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Edited
Apr 10, 2023
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H3
lookupMap = bartStations.features.reduce((map, feature) => {
// Make a map like {[hexagon]: [id, id, ...]}
const [lon, lat] = feature.geometry.coordinates;
const h3Index = h3.latLngToCell(lat, lon, res);
if (!map[h3Index]) map[h3Index] = [];
map[h3Index].push(feature);
return map;
}, {})
function kRingResults(searchLocation) {
const lookupIndexes = kRingIndexes(searchLocation);
// Find all points of interest in the k-ring
return lookupIndexes.reduce((output, h3Index) => [...output, ...(lookupMap[h3Index] || [])], []);
}
kRingIndexes = radiusMethod === 'edge' ? kRingIndexesEdge : kRingIndexesArea
/**
* Calculate the indexes within the radius based on average cell edge length
*/
function kRingIndexesEdge(searchLocation, pad = 0) {
const origin = h3.latLngToCell(searchLocation.lat, searchLocation.lng, res);
// Transform the radius from km to grid distance
const radius = Math.floor(searchRadiusKm / (h3.getHexagonEdgeLengthAvg(res, h3.UNITS.km) * 2)) + pad;
return h3.gridDisk(origin, radius);
}
/**
* Calculate the indexes within the radius based on the search area
*/
function kRingIndexesArea(searchLocation) {
const origin = h3.latLngToCell(searchLocation.lat, searchLocation.lng, res);
const originArea = h3.cellArea(origin, h3.UNITS.km2);
const searchArea = Math.PI * searchRadiusKm * searchRadiusKm;
let radius = 0;
let diskArea = originArea;
while (diskArea < searchArea) {
radius++;
const cellCount = 3 * radius * (radius + 1) + 1;
diskArea = cellCount * originArea;
}
return h3.gridDisk(origin, radius);
}
function haversineResults(searchLocation) {
return bartStations.features.filter(
feature => haversineDistance(
[searchLocation.lng, searchLocation.lat],
feature.geometry.coordinates,
{units: 'kilometers'}
) < searchRadiusKm
);
}
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