Better poi index computation

src/closest.ts

@@ -0,0 +1,171 @@
+/**
+ * @module ol/geom/flat/closest
+ */
+import {lerp, squaredDistance as squaredDx} from 'ol/math.js';
+
+/*
+ * Returns the point on the 2D line segment flatCoordinates[offset1] to
+ * flatCoordinates[offset2] that is closest to the point (x, y).  Extra
+ * dimensions are linearly interpolated.
+ */
+function assignClosest(
+  flatCoordinates: number[],
+  offset1: number,
+  offset2: number,
+  stride: number,
+  x: number,
+  y: number,
+  closestPoint: number[]
+) {
+  const x1 = flatCoordinates[offset1];
+  const y1 = flatCoordinates[offset1 + 1];
+  const dx = flatCoordinates[offset2] - x1;
+  const dy = flatCoordinates[offset2 + 1] - y1;
+  let offset;
+  if (dx === 0 && dy === 0) {
+    offset = offset1;
+  } else {
+    const t = ((x - x1) * dx + (y - y1) * dy) / (dx * dx + dy * dy);
+    if (t > 1) {
+      offset = offset2;
+    } else if (t > 0) {
+      for (let i = 0; i < stride; ++i) {
+        closestPoint[i] = lerp(
+          flatCoordinates[offset1 + i],
+          flatCoordinates[offset2 + i],
+          t
+        );
+      }
+      closestPoint.length = stride;
+      return;
+    } else {
+      offset = offset1;
+    }
+  }
+  for (let i = 0; i < stride; ++i) {
+    closestPoint[i] = flatCoordinates[offset + i];
+  }
+  closestPoint.length = stride;
+}
+
+type ClosestPointResult = {
+  totalSquaredDistance: number;
+  squaredDistance: number;
+  closestPoint: number[];
+}
+
+export function getClosestPoint(
+  flatCoordinates: number[],
+  offset: number,
+  end: number,
+  stride: number,
+  maxDelta: number,
+  x: number,
+  y: number
+): ClosestPointResult {
+  let minSquaredDistance = Infinity;
+  const closestPoint = [NaN, NaN];
+  let minIndex;
+  if (offset == end) {
+    return {
+      closestPoint: closestPoint,
+      squaredDistance: minSquaredDistance,
+      totalSquaredDistance: minSquaredDistance,
+    };
+  }
+  let i, squaredDistance;
+  if (maxDelta === 0) {
+    // All points are identical, so just test the first point.
+    squaredDistance = squaredDx(
+      x,
+      y,
+      flatCoordinates[offset],
+      flatCoordinates[offset + 1]
+    );
+    if (squaredDistance < minSquaredDistance) {
+      for (i = 0; i < stride; ++i) {
+        closestPoint[i] = flatCoordinates[offset + i];
+      }
+      closestPoint.length = stride;
+      return {
+        closestPoint: closestPoint,
+        squaredDistance: squaredDistance,
+        totalSquaredDistance: squaredDx(
+          flatCoordinates[offset],
+          flatCoordinates[offset + 1],
+          closestPoint[0],
+          closestPoint[1]
+        ),
+      };
+    }
+    return {
+      closestPoint: closestPoint,
+      squaredDistance: minSquaredDistance,
+      totalSquaredDistance: minSquaredDistance,
+    };
+  }
+  const tmpPoint = [NaN, NaN];
+  let index = offset + stride;
+  while (index < end) {
+    assignClosest(
+      flatCoordinates,
+      index - stride,
+      index,
+      stride,
+      x,
+      y,
+      tmpPoint
+    );
+    squaredDistance = squaredDx(x, y, tmpPoint[0], tmpPoint[1]);
+    if (squaredDistance < minSquaredDistance) {
+      minSquaredDistance = squaredDistance;
+      minIndex = index;
+      for (i = 0; i < stride; ++i) {
+        closestPoint[i] = tmpPoint[i];
+      }
+      closestPoint.length = stride;
+      index += stride;
+    } else {
+      // console.log('no match', index);
+      // Skip ahead multiple points, because we know that all the skipped
+      // points cannot be any closer than the closest point we have found so
+      // far.  We know this because we know how close the current point is, how
+      // close the closest point we have found so far is, and the maximum
+      // distance between consecutive points.  For example, if we're currently
+      // at distance 10, the best we've found so far is 3, and that the maximum
+      // distance between consecutive points is 2, then we'll need to skip at
+      // least (10 - 3) / 2 == 3 (rounded down) points to have any chance of
+      // finding a closer point.  We use Math.max(..., 1) to ensure that we
+      // always advance at least one point, to avoid an infinite loop.
+      index +=
+        stride *
+        Math.max(
+          ((Math.sqrt(squaredDistance) - Math.sqrt(minSquaredDistance)) /
+            maxDelta) |
+            0,
+          1
+        );
+    }
+  }
+  let totalSquaredDistance = 0;
+  for (i = offset + stride; i < minIndex; ++i) {
+    totalSquaredDistance += squaredDx(
+      flatCoordinates[i - stride],
+      flatCoordinates[i - stride + 1],
+      flatCoordinates[i],
+      flatCoordinates[i + 1]
+    )
+  }
+  totalSquaredDistance += squaredDx(
+    flatCoordinates[minIndex],
+    flatCoordinates[minIndex + 1],
+    closestPoint[0],
+    closestPoint[1]
+  );
+
+  return {
+    totalSquaredDistance: totalSquaredDistance,
+    squaredDistance: minSquaredDistance,
+    closestPoint: closestPoint,
+  }
+}

src/interaction/TrackData.ts

@@ -1,10 +1,12 @@
 import {equals} from 'ol/coordinate.js';
 import Feature from 'ol/Feature.js';
 import LineString from 'ol/geom/LineString.js';
-import MultiPoint from 'ol/geom/MultiPoint.js';
+import {maxSquaredDelta} from 'ol/geom/flat/closest.js';
+import {getClosestPoint} from '../closest.ts';
 import type Point from 'ol/geom/Point.js';
 import type {Coordinate} from 'ol/coordinate.js';
 
+
 interface ParsedFeatures {
   segments: Array<Feature<LineString>>;
   controlPoints: Array<Feature<Point>>;
@@ -257,17 +259,18 @@ export default class TrackData {
   }
 
   updatePOIIndexes() {
-    // build a multi point geometry from all segments coordinates
-    const points = new MultiPoint(this.segments.map((s) => s.getGeometry().getCoordinates()).flat());
-    const pointsCoordinates = points.getCoordinates();
+    const lineFlatCoordinates = this.segments.map(s => s.getGeometry().getFlatCoordinates()).flat()
+    const lineMaxDelta = maxSquaredDelta(lineFlatCoordinates, 0, lineFlatCoordinates.length, 2, 0)
+
     const sorted = this.pois.map((poi) => {
-      // find the closest point to the POI and returns its index; that's it's "distance" from the start
-      const closestPoint = points.getClosestPoint(poi.getGeometry().getCoordinates());
+      const point = poi.getGeometry().getCoordinates();
+      const {totalSquaredDistance} = getClosestPoint(lineFlatCoordinates, 0, lineFlatCoordinates.length, 2, lineMaxDelta, point[0], point[1]);
+
       return {
         poi: poi,
-        index: pointsCoordinates.findIndex((c) => equals(c, closestPoint))
+        distance: totalSquaredDistance
       };
-    }).sort((a, b) => a.index - b.index);
+    }).sort((a, b) => a.distance - b.distance);
     sorted.forEach((s, index) => s.poi.set('index', index));
   }