StackGenVis: Alignment of Data, Algorithms, and Models for Stacking Ensemble Learning Using Performance Metrics
https://doi.org/10.1109/TVCG.2020.3030352
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86 lines
3.1 KiB
86 lines
3.1 KiB
4 years ago
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# grid-index
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GridIndex is a 2D spatial index that is [transferable](https://developer.mozilla.org/en-US/docs/Web/API/Transferable).
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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.
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**You should probably use [rbush](https://github.com/mourner/rbush) instead of GridIndex!** It's easier to use and it's as fast or faster in many cases.
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GridIndex can be faster in a specific set of cases:
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- the constructed index needs to be transferred between workers
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- the extent of the features is fixed
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- features are somewhat evenly sized and distributed
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- a high number of insertions relative to the number of queries
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GridIndex is used by [mapbox-gl-js](https://github.com/mapbox/mapbox-gl-js) for label collision detection and feature picking.
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## Example
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```js
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var GridIndex = require('grid-index');
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var grid = new GridIndex(100, 5, 0);
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var key1 = 1;
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var key2 = 2;
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var key3 = 3;
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grid.insert(key1, 30, 10, 35, 15);
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grid.insert(key2, 60, 20, 65, 25);
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grid.insert(key3, 40, 10, 45, 15);
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var keys = grid.query(0, 0, 100, 13);
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// `keys` is now [key1, key3]
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var arrayBuffer = grid.toArrayBuffer();
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// transfer the ArrayBuffer to a different worker
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var grid2 = new GridIndex(arrayBuffer);
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var keys2 = grid2.query(0, 0, 100, 13);
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// `keys2` is now [key1, key3]
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```
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## API
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### `GridIndex(extent, n, padding)`
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Create a new GridIndex.
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- **extent**: The width and height of the square area that needs to be indexed, for example `4096`.
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- **n**: The rows and columns the grid will be split into. `4` would divide the grid into 16 cells.
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- **padding**: The number of extra rows and columns that should be added on each side of the main grid square.
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### `GridIndex(arrayBuffer)`
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Unserialize a GridIndex.
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- **arrayBuffer**: an ArrayBuffer produced by `gridIndex.toArrayBuffer()`.
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### `gridIndex.insert(key, x1, y1, x2, y2)`
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Insert a new key, box pair into the grid.
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- **key**: An unsigned 32bit integer.
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- **x1**: The x coordinate of the left edge of the box.
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- **y1**: The y coordinate of the bottom edge of the box.
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- **x2**: The x coordinate of the right edge of the box.
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- **y2**: The y coordinate of the top edge of the box.
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### `gridIndex.query(key, x1, y1, x2, y2, intersectionTest?)`
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Find the keys that intersect with the given box.
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- **x1**: The x coordinate of the left edge of the box.
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- **y1**: The y coordinate of the bottom edge of the box.
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- **x2**: The x coordinate of the right edge of the box.
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- **y2**: The y coordinate of the top edge of the box.
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- **intersectionTest**: An optional function that can be used to filter results by bbox. If provided, this function is called for each possible result with four arguments: x1, y1, x2, y2. Return true to include the result in the returned value.
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**returns** an array of keys.
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### `gridIndex.toArrayBuffer()`
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Serialize a GridIndex to an ArrayBuffer so that it can be transferred between WebWorkers efficiently.
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**returns** an ArrayBuffer that can later be deserialized with `new GridIndex(arrayBuffer)`.
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