Replacing location_at(planar) with (x_dir)

src/build123d/topology/one_d.py

@@ -120,7 +120,11 @@ from OCP.HLRAlgo import HLRAlgo_Projector
 from OCP.HLRBRep import HLRBRep_Algo, HLRBRep_HLRToShape
 from OCP.ShapeAnalysis import ShapeAnalysis_FreeBounds
 from OCP.ShapeFix import ShapeFix_Shape, ShapeFix_Wireframe
-from OCP.Standard import Standard_Failure, Standard_NoSuchObject
+from OCP.Standard import (
+    Standard_Failure,
+    Standard_NoSuchObject,
+    Standard_ConstructionError,
+)
 from OCP.TColStd import (
     TColStd_Array1OfReal,
     TColStd_HArray1OfBoolean,
@@ -511,7 +515,8 @@ class Mixin1D(Shape):
         distance: float,
         position_mode: PositionMode = PositionMode.PARAMETER,
         frame_method: FrameMethod = FrameMethod.FRENET,
-        planar: bool = False,
+        planar: bool | None = None,
+        x_dir: VectorLike | None = None,
     ) -> Location:
         """Locations along curve
 
@@ -522,8 +527,18 @@ class Mixin1D(Shape):
             position_mode (PositionMode, optional): position calculation mode.
                 Defaults to PositionMode.PARAMETER.
             frame_method (FrameMethod, optional): moving frame calculation method.
+                The FRENET frame can “twist” or flip unexpectedly, especially near flat
+                spots. The CORRECTED frame behaves more like a “camera dolly” or
+                sweep profile would — it's smoother and more stable.
                 Defaults to FrameMethod.FRENET.
-            planar (bool, optional): planar mode. Defaults to False.
+            planar (bool, optional): planar mode. Defaults to None.
+            x_dir (VectorLike, optional): override the x_dir to help with plane
+                creation along a 1D shape. Must be perpendicalar to shapes tangent.
+                Defaults to None.
+
+        .. deprecated::
+            The `planar` parameter is deprecated and will be removed in a future release.
+            Use `x_dir` to specify orientation instead.
 
         Returns:
             Location: A Location object representing local coordinate system
@@ -550,23 +565,45 @@ class Mixin1D(Shape):
         pnt = curve.Value(param)
 
         transformation = gp_Trsf()
-        if planar:
+        if planar is not None:
+            warnings.warn(
+                "The 'planar' parameter is deprecated and will be removed in a future version. "
+                "Use 'x_dir' to control orientation instead.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+        if planar is not None and planar:
             transformation.SetTransformation(
                 gp_Ax3(pnt, gp_Dir(0, 0, 1), gp_Dir(normal.XYZ())), gp_Ax3()
             )
+        elif x_dir is not None:
+            try:
+
+                transformation.SetTransformation(
+                    gp_Ax3(pnt, gp_Dir(tangent.XYZ()), Vector(x_dir).to_dir()), gp_Ax3()
+                )
+            except Standard_ConstructionError:
+                raise ValueError(
+                    f"Unable to create location with given x_dir {x_dir}. "
+                    f"x_dir must be perpendicular to shape's tangent "
+                    f"{tuple(Vector(tangent))}."
+                )
+
         else:
             transformation.SetTransformation(
                 gp_Ax3(pnt, gp_Dir(tangent.XYZ()), gp_Dir(normal.XYZ())), gp_Ax3()
             )
+        loc = Location(TopLoc_Location(transformation))
 
-        return Location(TopLoc_Location(transformation))
+        return loc
 
     def locations(
         self,
         distances: Iterable[float],
         position_mode: PositionMode = PositionMode.PARAMETER,
         frame_method: FrameMethod = FrameMethod.FRENET,
-        planar: bool = False,
+        planar: bool | None = None,
+        x_dir: VectorLike | None = None,
     ) -> list[Location]:
         """Locations along curve
 
@@ -579,13 +616,21 @@ class Mixin1D(Shape):
             frame_method (FrameMethod, optional): moving frame calculation method.
                 Defaults to FrameMethod.FRENET.
             planar (bool, optional): planar mode. Defaults to False.
+            x_dir (VectorLike, optional): override the x_dir to help with plane
+                creation along a 1D shape. Must be perpendicalar to shapes tangent.
+                Defaults to None.
+
+        .. deprecated::
+            The `planar` parameter is deprecated and will be removed in a future release.
+            Use `x_dir` to specify orientation instead.
 
