Implemented spirals close approach

common/api/core-geometry.api.md

@@ -1711,7 +1711,7 @@ export class CurveLocationDetail {
     isSameCurveAndFraction(other: CurveLocationDetail | {
         curve: CurvePrimitive;
         fraction: number;
-    }): boolean;
+    }, fractionTol?: number): boolean;
     point: Point3d;
     point1?: Point3d;
     pointQ: Point3d;
@@ -2224,6 +2224,7 @@ export class Geometry {
     static isSameCoordinateSquared(x: number, y: number, tolerance?: number): boolean;
     static isSameCoordinateWithToleranceFactor(x: number, y: number, toleranceFactor: number): boolean;
     static isSameCoordinateXY(x0: number, y0: number, x1: number, y1: number, tolerance?: number): boolean;
+    static isSameFraction(x: number, y: number, tolerance?: number): boolean;
     static isSamePoint2d(dataA: Point2d, dataB: Point2d, tolerance?: number): boolean;
     static isSamePoint3d(dataA: Point3d, dataB: Point3d, tolerance?: number): boolean;
     static isSamePoint3dXY(dataA: Point3d, dataB: Point3d, tolerance?: number): boolean;

common/changes/@itwin/core-geometry/saeed-torabi-spiral-close-approach_2025-11-26-15-41.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/core-geometry",
+      "comment": "",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/core-geometry"
+}

core/geometry/src/Geometry.ts

@@ -353,6 +353,15 @@ export class Geometry {
       d = -d;
     return d <= tolerance;
   }
+  /**
+   * Toleranced test for equivalent fractions.
+   * @param x first fraction to compare
+   * @param y second fraction to compare
+   * @param tolerance maximum difference between fractions considered equivalent, defaulting to [[smallFraction]].
+   */
+  public static isSameFraction(x: number, y: number, tolerance: number = Geometry.smallFraction): boolean {
+    return this.isSameCoordinate(x, y, tolerance);
+  }
   /**
    * Boolean test for metric coordinate near-equality (i.e., if `x` and `y` are almost equal) using
    * `tolerance = toleranceFactor * smallMetricDistance`

core/geometry/src/curve/CurveCurve.ts

@@ -89,7 +89,7 @@ export class CurveCurve {
     for (let i = 0; i < primitives.length; i++) {
       const curveA = primitives[i];
       for (let j = i + 1; j < primitives.length; j++) {
-        handler.resetGeometry(primitives[j]);
+        handler.resetGeometryB(primitives[j]);
         curveA.dispatchToGeometryHandler(handler);
       }
     }

core/geometry/src/curve/CurveLocationDetail.ts

@@ -398,9 +398,12 @@ export class CurveLocationDetail {
     }
     return detailB;
   }
-  /** Compare only the curve and fraction of this detail with `other`. */
-  public isSameCurveAndFraction(other: CurveLocationDetail | { curve: CurvePrimitive, fraction: number }): boolean {
-    return this.curve === other.curve && Geometry.isAlmostEqualNumber(this.fraction, other.fraction);
+  /**
+   * Compare only the curve and fraction of this detail with `other`.
+   * @param fractionTol optional relative tolerance for comparing fractions with [[Geometry.isAlmostEqualNumber]].
+  */
+  public isSameCurveAndFraction(other: CurveLocationDetail | { curve: CurvePrimitive, fraction: number }, fractionTol?: number): boolean {
+    return this.curve === other.curve && Geometry.isAlmostEqualNumber(this.fraction, other.fraction, fractionTol);
   }
   /**
    * Transform the detail in place.

core/geometry/src/curve/CurvePrimitive.ts

@@ -174,8 +174,9 @@ export abstract class CurvePrimitive extends GeometryQuery {
   public abstract fractionToPointAndDerivative(fraction: number, result?: Ray3d): Ray3d;
   /**
    * Returns a ray whose origin is the curve point and direction is the unit tangent.
-   * @param fraction fractional position on the curve
+   * @param fraction fractional position on the curve.
    * @param result optional preallocated ray.
+   * @returns tangent ray with normalized direction or zero vector if the derivative vanishes.
    */
   public fractionToPointAndUnitTangent(fraction: number, result?: Ray3d): Ray3d {
     const ray = this.fractionToPointAndDerivative(fraction, result);

core/geometry/src/curve/internalContexts/ClosestPointStrokeHandler.ts

@@ -43,6 +43,8 @@ export class ClosestPointStrokeHandler extends NewtonRtoRStrokeHandler implement
     this._workPoint = Point3d.create();
     this._workRay = Ray3d.createZero();
     this._closestPoint = result;
+    if (this._closestPoint)
+      this._closestPoint.a = Geometry.largeCoordinateResult
     this._extend = extend ?? false;
     this.startCurvePrimitive(undefined);
     this._newtonSolver = new Newton1dUnboundedApproximateDerivative(this);