50 lines
1.3 KiB
TypeScript
50 lines
1.3 KiB
TypeScript
/**
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* Decodes an encoded Polyline string into an array of [lng, lat] coordinates.
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* @param str The encoded polyline string
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* @param precision The precision of the coordinates (default 5 for Google Polyline)
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* @returns Array of [lng, lat] coordinates
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*/
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export function decodePolyline(str: string, precision: number = 5): [number, number][] {
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let index = 0;
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let lat = 0;
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let lng = 0;
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const coordinates: [number, number][] = [];
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let shift = 0;
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let result = 0;
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let byte: number | null = null;
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let latitude_change: number;
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let longitude_change: number;
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const factor = Math.pow(10, precision);
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while (index < str.length) {
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byte = null;
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shift = 0;
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result = 0;
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do {
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byte = str.charCodeAt(index++) - 63;
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result |= (byte & 0x1f) << shift;
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shift += 5;
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} while (byte >= 0x20);
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latitude_change = ((result & 1) ? ~(result >> 1) : (result >> 1));
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lat += latitude_change;
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shift = 0;
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result = 0;
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do {
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byte = str.charCodeAt(index++) - 63;
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result |= (byte & 0x1f) << shift;
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shift += 5;
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} while (byte >= 0x20);
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longitude_change = ((result & 1) ? ~(result >> 1) : (result >> 1));
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lng += longitude_change;
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coordinates.push([lng / factor, lat / factor]);
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}
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return coordinates;
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}
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