         Returns:
             list[Location]: A list of Location objects representing local coordinate
                 systems at the specified distances.
         """
         return [
-            self.location_at(d, position_mode, frame_method, planar) for d in distances
+            self.location_at(d, position_mode, frame_method, planar, x_dir)
+            for d in distances
         ]
 
     def normal(self) -> Vector:

tests/test_direct_api/test_mixin1_d.py

@@ -29,8 +29,16 @@ license:
 import math
 import unittest
 
-from build123d.build_enums import CenterOf, GeomType, PositionMode, Side, SortBy
+from build123d.build_enums import (
+    CenterOf,
+    FrameMethod,
+    GeomType,
+    PositionMode,
+    Side,
+    SortBy,
+)
 from build123d.geometry import Axis, Location, Plane, Vector
+from build123d.objects_curve import Polyline
 from build123d.objects_part import Box, Cylinder
 from build123d.topology import Compound, Edge, Face, Wire
 
@@ -201,6 +209,18 @@ class TestMixin1D(unittest.TestCase):
         self.assertAlmostEqual(loc.position, (0, 1, 0), 5)
         self.assertAlmostEqual(loc.orientation, (0, -90, -90), 5)
 
+    def test_location_at_x_dir(self):
+        path = Polyline((-50, -40), (50, -40), (50, 40), (-50, 40), close=True)
+        l1 = path.location_at(0)
+        l2 = path.location_at(0, x_dir=(0, 1, 0))
+        self.assertAlmostEqual(l1.position, l2.position, 5)
+        self.assertAlmostEqual(l1.z_axis, l2.z_axis, 5)
+        self.assertNotEqual(l1.x_axis, l2.x_axis, 5)
+        self.assertAlmostEqual(l2.x_axis, Axis(path @ 0, (0, 1, 0)), 5)
+
+        with self.assertRaises(ValueError):
+            path.location_at(0, x_dir=(1, 0, 0))
+
     def test_locations(self):
         locs = Edge.make_circle(1).locations([i / 4 for i in range(4)])
         self.assertAlmostEqual(locs[0].position, (1, 0, 0), 5)
@@ -212,6 +232,37 @@ class TestMixin1D(unittest.TestCase):
         self.assertAlmostEqual(locs[3].position, (0, -1, 0), 5)
         self.assertAlmostEqual(locs[3].orientation, (0, 90, 90), 5)
 
+    def test_location_at_corrected_frenet(self):
+        # A polyline with sharp corners — problematic for classic Frenet
+        path = Polyline((0, 0), (10, 0), (10, 10), (0, 10))
+
+        # Request multiple locations along the curve
+        locations = [
+            path.location_at(t, frame_method=FrameMethod.CORRECTED)
+            for t in [0.0, 0.25, 0.5, 0.75, 1.0]
+        ]
+        # Ensure all locations were created and have consistent orientation
+        self.assertTrue(
+            all(
+                locations[0].x_axis.direction == l.x_axis.direction
+                for l in locations[1:]
+            )
+        )
+
+        # Check that Z-axis is approximately orthogonal to X-axis
+        for loc in locations:
+            self.assertLess(abs(loc.z_axis.direction.dot(loc.x_axis.direction)), 1e-6)
+
+        # Check continuity of rotation (not flipping wildly)
+        # Check angle between x_axes doesn't flip more than ~90 degrees
+        angles = []
+        for i in range(len(locations) - 1):
+            a1 = locations[i].x_axis.direction
+            a2 = locations[i + 1].x_axis.direction
+            angle = a1.get_angle(a2)
+            angles.append(angle)
+        self.assertTrue(all(abs(angle) < 90 for angle in angles))
+
     def test_project(self):
         target = Face.make_rect(10, 10, Plane.XY.rotated((0, 45, 0)))
         circle = Edge.make_circle(1).locate(Location((0, 0, 10)))