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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | 2x 2x 2x 2x 1280x 1280x 1280x 1280x 1280x 1280x 1280x 1280x 2x 2x | import type { Types } from '@cornerstonejs/core';
/**
* Returns the area with signal of a 2D polyline
* https://www.youtube.com/watch?v=GpsKrAipXm8&t=1900s
*
* This functions has a runtime very close to `getArea` and it is recommended to
* be called only if you need the area signal (eg: calculate polygon normal or
* winding direction). If you do not need the area signal you should always call
* `getArea`.
*
* @param polyline - Polyline points (2D)
* @returns Area of the polyline (with signal)
*/
export default function getSignedArea(polyline: Types.Point2[]): number {
Iif (polyline.length < 3) {
return 0;
}
// Reference point can be any point on the same plane
const refPoint = polyline[0];
let area = 0;
// Takes three points (reference point and two other points from each line
// segment) and calculate the area with cross product. The magnitude of the
// vector returned by a cross product is equal to the area of the parallelogram
// that the vectors span which is two times the area of the triangle.
//
// Not calling vec3 mathods makes the function run much faster since polylines
// may have thousands of points when using freehand ROI tool and that would
// increase considerably the number of function calls.
for (let i = 0, len = polyline.length; i < len; i++) {
const p1 = polyline[i];
// Using ternary instead of % (mod) operator to make it faster
const p2Index = i === len - 1 ? 0 : i + 1;
const p2 = polyline[p2Index];
const aX = p1[0] - refPoint[0];
const aY = p1[1] - refPoint[1];
const bX = p2[0] - refPoint[0];
const bY = p2[1] - refPoint[1];
// Cross product between vectors "a" and "b" which returns (0, 0, crossProd)
// for 2D vectors.
area += aX * bY - aY * bX;
}
// Divide by two because cross product returns two times the area for each triangle
area *= 0.5;
return area;
}
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