FreeDATA/freedata_server/maidenhead.py

import math
import random


def haversine(lat1, lon1, lat2, lon2):
    """
    Calculate the great circle distance in kilometers between two points
    on the Earth (specified in decimal degrees).

    Parameters:
    lat1, lon1: Latitude and longitude of point 1.
    lat2, lon2: Latitude and longitude of point 2.

    Returns:
    float: Distance between the two points in kilometers.
    """
    # Radius of the Earth in kilometers. Use 3956 for miles
    R = 6371.0

    # Convert latitude and longitude from degrees to radians
    lat1 = math.radians(lat1)
    lon1 = math.radians(lon1)
    lat2 = math.radians(lat2)
    lon2 = math.radians(lon2)

    # Difference in coordinates
    dlon = lon2 - lon1
    dlat = lat2 - lat1

    # Haversine formula
    a = math.sin(dlat / 2) ** 2 + math.cos(lat1) * math.cos(lat2) * math.sin(dlon / 2) ** 2
    c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a))

    distance = R * c

    return distance


def maidenhead_to_latlon(grid_square):
    """
    Convert a Maidenhead locator to latitude and longitude coordinates.
    The output coordinates represent the southwestern corner of the grid square.

    Parameters:
    grid_square (str): The Maidenhead locator.

    Returns:
    tuple: A tuple containing the latitude and longitude (in that order) of the grid square's center.
    """

    grid_square = generate_full_maidenhead(grid_square)

    grid_square = grid_square.upper()
    lon = -180 + (ord(grid_square[0]) - ord("A")) * 20
    lat = -90 + (ord(grid_square[1]) - ord("A")) * 10
    lon += int(grid_square[2]) * 2
    lat += int(grid_square[3])

    if len(grid_square) >= 6:
        lon += (ord(grid_square[4]) - ord("A")) * (5 / 60)
        lat += (ord(grid_square[5]) - ord("A")) * (2.5 / 60)

    # not needed now as we always have 6 digits
    if len(grid_square) == 8:
        lon += int(grid_square[6]) * (5 / 600)
        lat += int(grid_square[7]) * (2.5 / 600)

    # Adjust to the center of the grid square
    # not needed now as we always have 6 digits
    if len(grid_square) <= 4:
        lon += 1
        lat += 0.5
    elif len(grid_square) == 6:
        lon += 2.5 / 60
        lat += 1.25 / 60
    else:
        lon += 2.5 / 600
        lat += 1.25 / 600

    return lat, lon


def latlon_to_maidenhead(lat, lon, precision=6):
    """
    Convert latitude and longitude to a Maidenhead locator.

    Parameters:
    lat (float): Latitude in degrees.
    lon (float): Longitude in degrees.
    precision (int): Number of characters in the locator (4, 6 or 8). Default 6.

    Returns:
    str: Maidenhead locator string.
    """

    lon += 180
    lat += 90

    A = ord("A")
    _a = ord("a")

    lon_field = int(lon // 20)
    lat_field = int(lat // 10)

    lon_square = int((lon % 20) // 2)
    lat_square = int((lat % 10) // 1)

    lon_subsquare = int(((lon % 2) / 2) * 24)
    lat_subsquare = int(((lat % 1) / 1) * 24)

    locator = f"{chr(A + lon_field)}{chr(A + lat_field)}{lon_square}{lat_square}{chr(A + lon_subsquare)}{chr(A + lat_subsquare)}"

    if precision == 4:
        return locator[:4]
    elif precision == 8:
        lon_ext = int((((lon % (1 / 12)) / (1 / 12)) * 10))
        lat_ext = int((((lat % (1 / 24)) / (1 / 24)) * 10))
        return locator + f"{lon_ext}{lat_ext}"
    else:
        return locator[:6]


def distance_between_locators(locator1, locator2):
    """
    Calculate the distance between two Maidenhead locators and return the result as a dictionary.

    Parameters:
    locator1 (str): The first Maidenhead locator.
    locator2 (str): The second Maidenhead locator.

    Returns:
    dict: A dictionary containing the distances in kilometers and miles.
    """
    lat1, lon1 = maidenhead_to_latlon(locator1)
    lat2, lon2 = maidenhead_to_latlon(locator2)
    km = haversine(lat1, lon1, lat2, lon2)
    miles = km * 0.621371
    return {"kilometers": km, "miles": miles}


def generate_full_maidenhead(grid_square):
    """
    Convert a Maidenhead locator of 2 or 4 characters to a 6-character locator
    by generating random characters for the missing positions, while ensuring the correct format:
    1-2: Uppercase letters (A-R)
    3-4: Digits (0-9)
    5-6: Lowercase letters (a-r)

    Parameters:
    grid_square (str): A 2, 4, or 6 character Maidenhead locator.

    Returns:
    str: A 6-character Maidenhead locator.
    """

    grid_square = grid_square.upper()

    # If the grid square is longer than 6 characters, strip it to 6 characters
    if len(grid_square) > 6:
        grid_square = grid_square[:6]

    if len(grid_square) == 2:
        # Generate random digits for positions 3 and 4
        grid_square += f"{random.randint(0, 9)}{random.randint(0, 9)}"
        # Generate random lowercase letters from 'a' to 'r' for positions 5 and 6
        grid_square += random.choice("abcdefghijklmnopqr")
        grid_square += random.choice("abcdefghijklmnopqr")

    elif len(grid_square) == 4:
        # Generate random lowercase letters from 'a' to 'r' for positions 5 and 6
        grid_square += random.choice("abcdefghijklmnopqr")
        grid_square += random.choice("abcdefghijklmnopqr")

    elif len(grid_square) == 6:
        # If grid square is valid and already 6 characters, enforce format
        grid_square = grid_square[:2].upper() + grid_square[2:4] + grid_square[4:6].lower()
        return grid_square

    else:
        raise ValueError("Grid square must be 2, 4, or 6 characters long.")

    # Adjust the case for the last two characters
    grid_square = grid_square[:4] + grid_square[4:].lower()
    return grid_square