Implements business 2 geometry mapping for Viennese Bend for horizontal and cant layouts

src/ifcopenshell-python/ifcopenshell/api/alignment/_get_cant_segment.py

@@ -0,0 +1,77 @@
+# IfcOpenShell - IFC toolkit and geometry engine
+# Copyright (C) 2025 Thomas Krijnen <thomas@aecgeeks.com>
+#
+# This file is part of IfcOpenShell.
+#
+# IfcOpenShell is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# IfcOpenShell is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
+
+import ifcopenshell
+import ifcopenshell.api.alignment
+import ifcopenshell.api.geometry
+from ifcopenshell import entity_instance
+
+import math
+from collections.abc import Sequence
+
+
+def _get_cant_segment(horizontal_segment: entity_instance) -> entity_instance:
+    """
+    Returns the IfcAlignmentSegment from the cant layout that corresponds to horizontal_segment.
+    Returns None if the cant segment cannot be found
+    """
+
+    expected_type = "IfcAlignmentSegment"
+    if not horizontal_segment.is_a(expected_type):
+        raise TypeError(f"Expected {expected_type} but got {horizontal_segment.is_a()}")
+    
+    if not horizontal_segment.DesignParameters.is_a("IfcAlignmentHorizontalSegment"):
+        raise TypeError(f"Expect DesignParameter to be IfcAlignmentHorizontal but got {horizontal_segment.DesignParameters.is_a()}")
+    
+    # get the index of horizontal_segment in the horizontal_layout
+    horizontal_layout = horizontal_segment.Nests[0].RelatingObject
+    index = 0
+    for segment in horizontal_layout.IsNestedBy[0].RelatedObjects:
+        if segment == horizontal_segment:
+            break
+        else:
+            index += 1
+
+    cant_segment = None
+
+    # first check CT 4.1.4.4.1.1 Alignment Layout - Horizontal, Vertical and Cant
+    nests_layouts = horizontal_layout.Nests[0]
+    for layout in nests_layouts.RelatedObjects:
+        if layout.is_a("IfcAlignmentCant"):
+            cant_segment = layout.IsNestedBy[0].RelatedObjects[index]
+            break
+
+    # if a cant_segment wasn't found, check CT 4.1.4.4.1.2 Alignment Layout - Reusing Horizontal Layout
+    # Note that nothing forbids multiple child alignments to have cant layouts. However, this would not make
+    # sense for Viennese Bend because the Viennese Bend cant segment influences the geometry of the horizontal
+    # Viennese Bend transition curve segment. The horizontal geometry would not be unique if there are
+    # multiple child alignments with cant layouts.
+    # For this reason, use the first cant layout found
+    if cant_segment == None:
+        alignment = ifcopenshell.api.alignment.get_alignment(horizontal_layout)
+        for child_alignment in alignment.IsDecomposedBy[0].RelatedObjects:
+            for layout in child_alignment.Nests[0].RelatedObjects:
+                if layout.is_a("IfcAlignmentCant"):
+                    cant_segment = layout.IsNestedBy[0].RelatedObjects[index]
+                    break
+            if cant_segment:
+                break
+        
+
+    return cant_segment
+

src/ifcopenshell-python/ifcopenshell/api/alignment/_map_alignment_cant_segment.py

