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feat(contourSeg): polyline performance improvements (#1061)
* feat(contourSeg): polyline simplication (Ramer–Douglas–Peucker) * feat(contourSeg): polyline simplification (improvements) * update api * code review * update api * feat(contourSeg) polyline decimate :: code review
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,105 @@ | ||
| import type { Types } from '@cornerstonejs/core'; | ||
| import * as mathLine from '../line'; | ||
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| const DEFAULT_EPSILON = 0.1; | ||
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| /** | ||
| * Ramer–Douglas–Peucker algorithm implementation to decimate a polyline | ||
| * to a similar polyline with fewer points | ||
| * | ||
| * https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm | ||
| * https://rosettacode.org/wiki/Ramer-Douglas-Peucker_line_simplification | ||
| * https://karthaus.nl/rdp/ | ||
| * | ||
| * @param polyline - Polyline to decimate | ||
| * @param epsilon - A maximum given distance 'epsilon' to decide if a point | ||
| * should or shouldn't be added the decimated polyline version. In each | ||
| * iteration the polyline is split into two polylines and the distance of each | ||
| * point from those new polylines are checked against the line that connects | ||
| * the first and last points. | ||
| * @returns Decimated polyline | ||
| */ | ||
| export default function decimate( | ||
| polyline: Types.Point2[], | ||
| epsilon = DEFAULT_EPSILON | ||
| ) { | ||
| const numPoints = polyline.length; | ||
|
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| // The polyline must have at least a start and end points | ||
| if (numPoints < 3) { | ||
| return polyline; | ||
| } | ||
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| const epsilonSquared = epsilon * epsilon; | ||
| const partitionQueue = [[0, numPoints - 1]]; | ||
|
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| // Used a boolean array to set each point that will be in the decimated polyline | ||
| // because pre-allocated arrays are 3-4x faster than thousands of push() calls | ||
| // to add all points to a new array. | ||
| const polylinePointFlags = new Array(numPoints).fill(false); | ||
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| // Start and end points are always added to the decimated polyline | ||
| let numDecimatedPoints = 2; | ||
|
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| // Add start and end points to the decimated polyline | ||
| polylinePointFlags[0] = true; | ||
| polylinePointFlags[numPoints - 1] = true; | ||
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| // Iterative approach using a queue instead of recursion to reduce the number | ||
| // of function calls (performance) | ||
| while (partitionQueue.length) { | ||
| const [startIndex, endIndex] = partitionQueue.pop(); | ||
|
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| // Return if there is no point between the start and end points | ||
| if (endIndex - startIndex === 1) { | ||
| continue; | ||
| } | ||
|
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| const startPoint = polyline[startIndex]; | ||
| const endPoint = polyline[endIndex]; | ||
| let maxDistSquared = -Infinity; | ||
| let maxDistIndex = -1; | ||
|
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| // Search for the furthest point | ||
| for (let i = startIndex + 1; i < endIndex; i++) { | ||
| const currentPoint = polyline[i]; | ||
| const distSquared = mathLine.distanceToPointSquared( | ||
| startPoint, | ||
| endPoint, | ||
| currentPoint | ||
| ); | ||
|
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| if (distSquared > maxDistSquared) { | ||
| maxDistSquared = distSquared; | ||
| maxDistIndex = i; | ||
| } | ||
| } | ||
|
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| // Do not add any of the points because the fursthest one is very close to | ||
| // the line based on the epsilon value | ||
| if (maxDistSquared < epsilonSquared) { | ||
| continue; | ||
| } | ||
|
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| // Update the flag for the furthest point because it will be added to the | ||
| // decimated polyline | ||
| polylinePointFlags[maxDistIndex] = true; | ||
| numDecimatedPoints++; | ||
|
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| // Partition the points into two parts using maxDistIndex as the pivot point | ||
| // and process both sides | ||
| partitionQueue.push([maxDistIndex, endIndex]); | ||
| partitionQueue.push([startIndex, maxDistIndex]); | ||
| } | ||
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| // A pre-allocated array is 3-4x faster then multiple push() calls | ||
| const decimatedPolyline: Types.Point2[] = new Array(numDecimatedPoints); | ||
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| for (let srcIndex = 0, dstIndex = 0; srcIndex < numPoints; srcIndex++) { | ||
| if (polylinePointFlags[srcIndex]) { | ||
| decimatedPolyline[dstIndex++] = polyline[srcIndex]; | ||
| } | ||
| } | ||
|
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| return decimatedPolyline; | ||
| } |
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