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feat(geo): Add an optional bias when rounding bounds #1033

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Aug 10, 2020
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feat(geo): Add an optional bias when rounding bounds #1033

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3 changes: 3 additions & 0 deletions packages/geo/src/__tests__/bounds.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,9 @@ o.spec('Bounds', () => {
o(new Bounds(1.1, 10.1, 12.2, 11.2).round().toJson()).deepEquals({ x: 1, y: 10, width: 12, height: 11 });
o(new Bounds(1.4, 10.6, 12.2, 11.4).round().toJson()).deepEquals({ x: 1, y: 11, width: 13, height: 11 });
o(new Bounds(0.4, 0.6, 2.4, 1.6).round().toJson()).deepEquals({ x: 0, y: 1, width: 3, height: 1 });

o(new Bounds(1.6, 10.6, 12.5, 11.5).round().toJson()).deepEquals({ x: 2, y: 11, width: 12, height: 11 });
o(new Bounds(1.6, 10.6, 12.5, 11.5).round(0.2).toJson()).deepEquals({ x: 1, y: 10, width: 13, height: 12 });
});

o('toBbox', () => {
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11 changes: 7 additions & 4 deletions packages/geo/src/bounds.ts
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Expand Up @@ -158,11 +158,14 @@ export class Bounds implements BoundingBox {

/**
* Round dimensions to integers keeping the error a low as possible

* @param bias influence the rounding in favour of a larger area (+ve bias) or smaller area (-ve
* bias). Example: bias = 0.2 would round left and top down when < 0.7 and round right and bottom up when >= 0.3
*/
public round(): Bounds {
const x = Math.round(this.x);
const y = Math.round(this.y);
return new Bounds(x, y, Math.round(this.right) - x, Math.round(this.bottom) - y);
public round(bias = 0): Bounds {
const x = Math.round(this.x - bias);
const y = Math.round(this.y - bias);
return new Bounds(x, y, Math.round(this.right + bias) - x, Math.round(this.bottom + bias) - y);
}

public add(bounds: Point): Bounds {
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5 changes: 4 additions & 1 deletion packages/tiler/src/tiler.ts
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Expand Up @@ -13,6 +13,9 @@ export interface RasterPixelBounds {
tiff: Bounds;
}

/** The amount to bias the Bounds.round function to cover a larger, rather than smaller, area. */
const ROUND_BIAS = 0.2;

export class Tiler {
/** Tile size for the tiler and sub objects */
public readonly tms: TileMatrixSet;
Expand Down Expand Up @@ -78,7 +81,7 @@ export class Tiler {
): Composition | null {
const source = Bounds.fromJson(img.getTileBounds(x, y));

const target = source.scale(scaleFactor, scaleFactor).add(raster.tiff).round();
const target = source.scale(scaleFactor, scaleFactor).add(raster.tiff).round(ROUND_BIAS);

// Validate that the requested COG tile actually intersects with the output raster
const tileIntersection = target.intersection(raster.tile);
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