web_lib

Common web application libraries
git clone https://radroots.dev/git/web_lib.git
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bounds.ts (3045B)

      1 import type { GeolocationPoint } from "./types.js";
      2 
      3 const EARTH_RADIUS = 6371;
      4 
      5 export const compute_bounding_box = (
      6     lat: number,
      7     lng: number,
      8     distance_km: number
      9 ): {
     10     nw: GeolocationPoint;
     11     ne: GeolocationPoint;
     12     se: GeolocationPoint;
     13     sw: GeolocationPoint;
     14 } => {
     15     const deg_to_rad = (deg: number) => deg * (Math.PI / 180);
     16     const rad_to_deg = (rad: number) => rad * (180 / Math.PI);
     17 
     18     function destination_point(
     19         lat: number,
     20         lng: number,
     21         bearing: number,
     22         distance_km: number
     23     ): GeolocationPoint {
     24         const lat1 = deg_to_rad(lat);
     25         const lon1 = deg_to_rad(lng);
     26         const angular_distance = distance_km / EARTH_RADIUS;
     27 
     28         const lat2 = Math.asin(
     29             Math.sin(lat1) * Math.cos(angular_distance)
     30                 + Math.cos(lat1)
     31                 * Math.sin(angular_distance)
     32                 * Math.cos(deg_to_rad(bearing))
     33         );
     34         const lon2 = lon1
     35             + Math.atan2(
     36                 Math.sin(deg_to_rad(bearing))
     37                     * Math.sin(angular_distance)
     38                     * Math.cos(lat1),
     39                 Math.cos(angular_distance) - Math.sin(lat1) * Math.sin(lat2)
     40             );
     41 
     42         return { lat: rad_to_deg(lat2), lng: rad_to_deg(lon2) };
     43     }
     44 
     45     const bearings = [0, 90, 180, 270];
     46 
     47     const coords = bearings.map((bearing) =>
     48         destination_point(lat, lng, bearing, distance_km / Math.sqrt(2))
     49     );
     50 
     51     return {
     52         nw: coords[0],
     53         ne: coords[1],
     54         se: coords[2],
     55         sw: coords[3],
     56     };
     57 };
     58 
     59 export const geo_bounds_calc = (
     60     lat: number,
     61     lng: number,
     62     distance_km: number
     63 ): {
     64     north: GeolocationPoint;
     65     south: GeolocationPoint;
     66     east: GeolocationPoint;
     67     west: GeolocationPoint;
     68 } => {
     69     const deg_to_rad = (deg: number) => deg * (Math.PI / 180);
     70     const rad_to_deg = (rad: number) => rad * (180 / Math.PI);
     71 
     72     function destination_point(
     73         lat: number,
     74         lng: number,
     75         bearing: number,
     76         distance_km: number
     77     ): GeolocationPoint {
     78         const lat1 = deg_to_rad(lat);
     79         const lon1 = deg_to_rad(lng);
     80         const angular_distance = distance_km / EARTH_RADIUS;
     81 
     82         const lat2 = Math.asin(
     83             Math.sin(lat1) * Math.cos(angular_distance)
     84                 + Math.cos(lat1)
     85                 * Math.sin(angular_distance)
     86                 * Math.cos(deg_to_rad(bearing))
     87         );
     88         const lon2 = lon1
     89             + Math.atan2(
     90                 Math.sin(deg_to_rad(bearing))
     91                     * Math.sin(angular_distance)
     92                     * Math.cos(lat1),
     93                 Math.cos(angular_distance) - Math.sin(lat1) * Math.sin(lat2)
     94             );
     95 
     96         return { lat: rad_to_deg(lat2), lng: rad_to_deg(lon2) };
     97     }
     98 
     99     return {
    100         north: destination_point(lat, lng, 0, distance_km),
    101         south: destination_point(lat, lng, 180, distance_km),
    102         east: destination_point(lat, lng, 90, distance_km),
    103         west: destination_point(lat, lng, 270, distance_km),
    104     };
    105 };