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import { utilities } from '@cornerstonejs/core';
import type { PointsArray3 } from './interpolate';
const { PointsManager } = utilities;
/**
* Selects handles by looking for local maximums in the angle that the local
* vector makes
*
* @param polyline - an array of points, usually the polyline for the contour to
* select handles from.
* @param handleCount - a guideline for how many handles to create
*/
export default function selectHandles(
polyline: PointsArray3,
handleCount = 12
): PointsArray3 {
const handles = PointsManager.create3(handleCount) as PointsArray3;
handles.sources = [];
const { sources: destPoints } = handles;
const { length, sources: sourcePoints = [] } = polyline;
// The distance used for figuring out the local angle of a line
const distance = 5;
if (length < distance * 3) {
return polyline.subselect(handleCount);
}
// Need to make the interval between handles long enough to allow for some
// variation between points in terms of the distance of a line angle, but
// also not too many handles either.
// On average, we get twice the interval between handles, so double the length here.
// Or, choose a longer interval if the handle count would have too many handles (too short an interval)
const interval = Math.floor(
Math.max((2 * length) / handleCount, distance * 2)
);
sourcePoints.forEach(() =>
destPoints.push(PointsManager.create3(handleCount))
);
const dotValues = createDotValues(polyline, distance);
const minimumRegions = findMinimumRegions(dotValues, handleCount);
const indices = [];
if (minimumRegions?.length > 2) {
let lastHandle = -1;
const thirdInterval = interval / 3;
minimumRegions.forEach((region) => {
const [start, , end] = region;
const midIndex = Math.ceil((start + end) / 2);
if (end - lastHandle < thirdInterval) {
return;
}
Iif (midIndex - start > 2 * thirdInterval) {
addInterval(indices, lastHandle, start, interval, length);
lastHandle = addInterval(indices, start, midIndex, interval, length);
} else {
lastHandle = addInterval(
indices,
lastHandle,
midIndex,
interval,
length
);
}
Iif (end - lastHandle > thirdInterval) {
lastHandle = addInterval(indices, lastHandle, end, interval, length);
}
});
const firstHandle = indices[0];
const lastDistance = indexValue(firstHandle + length - lastHandle, length);
// Check that there is enough space between the last and first handle to
// need an extra handle.
Eif (lastDistance > 2 * thirdInterval) {
addInterval(
indices,
lastHandle,
// Don't add a point too close to the first handle
firstHandle - thirdInterval,
interval,
length
);
}
} else E{
const interval = Math.floor(length / handleCount);
addInterval(indices, -1, length - interval, interval, length);
}
indices.forEach((index) => {
const point = polyline.getPointArray(index);
handles.push(point);
sourcePoints.forEach((source, destSourceIndex) =>
destPoints[destSourceIndex].push(source.getPoint(index))
);
});
return handles;
}
/**
* Creates an array of the dot products between each point in the points array
* and a point +/- distance from that point, unitized to vector length 1.
* That is, this is a measure of the angle at the given point, where 1 is a
* straight line, and -1 is a 180 degree angle change.
*
* @param polyline - the array of Point3 values
* @param distance - previous/next distance to use for the vectors for the dot product
* @returns - Float32Array of dot products, one per point in the source array.
*/
export function createDotValues(
polyline: PointsArray3,
distance = 6
): Float32Array {
const { length } = polyline;
const prevVec3 = vec3.create();
const nextVec3 = vec3.create();
const dotValues = new Float32Array(length);
for (let i = 0; i < length; i++) {
const point = polyline.getPoint(i);
const prevPoint = polyline.getPoint(i - distance);
const nextPoint = polyline.getPoint((i + distance) % length);
vec3.sub(prevVec3, point, prevPoint);
vec3.sub(nextVec3, nextPoint, point);
const dot =
vec3.dot(prevVec3, nextVec3) / (vec3.len(prevVec3) * vec3.len(nextVec3));
dotValues[i] = dot;
}
return dotValues;
}
/**
* Finds minimum regions in the dot products. These are detected as
* center points of the dot values regions having a minimum value - that is,
* where the direction of the line is changing fastest.
*/
function findMinimumRegions(dotValues, handleCount) {
const { max, deviation } = getStats(dotValues);
const { length } = dotValues;
// Fallback for very uniform ojects.
Iif (deviation < 0.01 || length < handleCount * 3) {
return [];
}
const inflection = [];
let pair = null;
let minValue;
let minIndex = 0;
for (let i = 0; i < length; i++) {
const dot = dotValues[i];
if (dot < max - deviation) {
if (pair) {
pair[2] = i;
if (dot < minValue) {
minValue = dot;
minIndex = i;
}
pair[1] = minIndex;
} else {
minValue = dot;
minIndex = i;
pair = [i, i, i];
}
} else {
if (pair) {
inflection.push(pair);
pair = null;
}
}
}
Eif (pair) {
if (inflection[0][0] === 0) {
inflection[0][0] = pair[0];
} else E{
pair[1] = minIndex;
pair[2] = length - 1;
inflection.push(pair);
}
}
return inflection;
}
/**
* Adds points in between the start and finish.
* This is currently just the center point for short values and the start/center/end
* for ranges where the distance between these is at least the increment.
*/
export function addInterval(indices, start, finish, interval, length) {
if (finish < start) {
// Always want a positive distance even if the long way round
finish += length;
}
const distance = finish - start;
const count = Math.ceil(distance / interval);
Iif (count <= 0) {
if (indices[indices.length - 1] !== finish) {
indices.push(indexValue(finish, length));
}
return finish;
}
// Don't add the start index, and always add the end index
for (let i = 1; i <= count; i++) {
const index = indexValue(start + (i * distance) / count, length);
indices.push(index);
}
return indices[indices.length - 1];
}
/**
* Gets the index value of a closed polyline, rounding the value and
* doing the module operation as required.
*/
function indexValue(v, length) {
return (Math.round(v) + length) % length;
}
/**
* Gets statistics on the provided array numbers.
*/
function getStats(dotValues) {
const { length } = dotValues;
let sum = 0;
let min = Infinity;
let max = -Infinity;
let sumSq = 0;
for (let i = 0; i < length; i++) {
const dot = dotValues[i];
sum += dot;
min = Math.min(min, dot);
max = Math.max(max, dot);
}
const mean = sum / length;
for (let i = 0; i < length; i++) {
const valueDiff = dotValues[i] - mean;
sumSq += valueDiff * valueDiff;
}
return {
mean,
max,
min,
sumSq,
deviation: Math.sqrt(sumSq / length),
};
}
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