12345 67890   (1m precision in Arctic)

Grid Reference: 11S LA 68916 57142
Zone:           11S
100km Square:   LA
Easting:        68916
Northing:       57142
Precision:      1 meter
Datum:          WGS 84