@@ -377,7 +377,66 @@ def _map_sine_curve(
 def _map_viennese_bend(
     file: ifcopenshell.file, design_parameters: entity_instance, rail_head_distance: float
 ) -> Sequence[entity_instance]:
-    raise NotImplementedError("VIENNESEBEND not implemented")
+    dist_along = design_parameters.StartDistAlong
+    length = design_parameters.HorizontalLength
+    Dsl = design_parameters.StartCantLeft
+    Del = design_parameters.EndCantLeft
+    Dsr = design_parameters.StartCantRight
+    Der = design_parameters.EndCantRight
+
+    Ds = 0.5 * (Dsl + Dsr)
+    De = 0.5 * (Del + Der)
+    f = De - Ds
+
+    a0 = Ds  # constant term
+    a1 = 0.0  # linear term
+    a2 = 0.0 * f  # quadratic term
+    a3 = 0.0 * f  # cubic term
+    a4 = 35. * f # quartic term
+    a5 = -84.*f # quintic term
+    a6 = 70.*f # sextic term
+    a7 = -20.*f # septic term
+
+    transition = "DISCONTINUOUS"
+
+    A0 = math.pow(length, 2.0 / 1.0) * math.pow(math.fabs(a0), -1.0 / 1.0) * (a0 / math.fabs(a0)) if a0 != 0.0 else 0.0
+    A1 = math.pow(length, 3.0 / 2.0) * math.pow(math.fabs(a1), -1.0 / 2.0) * (a1 / math.fabs(a1)) if a1 != 0.0 else 0.0
+    A2 = math.pow(length, 4.0 / 3.0) * math.pow(math.fabs(a2), -1.0 / 3.0) * (a2 / math.fabs(a2)) if a2 != 0.0 else 0.0
+    A3 = math.pow(length, 5.0 / 4.0) * math.pow(math.fabs(a3), -1.0 / 4.0) * (a3 / math.fabs(a3)) if a3 != 0.0 else 0.0
+    A4 = math.pow(length, 6.0 / 5.0) * math.pow(math.fabs(a4), -1.0 / 5.0) * (a4 / math.fabs(a4)) if a4 != 0.0 else 0.0
+    A5 = math.pow(length, 7.0 / 6.0) * math.pow(math.fabs(a5), -1.0 / 6.0) * (a5 / math.fabs(a5)) if a5 != 0.0 else 0.0
+    A6 = math.pow(length, 8.0 / 7.0) * math.pow(math.fabs(a6), -1.0 / 7.0) * (a6 / math.fabs(a6)) if a6 != 0.0 else 0.0
+    A7 = math.pow(length, 9.0 / 8.0) * math.pow(math.fabs(a7), -1.0 / 8.0) * (a7 / math.fabs(a7)) if a7 != 0.0 else 0.0
+
+    parent_curve = file.createIfcSeventhOrderPolynomialSpiral(
+        Position=file.createIfcAxis2Placement2D(
+            Location=file.createIfcCartesianPoint((0.0, 0.0)), RefDirection=file.createIfcDirection((1.0, 0.0))
+        ),
+        SepticTerm=A7,
+        SexticTerm=A6 if A6 != 0.0 else None,
+        QuinticTerm=A5 if A5 != 0.0 else None,
+        QuarticTerm=A4 if A4 != 0.0 else None,
+        CubicTerm=A3 if A3 != 0.0 else None,
+        QuadraticTerm=A2 if A2 != 0.0 else None,
+        LinearTerm=A1 if A1 != 0.0 else None,
+        ConstantTerm=A0 if A0 != 0.0 else None,
+    )
+
+    start_point = file.createIfcCartesianPoint((dist_along, Ds, 0.0))
+    start_direction = 0.0
+
+    curve_segment = file.createIfcCurveSegment(
+        Transition=transition,
+        Placement=file.createIfcAxis2Placement3D(
+            Location=start_point,
+            Axis=_get_axis(file, Ds, rail_head_distance),
+            RefDirection=file.createIfcDirection((math.cos(start_direction), math.sin(start_direction), 0.0)),
+        ),
+        SegmentStart=file.createIfcLengthMeasure(0.0),
+        SegmentLength=file.createIfcLengthMeasure(length),
+        ParentCurve=parent_curve,
+    )
+    return (curve_segment, None)
 
 
 def _map_alignment_cant_segment(

src/ifcopenshell-python/ifcopenshell/api/alignment/_map_alignment_horizontal_segment.py

@@ -22,6 +22,8 @@ import ifcopenshell.ifcopenshell_wrapper as ifcopenshell_wrapper
 from collections.abc import Sequence
 import math
 
