fix: arc direction — sample midpoint from NX edge instead of cross-product
Cross product of (start-center) × (end-center) is zero for 180° arcs, causing random clockwise assignment. Now samples actual midpoint via UF Eval at t_mid, stores as 'mid' in JSON. Import prefers 'mid' over computed clockwise direction.
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@@ -109,6 +109,7 @@ class EdgeSegment:
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# Arc-specific (None for lines)
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center_3d: Point3D | None = None
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radius: float | None = None
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mid_3d: Point3D | None = None # midpoint sampled from NX edge (for arcs)
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# ---------------------------------------------------------------------------
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@@ -191,11 +192,29 @@ def _analyze_edge(edge: Any, lister: Any = None) -> EdgeSegment:
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pass
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if center is not None and radius is not None and radius > 0.0:
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# Sample midpoint on the actual NX edge for reliable arc direction
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mid_pt = None
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try:
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limits = eval_obj.AskLimits(evaluator)
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t_mid = (float(limits[0]) + float(limits[1])) / 2.0
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result = eval_obj.EvaluateUnitVectors(evaluator, t_mid)
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# Parse point from result
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if hasattr(result, '__len__') and len(result) >= 1:
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item = result[0] if hasattr(result[0], 'X') else result
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if hasattr(item, 'X'):
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mid_pt = (float(item.X), float(item.Y), float(item.Z))
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elif isinstance(item, (list, tuple)) and len(item) >= 3:
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mid_pt = (float(item[0]), float(item[1]), float(item[2]))
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if mid_pt is None and hasattr(result, 'X'):
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mid_pt = (float(result.X), float(result.Y), float(result.Z))
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except Exception as exc2:
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_log(f"[edge] Arc midpoint sampling failed: {exc2}")
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_log(f"[edge] ARC: center=({center[0]:.3f},{center[1]:.3f},{center[2]:.3f}) "
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f"r={radius:.3f}")
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f"r={radius:.3f} mid={'OK' if mid_pt else 'NONE'}")
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return EdgeSegment(
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seg_type="arc", start_3d=p1, end_3d=p2,
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center_3d=center, radius=radius,
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center_3d=center, radius=radius, mid_3d=mid_pt,
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)
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else:
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_log(f"[edge] IsArc=True but could not extract center/radius. "
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@@ -311,7 +330,7 @@ def _chain_edges_into_loops(
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found = True
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break
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elif pts_match(current_end, s.end_3d):
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# Reversed edge — swap start/end
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# Reversed edge — swap start/end (mid stays the same)
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used[i] = True
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reversed_seg = EdgeSegment(
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seg_type=s.seg_type,
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@@ -319,6 +338,7 @@ def _chain_edges_into_loops(
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end_3d=s.start_3d,
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center_3d=s.center_3d,
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radius=s.radius,
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mid_3d=s.mid_3d,
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)
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chain.append(reversed_seg)
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current_end = s.start_3d
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@@ -630,8 +650,12 @@ def _segments_to_json(segments: List[EdgeSegment], frame: LocalFrame) -> List[Di
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center_2d = _project_point_2d(seg.center_3d, frame)
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entry["center"] = [round(center_2d[0], 6), round(center_2d[1], 6)]
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entry["radius"] = round(seg.radius, 6)
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# Determine clockwise/ccw: cross product of (start-center) × (end-center)
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# projected onto the face normal
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# Store the sampled midpoint (reliable arc direction, avoids cross-product
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# degeneracy for 180° arcs)
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if seg.mid_3d is not None:
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mid_2d = _project_point_2d(seg.mid_3d, frame)
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entry["mid"] = [round(mid_2d[0], 6), round(mid_2d[1], 6)]
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# Also store clockwise as fallback (but mid is preferred)
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r1 = _sub(seg.start_3d, seg.center_3d)
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r2 = _sub(seg.end_3d, seg.center_3d)
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cross = _cross(r1, r2)
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@@ -364,28 +364,29 @@ def _draw_segment(part, seg, transform, lister):
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if seg_type == "arc" and "center" in seg:
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center_3d = unproject_point_to_3d(seg["center"], transform)
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radius = seg["radius"]
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# Compute midpoint of arc for 3-point arc creation
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cx, cy = seg["center"]
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sx, sy = seg["start"]
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ex, ey = seg["end"]
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# Angles from center
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sa = math.atan2(sy - cy, sx - cx)
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ea = math.atan2(ey - cy, ex - cx)
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clockwise = seg.get("clockwise", False)
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# Compute mid-angle
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if clockwise:
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# CW: sa → ea going clockwise (decreasing angle)
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da = sa - ea
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if da <= 0:
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da += 2 * math.pi
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mid_angle = sa - da / 2.0
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# Prefer the sampled midpoint from NX (avoids direction ambiguity)
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if "mid" in seg:
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mid_2d = seg["mid"]
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else:
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# CCW: sa → ea going counter-clockwise (increasing angle)
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da = ea - sa
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if da <= 0:
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da += 2 * math.pi
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mid_angle = sa + da / 2.0
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mid_2d = [cx + radius * math.cos(mid_angle), cy + radius * math.sin(mid_angle)]
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# Fallback: compute from clockwise flag
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cx, cy = seg["center"]
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sx, sy = seg["start"]
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ex, ey = seg["end"]
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sa = math.atan2(sy - cy, sx - cx)
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ea = math.atan2(ey - cy, ex - cx)
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clockwise = seg.get("clockwise", False)
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if clockwise:
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da = sa - ea
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if da <= 0:
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da += 2 * math.pi
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mid_angle = sa - da / 2.0
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else:
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da = ea - sa
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if da <= 0:
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da += 2 * math.pi
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mid_angle = sa + da / 2.0
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mid_2d = [cx + radius * math.cos(mid_angle), cy + radius * math.sin(mid_angle)]
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mid_3d = unproject_point_to_3d(mid_2d, transform)
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try:
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_draw_arc_3pt(part, start_3d, mid_3d, end_3d)
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