grid-index

grid-index

GridIndex is a 2D spatial index that is transferable.

Pairs of keys and boxes can be inserted into GridIndex. The grid can then be queried to find all the keys that intersect a given box. The grid can be serialized to an ArrayBuffer so that it can be transferred between WebWorkers.

You should probably use rbush instead of GridIndex! It's easier to use and it's as fast or faster in many cases.

GridIndex can be faster in a specific set of cases:

• the constructed index needs to be transferred between workers
• the extent of the features is fixed
• features are somewhat evenly sized and distributed
• a high number of insertions relative to the number of queries

GridIndex is used by mapbox-gl-js for label collision detection and feature picking.

Example

var GridIndex = require('grid-index');

var grid = new GridIndex(100, 5, 0);
var key1 = 1;
var key2 = 2;
var key3 = 3;
grid.insert(key1, 30, 10, 35, 15);
grid.insert(key2, 60, 20, 65, 25);
grid.insert(key3, 40, 10, 45, 15);

var keys = grid.query(0, 0, 100, 13);
// `keys` is now [key1, key3]

var arrayBuffer = grid.toArrayBuffer();
// transfer the ArrayBuffer to a different worker 

var grid2 = new GridIndex(arrayBuffer);
var keys2 = grid2.query(0, 0, 100, 13);
// `keys2` is now [key1, key3]

API

GridIndex(extent, n, padding)

Create a new GridIndex.

• extent: The width and height of the square area that needs to be indexed, for example 4096.
• n: The rows and columns the grid will be split into. 4 would divide the grid into 16 cells.
• padding: The number of extra rows and columns that should be added on each side of the main grid square.

GridIndex(arrayBuffer)

Unserialize a GridIndex.

• arrayBuffer: an ArrayBuffer produced by gridIndex.toArrayBuffer().

gridIndex.insert(key, x1, x2, y1, y2)

Insert a new key, box pair into the grid.

• key: An unsigned 32bit integer.
• x1: The x coordinate of the left edge of the box.
• x2: The x coordinate of the right edge of the box.
• y1: The y coordinate of the top edge of the box.
• y2: The y coordinate of the bottom edge of the box.

gridIndex.query(key, x1, x2, y1, y2)

Find the keys that intersect with the given box.

• x1: The x coordinate of the left edge of the box.
• x2: The x coordinate of the right edge of the box.
• y1: The y coordinate of the top edge of the box.
• y2: The y coordinate of the bottom edge of the box.

returns an array of keys.

gridIndex.toArrayBuffer()

Serialize a GridIndex to an ArrayBuffer so that it can be transferred between WebWorkers efficiently.

returns an ArrayBuffer that can later be deserialized with new GridIndex(arrayBuffer).