+from ifcopenshell.api.alignment._get_cant_segment import _get_cant_segment
+
 
 def _get_curve_factor(design_parameters: entity_instance) -> float:
     start_radius = design_parameters.StartRadiusOfCurvature
@@ -290,22 +292,6 @@ def _map_helmert_curve(file: ifcopenshell.file, design_parameters: entity_instan
         ParentCurve=parent_curve2,
     )
 
-    """
-    import numpy as np
-    settings = ifcopenshell.geom.settings()
-    prev_segment_fn = ifcopenshell_wrapper.map_shape(settings, curve_segment1.wrapped_data)
-    prev_segment_evaluator = ifcopenshell_wrapper.function_item_evaluator(settings, prev_segment_fn)
-    e = prev_segment_evaluator.evaluate(prev_segment_fn.end())
-    end = np.array(e)
-
-    segment_fn = ifcopenshell_wrapper.map_shape(settings, curve_segment2.wrapped_data)
-    segment_evaluator = ifcopenshell_wrapper.function_item_evaluator(settings, segment_fn)
-    s = segment_evaluator.evaluate(segment_fn.start())
-    start = np.array(s)
-
-    assert(np.allclose(end[:3,3],start[:3,3]))
-    """
-
     return curve_segment1, curve_segment2
 
 
@@ -444,8 +430,87 @@ def _map_sine_curve(file: ifcopenshell.file, design_parameters: entity_instance)
     return (curve_segment, None)
 
