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Indexing

Functions for converting between geospatial coordinates and A5 indices.

Coordinates are specified as per the GeoJSON spec, namely: [longitude, latitude].

lonLatToCell​

Indexes the coordinate at a given resolution to an A5 cell index.

function lonLatToCell(coordinate: [longitude: number, latitude: number], resolution: number): bigint;

Parameters​

  • coordinate (number[]) coordinate as [longitude, latitude]
  • resolution (number) The resolution level to index at

Return value​

  • (bigint) The A5 cell identifier

cellToLonLat​

Returns the geospatial coordinate at the center of an A5 cell.

function cellToLonLat(cell: bigint): [longitude: number, latitude: number];

Parameters​

  • cell (bigint) A5 cell identifier

Return value​

  • (number[]) The center coordinate as [longitude, latitude]

cellToBoundary​

Returns the five vertices that define the boundary of an A5 cell.

function cellToBoundary(cell: bigint): [longitude: number, latitude: number][];

Parameters​

  • cell (bigint) A5 cell identifier

Return value​

  • (number[][]) Array of five coordinates, each as [longitude, latitude]

Cell representation​

A5 cells are stored as 64 bit integers, for performance and to provide a compact representation for use in databases. In JavaScript these can be represented as BigInt values and collections stored as BigInt64Arrays.

For best performance it is recommened to use this representation, but it is also possible to convert them into hexidecimal, for example to encode them in JSON (which does not support 64 bit integers). Two helper functions are provided for this conversion.

bigIntToHex​

function bigIntToHex(index: bigint): string;

Parameters​

  • index (bigint) A5 cell identifier

Return value​

  • (string) Hexadecimal string representation of the cell identifier

hexToBigInt​

function hexToBigInt(hex: string): bigint;

Parameters​

  • hex (string) Hexadecimal string representation of an A5 cell identifier

Return value​

  • (bigint) The A5 cell identifier