 
-def _map_viennese_bend(file: ifcopenshell.file, design_parameters: entity_instance) -> Sequence[entity_instance]:
-    raise NotImplementedError("VIENNESEBEND not implemented")
+def _map_viennese_bend(file: ifcopenshell.file, segment: entity_instance) -> Sequence[entity_instance]:
+    design_parameters = segment.DesignParameters
+
+    start_point = design_parameters.StartPoint
+    start_direction = design_parameters.StartDirection
+    start_radius = design_parameters.StartRadiusOfCurvature
+    length = design_parameters.SegmentLength
+    gravity_centerline_height = design_parameters.GravityCenterLineHeight if design_parameters.GravityCenterLineHeight != None else 0.0
+
+    angle_unit_scale = ifcopenshell.util.unit.calculate_unit_scale(file, "PLANEANGLEUNIT")
+    start_direction *= angle_unit_scale
+
+    transition = "DISCONTINUOUS"
+
+    cant_segment = _get_cant_segment(segment)
+    if cant_segment:
+        start_cant_left = cant_segment.DesignParameters.StartCantLeft
+        end_cant_left = cant_segment.DesignParameters.EndCantLeft if cant_segment.DesignParameters.EndCantLeft else 0.0
+        start_cant_right = cant_segment.DesignParameters.StartCantRight
+        end_cant_right = cant_segment.DesignParameters.EndCantRight if cant_segment.DesignParameters.EndCantRight else 0.0
+        cant_layout = cant_segment.Nests[0].RelatingObject
+        rail_head_distance = cant_layout.RailHeadDistance
+    else:
+        start_cant_left = 0.
+        end_cant_left = 0.
+        start_cant_right = 0.
+        end_cant_right = 0.
+        rail_head_distance = 1.
+
+    cant_angle_start = (start_cant_right - start_cant_left)/rail_head_distance if rail_head_distance else 0.
+    cant_angle_end = (end_cant_right - end_cant_left)/rail_head_distance if rail_head_distance else 0.
+
+    cant_factor = -420.*(gravity_centerline_height/length)*(cant_angle_end - cant_angle_start)
+
+    f = _get_curve_factor(design_parameters)
+
+    a0 = length / start_radius if start_radius != 0.0 else 0.0 # constant term
+    a1 = 0. # linear term
+    a2 = 1.*cant_factor # quadratic term
+    a3 = -4.*cant_factor # cubic term
+    a4 = 5.*cant_factor + 35.*f # quartic term
+    a5 = -2.*cant_factor - 84.*f # quintic term
+    a6 = 70.*f # sextic term
+    a7 = -20.0*f # septic term
+
+    A0 = length*math.pow(math.fabs(a0),-1.0 / 1.0) * (a0 / math.fabs(a0)) if a0 != 0.0 else 0.0
+    A1 = length*math.pow(math.fabs(a1),-1.0 / 2.0) * (a1 / math.fabs(a1)) if a1 != 0.0 else 0.0
+    A2 = length*math.pow(math.fabs(a2),-1.0 / 3.0) * (a2 / math.fabs(a2)) if a2 != 0.0 else 0.0
+    A3 = length*math.pow(math.fabs(a3),-1.0 / 4.0) * (a3 / math.fabs(a3)) if a3 != 0.0 else 0.0
+    A4 = length*math.pow(math.fabs(a4),-1.0 / 5.0) * (a4 / math.fabs(a4)) if a4 != 0.0 else 0.0
+    A5 = length*math.pow(math.fabs(a5),-1.0 / 6.0) * (a5 / math.fabs(a5)) if a5 != 0.0 else 0.0
+    A6 = length*math.pow(math.fabs(a6),-1.0 / 7.0) * (a6 / math.fabs(a6)) if a6 != 0.0 else 0.0
+    A7 = length*math.pow(math.fabs(a7),-1.0 / 8.0) * (a7 / math.fabs(a7)) if a7 != 0.0 else 0.0
+
+    parent_curve = file.createIfcSeventhOrderPolynomialSpiral(
+        Position=file.createIfcAxis2Placement2D(
+            Location=file.createIfcCartesianPoint((0.0, 0.0)), RefDirection=file.createIfcDirection((1.0, 0.0))
+        ),
+        SepticTerm=A7,
+        SexticTerm=A6 if A6 != 0.0 else None,
+        QuinticTerm=A5 if A5 != 0.0 else None,
+        QuarticTerm=A4 if A4 != 0.0 else None,
+        CubicTerm=A3 if A3 != 0.0 else None,
+        QuadraticTerm=A2 if A2 != 0.0 else None,
+        LinearTerm=A1 if A1 != 0.0 else None,
+        ConstantTerm=A0 if A0 != 0.0 else None,
+    )
+
+    curve_segment = file.create_entity(
+        type="IfcCurveSegment",
+        Transition=transition,
+        Placement=file.create_entity(
+            type="IfcAxis2Placement2D",
+            Location=start_point,
+            RefDirection=file.createIfcDirection((math.cos(start_direction), math.sin(start_direction))),
+        ),
+        SegmentStart=file.createIfcLengthMeasure(0.0),
+        SegmentLength=file.createIfcLengthMeasure(length),
+        ParentCurve=parent_curve,
+    )
+    return (curve_segment, None)
 
 
 def _map_alignment_horizontal_segment(file: ifcopenshell.file, segment: entity_instance) -> Sequence[entity_instance]:
@@ -477,7 +542,7 @@ def _map_alignment_horizontal_segment(file: ifcopenshell.file, segment: entity_i
     elif predefined_type == "SINECURVE":
         result = _map_sine_curve(file, segment.DesignParameters)
     elif predefined_type == "VIENNESEBEND":
-        result = _map_viennese_bend(file, segment.DesignParameters)
+        result = _map_viennese_bend(file, segment)
     else:
         raise TypeError(f"Unexpected predefined type: '{predefined_type}'.")
 

src/ifcopenshell-python/ifcopenshell/api/alignment/create.py

@@ -46,6 +46,9 @@ def create(
 
     Use get_horizontal_layout(alignment) to get the IfcAlignmentHorizontal layout.
 
+    If the alignment has Viennese Bend transition curves, create the cant layout before the horizontal layout. This is because the horizontal layout
+    in the Viennese Bend transition curves depends on the Viennese Bend cant parameters.
+
     :param file:
     :param name: name assigned to IfcAlignment.Name
     :param include_vertical: If True, IfcAlignmentVertical and IfcGradientCurve are created